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Introduction to Applied Colloidand Surface Chemistry

Introduction to Applied Colloidand Surface Chemistry

GEORGIOS M KONTOGEORGIS AND SOslashREN KIILDepartment of Chemical and Biochemical Engineering

Technical University of DenmarkDenmark

This edition first published 2016copy 2016 John Wiley amp Sons Ltd

Registered OfficeJohn Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ United Kingdom

For details of our global editorial offices for customer services and for information about how to apply for permission to reuse the copyright material inthis book please see our website at wwwwileycom

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright Designs and Patents Act 1988

All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronicmechanical photocopying recording or otherwise except as permitted by the UK Copyright Designs and Patents Act 1988 without the prior permissionof the publisher

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books

Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book aretrade names service marks trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendormentioned in this book

Limit of LiabilityDisclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representationsor warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantabilityor fitness for a particular purpose It is sold on the understanding that the publisher is not engaged in rendering professional services and neither thepublisher nor the author shall be liable for damages arising herefrom If professional advice or other expert assistance is required the services of a competentprofessional should be sought

The advice and strategies contained herein may not be suitable for every situation In view of ongoing research equipment modifications changes ingovernmental regulations and the constant flow of information relating to the use of experimental reagents equipment and devices the reader is urged to reviewand evaluate the information provided in the package insert or instructions for each chemical piece of equipment reagent or device for among other thingsany changes in the instructions or indication of usage and for added warnings and precautions The fact that an organization or Website is referred to inthis work as a citation andor a potential source of further information does not mean that the author or the publisher endorses the information the organization orWebsite may provide or recommendations it may make Further readers should be aware that Internet Websites listed in this work may have changed ordisappeared between when this work was written and when it is read No warranty may be created or extended by any promotional statements for this workNeither the publisher nor the author shall be liable for any damages arising herefrom

Library of Congress Cataloging-in-Publication Data

Names Kontogeorgis Georgios M author | Kiil Soslashren authorTitle Introduction to applied colloid and surface chemistry Georgios M

Kontogeorgis and Soslashren KiilDescription Chichester UK Hoboken NJ John Wiley amp Sons 2016 |

Includes bibliographical references and indexIdentifiers LCCN 2015045696 | ISBN 9781118881187 (pbk) | ISBN 9781118881217 (ePDF) | ISBN 9781118881200 (ePUB)Subjects LCSH Surface chemistry | ColloidsClassification LCC QD506 K645 2016 | DDC 54133ndashdc23LC record available at httplccnlocgov2015045696

A catalogue record for this book is available from the British Library

Cover image Rudisill PLAINVIEW Wragg MargouillatphotosGetty

Set in 1012pt Times by SPi Global Pondicherry India

1 2016

Introduction to Applied Colloidand Surface Chemistry

Introduction to Applied Colloidand Surface Chemistry

GEORGIOS M KONTOGEORGIS AND SOslashREN KIILDepartment of Chemical and Biochemical Engineering

Technical University of DenmarkDenmark

This edition first published 2016copy 2016 John Wiley amp Sons Ltd

Registered OfficeJohn Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ United Kingdom

For details of our global editorial offices for customer services and for information about how to apply for permission to reuse the copyright material inthis book please see our website at wwwwileycom

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright Designs and Patents Act 1988

All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronicmechanical photocopying recording or otherwise except as permitted by the UK Copyright Designs and Patents Act 1988 without the prior permissionof the publisher

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books

Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book aretrade names service marks trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendormentioned in this book

Limit of LiabilityDisclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representationsor warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantabilityor fitness for a particular purpose It is sold on the understanding that the publisher is not engaged in rendering professional services and neither thepublisher nor the author shall be liable for damages arising herefrom If professional advice or other expert assistance is required the services of a competentprofessional should be sought

The advice and strategies contained herein may not be suitable for every situation In view of ongoing research equipment modifications changes ingovernmental regulations and the constant flow of information relating to the use of experimental reagents equipment and devices the reader is urged to reviewand evaluate the information provided in the package insert or instructions for each chemical piece of equipment reagent or device for among other thingsany changes in the instructions or indication of usage and for added warnings and precautions The fact that an organization or Website is referred to inthis work as a citation andor a potential source of further information does not mean that the author or the publisher endorses the information the organization orWebsite may provide or recommendations it may make Further readers should be aware that Internet Websites listed in this work may have changed ordisappeared between when this work was written and when it is read No warranty may be created or extended by any promotional statements for this workNeither the publisher nor the author shall be liable for any damages arising herefrom

Library of Congress Cataloging-in-Publication Data

Names Kontogeorgis Georgios M author | Kiil Soslashren authorTitle Introduction to applied colloid and surface chemistry Georgios M

Kontogeorgis and Soslashren KiilDescription Chichester UK Hoboken NJ John Wiley amp Sons 2016 |

Includes bibliographical references and indexIdentifiers LCCN 2015045696 | ISBN 9781118881187 (pbk) | ISBN 9781118881217 (ePDF) | ISBN 9781118881200 (ePUB)Subjects LCSH Surface chemistry | ColloidsClassification LCC QD506 K645 2016 | DDC 54133ndashdc23LC record available at httplccnlocgov2015045696

A catalogue record for this book is available from the British Library

Cover image Rudisill PLAINVIEW Wragg MargouillatphotosGetty

Set in 1012pt Times by SPi Global Pondicherry India

1 2016

Introduction to Applied Colloidand Surface Chemistry

GEORGIOS M KONTOGEORGIS AND SOslashREN KIILDepartment of Chemical and Biochemical Engineering

Technical University of DenmarkDenmark

This edition first published 2016copy 2016 John Wiley amp Sons Ltd

Registered OfficeJohn Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ United Kingdom

For details of our global editorial offices for customer services and for information about how to apply for permission to reuse the copyright material inthis book please see our website at wwwwileycom

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright Designs and Patents Act 1988

All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronicmechanical photocopying recording or otherwise except as permitted by the UK Copyright Designs and Patents Act 1988 without the prior permissionof the publisher

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books

Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book aretrade names service marks trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendormentioned in this book

Limit of LiabilityDisclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representationsor warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantabilityor fitness for a particular purpose It is sold on the understanding that the publisher is not engaged in rendering professional services and neither thepublisher nor the author shall be liable for damages arising herefrom If professional advice or other expert assistance is required the services of a competentprofessional should be sought

The advice and strategies contained herein may not be suitable for every situation In view of ongoing research equipment modifications changes ingovernmental regulations and the constant flow of information relating to the use of experimental reagents equipment and devices the reader is urged to reviewand evaluate the information provided in the package insert or instructions for each chemical piece of equipment reagent or device for among other thingsany changes in the instructions or indication of usage and for added warnings and precautions The fact that an organization or Website is referred to inthis work as a citation andor a potential source of further information does not mean that the author or the publisher endorses the information the organization orWebsite may provide or recommendations it may make Further readers should be aware that Internet Websites listed in this work may have changed ordisappeared between when this work was written and when it is read No warranty may be created or extended by any promotional statements for this workNeither the publisher nor the author shall be liable for any damages arising herefrom

Library of Congress Cataloging-in-Publication Data

Names Kontogeorgis Georgios M author | Kiil Soslashren authorTitle Introduction to applied colloid and surface chemistry Georgios M

Kontogeorgis and Soslashren KiilDescription Chichester UK Hoboken NJ John Wiley amp Sons 2016 |

Includes bibliographical references and indexIdentifiers LCCN 2015045696 | ISBN 9781118881187 (pbk) | ISBN 9781118881217 (ePDF) | ISBN 9781118881200 (ePUB)Subjects LCSH Surface chemistry | ColloidsClassification LCC QD506 K645 2016 | DDC 54133ndashdc23LC record available at httplccnlocgov2015045696

A catalogue record for this book is available from the British Library

Cover image Rudisill PLAINVIEW Wragg MargouillatphotosGetty

Set in 1012pt Times by SPi Global Pondicherry India

1 2016

This edition first published 2016copy 2016 John Wiley amp Sons Ltd

Registered OfficeJohn Wiley amp Sons Ltd The Atrium Southern Gate Chichester West Sussex PO19 8SQ United Kingdom

For details of our global editorial offices for customer services and for information about how to apply for permission to reuse the copyright material inthis book please see our website at wwwwileycom

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright Designs and Patents Act 1988

All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronicmechanical photocopying recording or otherwise except as permitted by the UK Copyright Designs and Patents Act 1988 without the prior permissionof the publisher

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books

Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book aretrade names service marks trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendormentioned in this book

Limit of LiabilityDisclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representationsor warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantabilityor fitness for a particular purpose It is sold on the understanding that the publisher is not engaged in rendering professional services and neither thepublisher nor the author shall be liable for damages arising herefrom If professional advice or other expert assistance is required the services of a competentprofessional should be sought

The advice and strategies contained herein may not be suitable for every situation In view of ongoing research equipment modifications changes ingovernmental regulations and the constant flow of information relating to the use of experimental reagents equipment and devices the reader is urged to reviewand evaluate the information provided in the package insert or instructions for each chemical piece of equipment reagent or device for among other thingsany changes in the instructions or indication of usage and for added warnings and precautions The fact that an organization or Website is referred to inthis work as a citation andor a potential source of further information does not mean that the author or the publisher endorses the information the organization orWebsite may provide or recommendations it may make Further readers should be aware that Internet Websites listed in this work may have changed ordisappeared between when this work was written and when it is read No warranty may be created or extended by any promotional statements for this workNeither the publisher nor the author shall be liable for any damages arising herefrom

Library of Congress Cataloging-in-Publication Data

Names Kontogeorgis Georgios M author | Kiil Soslashren authorTitle Introduction to applied colloid and surface chemistry Georgios M

Kontogeorgis and Soslashren KiilDescription Chichester UK Hoboken NJ John Wiley amp Sons 2016 |

Includes bibliographical references and indexIdentifiers LCCN 2015045696 | ISBN 9781118881187 (pbk) | ISBN 9781118881217 (ePDF) | ISBN 9781118881200 (ePUB)Subjects LCSH Surface chemistry | ColloidsClassification LCC QD506 K645 2016 | DDC 54133ndashdc23LC record available at httplccnlocgov2015045696

A catalogue record for this book is available from the British Library

Cover image Rudisill PLAINVIEW Wragg MargouillatphotosGetty

Set in 1012pt Times by SPi Global Pondicherry India

1 2016

Contents

Preface xiUseful Constants xviSymbols and Some Basic Abbreviations xviiAbout the Companion Web Site xx

1 Introduction to Colloid and Surface Chemistry 111 What are the colloids and interfaces Why are they important Why do we study

them together 1111 Colloids and interfaces 3

12 Applications 413 Three ways of classifying the colloids 514 How to prepare colloid systems 615 Key properties of colloids 716 Concluding remarks 7Appendix 11 8Problems 9References 10

2 Intermolecular and Interparticle Forces 1121 Introduction ndash Why and which forces are of importance in colloid and surface chemistry 1122 Two important long-range forces between molecules 1223 The van der Waals forces 15

231 Van der Waals forces between molecules 15232 Forces between particles and surfaces 16233 Importance of the van der Waals forces 21

24 Concluding remarks 25Appendix 21 A note on the uniqueness of the water molecule and some of the recent debateson water structure and peculiar properties 26References for the Appendix 21 28Problems 29References 33

3 Surface and Interfacial Tensions ndash Principles and Estimation Methods 3431 Introduction 3432 Concept of surface tension ndash applications 3433 Interfacial tensions work of adhesion and spreading 39

331 Interfacial tensions 39332 Work of adhesion and cohesion 43333 Spreading coefficient in liquidndashliquid interfaces 44

34 Measurement and estimation methods for surface tensions 45341 The parachor method 46342 Other methods 48

35 Measurement and estimation methods for interfacial tensions 50351 ldquoDirectrdquo theories (GirifalcondashGood and Neumann) 51352 Early ldquosurface componentrdquo theories (Fowkes OwensndashWendt HansenSkaarup) 52353 Acidndashbase theory of van OssndashGood (van Oss et al 1987) ndash possibly the best

theory to-date 57354 Discussion 59

36 Summary 60Appendix 31 Hansen solubility parameters (HSP) for selected solvents 61Appendix 32 The ldquoφrdquo parameter of the GirifalcondashGood equation (Equation 316) forliquidndashliquid interfaces Data from Girifalco and Good (1957 1960) 66Problems 67References 72

4 Fundamental Equations in Colloid and Surface Science 7441 Introduction 7442 The Young equation of contact angle 74

421 Contact angle spreading pressure and work of adhesion for solidndashliquid interfaces 74422 Validity of the Young equation 77423 Complexity of solid surfaces and effects on contact angle 78

43 YoungndashLaplace equation for the pressure difference across a curved surface 7944 Kelvin equation for the vapour pressure P of a droplet (curved surface) over the ldquoordinaryrdquo

vapour pressure Psat for a flat surface 80441 Applications of the Kelvin equation 81

45 The Gibbs adsorption equation 8246 Applications of the Gibbs equation (adsorption monolayers molecular weight of proteins) 8347 Monolayers 8648 Conclusions 89Appendix 41 Derivation of the YoungndashLaplace equation 90Appendix 42 Derivation of the Kelvin equation 91Appendix 43 Derivation of the Gibbs adsorption equation 91Problems 93References 95

5 Surfactants and Self-assembly Detergents and Cleaning 9651 Introduction to surfactants ndash basic properties self-assembly and critical packing

parameter (CPP) 9652 Micelles and critical micelle concentration (CMC) 99

vi Contents

53 Micellization ndash theories and key parameters 10654 Surfactants and cleaning (detergency) 11255 Other applications of surfactants 11356 Concluding remarks 114Appendix 51 Useful relationships from geometry 115Appendix 52 The HydrophilicndashLipophilic Balance (HLB) 116Problems 117References 119

6 Wetting and Adhesion 12161 Introduction 12162 Wetting and adhesion via the Zisman plot and theories for interfacial tensions 122

621 Zisman plot 122622 Combining theories of interfacial tensions with Young equation and work of

adhesion for studying wetting and adhesion 124623 Applications of wetting and solid characterization 130

63 Adhesion theories 141631 Introduction ndash adhesion theories 141632 Adhesive forces 144

64 Practical adhesion forces work of adhesion problems and protection 147641 Effect of surface phenomena and mechanical properties 147642 Practical adhesion ndash locus of failure 148643 Adhesion problems and some solutions 149

65 Concluding remarks 154Problems 155References 160

7 Adsorption in Colloid and Surface Science ndash A Universal Concept 16171 Introduction ndash universality of adsorption ndash overview 16172 Adsorption theories two-dimensional equations of state and surface tensionndashconcentration

trends a clear relationship 16173 Adsorption of gases on solids 162

731 Adsorption using the Langmuir equation 163732 Adsorption of gases on solids using the BET equation 164

74 Adsorption from solution 168741 Adsorption using the Langmuir equation 168742 Adsorption from solution ndash the effect of solvent and concentration on adsorption 171

75 Adsorption of surfactants and polymers 173751 Adsorption of surfactants and the role of CPP 173752 Adsorption of polymers 174

76 Concluding remarks 179Problems 180References 184

8 Characterization Methods of Colloids ndash Part I Kinetic Properties and Rheology 18581 Introduction ndash importance of kinetic properties 18582 Brownian motion 185

Contents vii

83 Sedimentation and creaming (Stokes and Einstein equations) 187831 Stokes equation 187832 Effect of particle shape 188833 Einstein equation 190

84 Kinetic properties via the ultracentrifuge 191841 Molecular weight estimated from kinetic experiments (1 = medium and

2 = particle or droplet) 193842 Sedimentation velocity experiments (1 = medium and 2 = particle or droplet) 193

85 Osmosis and osmotic pressure 19386 Rheology of colloidal dispersions 194

861 Introduction 194862 Special characteristics of colloid dispersionsrsquo rheology 196

87 Concluding remarks 198Problems 198References 201

9 Characterization Methods of Colloids ndash Part II Optical Properties (ScatteringSpectroscopy and Microscopy) 20291 Introduction 20292 Optical microscopy 20293 Electron microscopy 20494 Atomic force microscopy 20695 Light scattering 20796 Spectroscopy 20997 Concluding remarks 210Problems 210References 210

10 Colloid Stability ndash Part I The Major Players (van der Waals and Electrical Forces) 211101 Introduction ndash key forces and potential energy plots ndash overview 211

1011 Critical coagulation concentration 213102 van der Waals forces between particles and surfaces ndash basics 214103 Estimation of effective Hamaker constants 215104 vdW forces for different geometries ndash some examples 217

1041 Complex fluids 219105 Electrostatic forces the electric double layer and the origin of surface charge 219106 Electrical forces key parameters (Debye length and zeta potential) 222

1061 Surface or zeta potential and electrophoretic experiments 2231062 The Debye length 225

107 Electrical forces 2281071 Effect of particle concentration in a dispersion 229

108 SchulzendashHardy rule and the critical coagulation concentration (CCC) 230109 Concluding remarks on colloid stability the vdW and electric forces 233

1091 vdW forces 2331092 Electric forces 234

Appendix 101 A note on the terminology of colloid stability 235

viii Contents

Appendix 102 GouyndashChapman theory of the diffuse electrical double-layer 236Problems 238References 242

11 Colloid Stability ndash Part II The DLVO Theory ndash Kinetics of Aggregation 243111 DLVO theory ndash a rapid overview 243112 DLVO theory ndash effect of various parameters 244113 DLVO theory ndash experimental verification and applications 245

1131 Critical coagulation concentration and the Hofmeister series 2451132 DLVO experiments and limitations 247

114 Kinetics of aggregation 2551141 General ndash the Smoluchowski model 2551142 Fast (diffusion-controlled) coagulation 2551143 Stability ratio W 2551144 Structure of aggregates 257

115 Concluding remarks 264Problems 265References 268

12 Emulsions 269121 Introduction 269122 Applications and characterization of emulsions 269123 Destabilization of emulsions 272124 Emulsion stability 273125 Quantitative representation of the steric stabilization 275

1251 Temperature-dependency of steric stabilization 2761252 Conditions for good stabilization 277

126 Emulsion design 278127 PIT ndash Phase inversion temperature of emulsion based on non-ionic emulsifiers 279128 Concluding remarks 279Problems 280References 282

13 Foams 283131 Introduction 283132 Applications of foams 283133 Characterization of foams 285134 Preparation of foams 287135 Measurements of foam stability 287136 Destabilization of foams 288

1361 Gas diffusion 2891362 Film (lamella) rupture 2901363 Drainage of foam by gravity 291

137 Stabilization of foams 2931371 Changing surface viscosity 2931372 Surface elasticity 293

Contents ix

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

3 Surface and Interfacial Tensions ndash Principles and Estimation Methods 3431 Introduction 3432 Concept of surface tension ndash applications 3433 Interfacial tensions work of adhesion and spreading 39

331 Interfacial tensions 39332 Work of adhesion and cohesion 43333 Spreading coefficient in liquidndashliquid interfaces 44

34 Measurement and estimation methods for surface tensions 45341 The parachor method 46342 Other methods 48

35 Measurement and estimation methods for interfacial tensions 50351 ldquoDirectrdquo theories (GirifalcondashGood and Neumann) 51352 Early ldquosurface componentrdquo theories (Fowkes OwensndashWendt HansenSkaarup) 52353 Acidndashbase theory of van OssndashGood (van Oss et al 1987) ndash possibly the best

theory to-date 57354 Discussion 59

36 Summary 60Appendix 31 Hansen solubility parameters (HSP) for selected solvents 61Appendix 32 The ldquoφrdquo parameter of the GirifalcondashGood equation (Equation 316) forliquidndashliquid interfaces Data from Girifalco and Good (1957 1960) 66Problems 67References 72

4 Fundamental Equations in Colloid and Surface Science 7441 Introduction 7442 The Young equation of contact angle 74

421 Contact angle spreading pressure and work of adhesion for solidndashliquid interfaces 74422 Validity of the Young equation 77423 Complexity of solid surfaces and effects on contact angle 78

43 YoungndashLaplace equation for the pressure difference across a curved surface 7944 Kelvin equation for the vapour pressure P of a droplet (curved surface) over the ldquoordinaryrdquo

vapour pressure Psat for a flat surface 80441 Applications of the Kelvin equation 81

45 The Gibbs adsorption equation 8246 Applications of the Gibbs equation (adsorption monolayers molecular weight of proteins) 8347 Monolayers 8648 Conclusions 89Appendix 41 Derivation of the YoungndashLaplace equation 90Appendix 42 Derivation of the Kelvin equation 91Appendix 43 Derivation of the Gibbs adsorption equation 91Problems 93References 95

5 Surfactants and Self-assembly Detergents and Cleaning 9651 Introduction to surfactants ndash basic properties self-assembly and critical packing

parameter (CPP) 9652 Micelles and critical micelle concentration (CMC) 99

vi Contents

53 Micellization ndash theories and key parameters 10654 Surfactants and cleaning (detergency) 11255 Other applications of surfactants 11356 Concluding remarks 114Appendix 51 Useful relationships from geometry 115Appendix 52 The HydrophilicndashLipophilic Balance (HLB) 116Problems 117References 119

6 Wetting and Adhesion 12161 Introduction 12162 Wetting and adhesion via the Zisman plot and theories for interfacial tensions 122

621 Zisman plot 122622 Combining theories of interfacial tensions with Young equation and work of

adhesion for studying wetting and adhesion 124623 Applications of wetting and solid characterization 130

63 Adhesion theories 141631 Introduction ndash adhesion theories 141632 Adhesive forces 144

64 Practical adhesion forces work of adhesion problems and protection 147641 Effect of surface phenomena and mechanical properties 147642 Practical adhesion ndash locus of failure 148643 Adhesion problems and some solutions 149

65 Concluding remarks 154Problems 155References 160

7 Adsorption in Colloid and Surface Science ndash A Universal Concept 16171 Introduction ndash universality of adsorption ndash overview 16172 Adsorption theories two-dimensional equations of state and surface tensionndashconcentration

trends a clear relationship 16173 Adsorption of gases on solids 162

731 Adsorption using the Langmuir equation 163732 Adsorption of gases on solids using the BET equation 164

74 Adsorption from solution 168741 Adsorption using the Langmuir equation 168742 Adsorption from solution ndash the effect of solvent and concentration on adsorption 171

75 Adsorption of surfactants and polymers 173751 Adsorption of surfactants and the role of CPP 173752 Adsorption of polymers 174

76 Concluding remarks 179Problems 180References 184

8 Characterization Methods of Colloids ndash Part I Kinetic Properties and Rheology 18581 Introduction ndash importance of kinetic properties 18582 Brownian motion 185

Contents vii

83 Sedimentation and creaming (Stokes and Einstein equations) 187831 Stokes equation 187832 Effect of particle shape 188833 Einstein equation 190

84 Kinetic properties via the ultracentrifuge 191841 Molecular weight estimated from kinetic experiments (1 = medium and

2 = particle or droplet) 193842 Sedimentation velocity experiments (1 = medium and 2 = particle or droplet) 193

85 Osmosis and osmotic pressure 19386 Rheology of colloidal dispersions 194

861 Introduction 194862 Special characteristics of colloid dispersionsrsquo rheology 196

87 Concluding remarks 198Problems 198References 201

9 Characterization Methods of Colloids ndash Part II Optical Properties (ScatteringSpectroscopy and Microscopy) 20291 Introduction 20292 Optical microscopy 20293 Electron microscopy 20494 Atomic force microscopy 20695 Light scattering 20796 Spectroscopy 20997 Concluding remarks 210Problems 210References 210

10 Colloid Stability ndash Part I The Major Players (van der Waals and Electrical Forces) 211101 Introduction ndash key forces and potential energy plots ndash overview 211

1011 Critical coagulation concentration 213102 van der Waals forces between particles and surfaces ndash basics 214103 Estimation of effective Hamaker constants 215104 vdW forces for different geometries ndash some examples 217

1041 Complex fluids 219105 Electrostatic forces the electric double layer and the origin of surface charge 219106 Electrical forces key parameters (Debye length and zeta potential) 222

1061 Surface or zeta potential and electrophoretic experiments 2231062 The Debye length 225

107 Electrical forces 2281071 Effect of particle concentration in a dispersion 229

108 SchulzendashHardy rule and the critical coagulation concentration (CCC) 230109 Concluding remarks on colloid stability the vdW and electric forces 233

1091 vdW forces 2331092 Electric forces 234

Appendix 101 A note on the terminology of colloid stability 235

viii Contents

Appendix 102 GouyndashChapman theory of the diffuse electrical double-layer 236Problems 238References 242

11 Colloid Stability ndash Part II The DLVO Theory ndash Kinetics of Aggregation 243111 DLVO theory ndash a rapid overview 243112 DLVO theory ndash effect of various parameters 244113 DLVO theory ndash experimental verification and applications 245

1131 Critical coagulation concentration and the Hofmeister series 2451132 DLVO experiments and limitations 247

114 Kinetics of aggregation 2551141 General ndash the Smoluchowski model 2551142 Fast (diffusion-controlled) coagulation 2551143 Stability ratio W 2551144 Structure of aggregates 257

115 Concluding remarks 264Problems 265References 268

12 Emulsions 269121 Introduction 269122 Applications and characterization of emulsions 269123 Destabilization of emulsions 272124 Emulsion stability 273125 Quantitative representation of the steric stabilization 275

1251 Temperature-dependency of steric stabilization 2761252 Conditions for good stabilization 277

126 Emulsion design 278127 PIT ndash Phase inversion temperature of emulsion based on non-ionic emulsifiers 279128 Concluding remarks 279Problems 280References 282

13 Foams 283131 Introduction 283132 Applications of foams 283133 Characterization of foams 285134 Preparation of foams 287135 Measurements of foam stability 287136 Destabilization of foams 288

1361 Gas diffusion 2891362 Film (lamella) rupture 2901363 Drainage of foam by gravity 291

137 Stabilization of foams 2931371 Changing surface viscosity 2931372 Surface elasticity 293

Contents ix

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

53 Micellization ndash theories and key parameters 10654 Surfactants and cleaning (detergency) 11255 Other applications of surfactants 11356 Concluding remarks 114Appendix 51 Useful relationships from geometry 115Appendix 52 The HydrophilicndashLipophilic Balance (HLB) 116Problems 117References 119

6 Wetting and Adhesion 12161 Introduction 12162 Wetting and adhesion via the Zisman plot and theories for interfacial tensions 122

621 Zisman plot 122622 Combining theories of interfacial tensions with Young equation and work of

adhesion for studying wetting and adhesion 124623 Applications of wetting and solid characterization 130

63 Adhesion theories 141631 Introduction ndash adhesion theories 141632 Adhesive forces 144

64 Practical adhesion forces work of adhesion problems and protection 147641 Effect of surface phenomena and mechanical properties 147642 Practical adhesion ndash locus of failure 148643 Adhesion problems and some solutions 149

65 Concluding remarks 154Problems 155References 160

7 Adsorption in Colloid and Surface Science ndash A Universal Concept 16171 Introduction ndash universality of adsorption ndash overview 16172 Adsorption theories two-dimensional equations of state and surface tensionndashconcentration

trends a clear relationship 16173 Adsorption of gases on solids 162

731 Adsorption using the Langmuir equation 163732 Adsorption of gases on solids using the BET equation 164

74 Adsorption from solution 168741 Adsorption using the Langmuir equation 168742 Adsorption from solution ndash the effect of solvent and concentration on adsorption 171

75 Adsorption of surfactants and polymers 173751 Adsorption of surfactants and the role of CPP 173752 Adsorption of polymers 174

76 Concluding remarks 179Problems 180References 184

8 Characterization Methods of Colloids ndash Part I Kinetic Properties and Rheology 18581 Introduction ndash importance of kinetic properties 18582 Brownian motion 185

Contents vii

83 Sedimentation and creaming (Stokes and Einstein equations) 187831 Stokes equation 187832 Effect of particle shape 188833 Einstein equation 190

84 Kinetic properties via the ultracentrifuge 191841 Molecular weight estimated from kinetic experiments (1 = medium and

2 = particle or droplet) 193842 Sedimentation velocity experiments (1 = medium and 2 = particle or droplet) 193

85 Osmosis and osmotic pressure 19386 Rheology of colloidal dispersions 194

861 Introduction 194862 Special characteristics of colloid dispersionsrsquo rheology 196

87 Concluding remarks 198Problems 198References 201

9 Characterization Methods of Colloids ndash Part II Optical Properties (ScatteringSpectroscopy and Microscopy) 20291 Introduction 20292 Optical microscopy 20293 Electron microscopy 20494 Atomic force microscopy 20695 Light scattering 20796 Spectroscopy 20997 Concluding remarks 210Problems 210References 210

10 Colloid Stability ndash Part I The Major Players (van der Waals and Electrical Forces) 211101 Introduction ndash key forces and potential energy plots ndash overview 211

1011 Critical coagulation concentration 213102 van der Waals forces between particles and surfaces ndash basics 214103 Estimation of effective Hamaker constants 215104 vdW forces for different geometries ndash some examples 217

1041 Complex fluids 219105 Electrostatic forces the electric double layer and the origin of surface charge 219106 Electrical forces key parameters (Debye length and zeta potential) 222

1061 Surface or zeta potential and electrophoretic experiments 2231062 The Debye length 225

107 Electrical forces 2281071 Effect of particle concentration in a dispersion 229

108 SchulzendashHardy rule and the critical coagulation concentration (CCC) 230109 Concluding remarks on colloid stability the vdW and electric forces 233

1091 vdW forces 2331092 Electric forces 234

Appendix 101 A note on the terminology of colloid stability 235

viii Contents

Appendix 102 GouyndashChapman theory of the diffuse electrical double-layer 236Problems 238References 242

11 Colloid Stability ndash Part II The DLVO Theory ndash Kinetics of Aggregation 243111 DLVO theory ndash a rapid overview 243112 DLVO theory ndash effect of various parameters 244113 DLVO theory ndash experimental verification and applications 245

1131 Critical coagulation concentration and the Hofmeister series 2451132 DLVO experiments and limitations 247

114 Kinetics of aggregation 2551141 General ndash the Smoluchowski model 2551142 Fast (diffusion-controlled) coagulation 2551143 Stability ratio W 2551144 Structure of aggregates 257

115 Concluding remarks 264Problems 265References 268

12 Emulsions 269121 Introduction 269122 Applications and characterization of emulsions 269123 Destabilization of emulsions 272124 Emulsion stability 273125 Quantitative representation of the steric stabilization 275

1251 Temperature-dependency of steric stabilization 2761252 Conditions for good stabilization 277

126 Emulsion design 278127 PIT ndash Phase inversion temperature of emulsion based on non-ionic emulsifiers 279128 Concluding remarks 279Problems 280References 282

13 Foams 283131 Introduction 283132 Applications of foams 283133 Characterization of foams 285134 Preparation of foams 287135 Measurements of foam stability 287136 Destabilization of foams 288

1361 Gas diffusion 2891362 Film (lamella) rupture 2901363 Drainage of foam by gravity 291

137 Stabilization of foams 2931371 Changing surface viscosity 2931372 Surface elasticity 293

Contents ix

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

83 Sedimentation and creaming (Stokes and Einstein equations) 187831 Stokes equation 187832 Effect of particle shape 188833 Einstein equation 190

84 Kinetic properties via the ultracentrifuge 191841 Molecular weight estimated from kinetic experiments (1 = medium and

2 = particle or droplet) 193842 Sedimentation velocity experiments (1 = medium and 2 = particle or droplet) 193

85 Osmosis and osmotic pressure 19386 Rheology of colloidal dispersions 194

861 Introduction 194862 Special characteristics of colloid dispersionsrsquo rheology 196

87 Concluding remarks 198Problems 198References 201

9 Characterization Methods of Colloids ndash Part II Optical Properties (ScatteringSpectroscopy and Microscopy) 20291 Introduction 20292 Optical microscopy 20293 Electron microscopy 20494 Atomic force microscopy 20695 Light scattering 20796 Spectroscopy 20997 Concluding remarks 210Problems 210References 210

10 Colloid Stability ndash Part I The Major Players (van der Waals and Electrical Forces) 211101 Introduction ndash key forces and potential energy plots ndash overview 211

1011 Critical coagulation concentration 213102 van der Waals forces between particles and surfaces ndash basics 214103 Estimation of effective Hamaker constants 215104 vdW forces for different geometries ndash some examples 217

1041 Complex fluids 219105 Electrostatic forces the electric double layer and the origin of surface charge 219106 Electrical forces key parameters (Debye length and zeta potential) 222

1061 Surface or zeta potential and electrophoretic experiments 2231062 The Debye length 225

107 Electrical forces 2281071 Effect of particle concentration in a dispersion 229

108 SchulzendashHardy rule and the critical coagulation concentration (CCC) 230109 Concluding remarks on colloid stability the vdW and electric forces 233

1091 vdW forces 2331092 Electric forces 234

Appendix 101 A note on the terminology of colloid stability 235

viii Contents

Appendix 102 GouyndashChapman theory of the diffuse electrical double-layer 236Problems 238References 242

11 Colloid Stability ndash Part II The DLVO Theory ndash Kinetics of Aggregation 243111 DLVO theory ndash a rapid overview 243112 DLVO theory ndash effect of various parameters 244113 DLVO theory ndash experimental verification and applications 245

1131 Critical coagulation concentration and the Hofmeister series 2451132 DLVO experiments and limitations 247

114 Kinetics of aggregation 2551141 General ndash the Smoluchowski model 2551142 Fast (diffusion-controlled) coagulation 2551143 Stability ratio W 2551144 Structure of aggregates 257

115 Concluding remarks 264Problems 265References 268

12 Emulsions 269121 Introduction 269122 Applications and characterization of emulsions 269123 Destabilization of emulsions 272124 Emulsion stability 273125 Quantitative representation of the steric stabilization 275

1251 Temperature-dependency of steric stabilization 2761252 Conditions for good stabilization 277

126 Emulsion design 278127 PIT ndash Phase inversion temperature of emulsion based on non-ionic emulsifiers 279128 Concluding remarks 279Problems 280References 282

13 Foams 283131 Introduction 283132 Applications of foams 283133 Characterization of foams 285134 Preparation of foams 287135 Measurements of foam stability 287136 Destabilization of foams 288

1361 Gas diffusion 2891362 Film (lamella) rupture 2901363 Drainage of foam by gravity 291

137 Stabilization of foams 2931371 Changing surface viscosity 2931372 Surface elasticity 293

Contents ix

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

Appendix 102 GouyndashChapman theory of the diffuse electrical double-layer 236Problems 238References 242

11 Colloid Stability ndash Part II The DLVO Theory ndash Kinetics of Aggregation 243111 DLVO theory ndash a rapid overview 243112 DLVO theory ndash effect of various parameters 244113 DLVO theory ndash experimental verification and applications 245

1131 Critical coagulation concentration and the Hofmeister series 2451132 DLVO experiments and limitations 247

114 Kinetics of aggregation 2551141 General ndash the Smoluchowski model 2551142 Fast (diffusion-controlled) coagulation 2551143 Stability ratio W 2551144 Structure of aggregates 257

115 Concluding remarks 264Problems 265References 268

12 Emulsions 269121 Introduction 269122 Applications and characterization of emulsions 269123 Destabilization of emulsions 272124 Emulsion stability 273125 Quantitative representation of the steric stabilization 275

1251 Temperature-dependency of steric stabilization 2761252 Conditions for good stabilization 277

126 Emulsion design 278127 PIT ndash Phase inversion temperature of emulsion based on non-ionic emulsifiers 279128 Concluding remarks 279Problems 280References 282

13 Foams 283131 Introduction 283132 Applications of foams 283133 Characterization of foams 285134 Preparation of foams 287135 Measurements of foam stability 287136 Destabilization of foams 288

1361 Gas diffusion 2891362 Film (lamella) rupture 2901363 Drainage of foam by gravity 291

137 Stabilization of foams 2931371 Changing surface viscosity 2931372 Surface elasticity 293

Contents ix

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

1373 Polymers and foam stabilization 2951374 Additives 2961375 Foams and DLVO theory 296

138 How to avoid and destroy foams 2961381 Mechanisms of antifoamingdefoaming 297

139 Rheology of foams 2991310 Concluding remarks 300Problems 301References 302

14 Multicomponent Adsorption 303141 Introduction 303142 Langmuir theory for multicomponent adsorption 304143 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306144 Multicomponent potential theory of adsorption (MPTA) 312145 Discussion Comparison of models 315

1451 IAST ndash literature studies 3151452 IAST versus Langmuir 3151453 MPTA versus IAST versus Langmuir 317

146 Conclusions 317Acknowledgments 319Appendix 141 Proof of Equations 1410ab 319Problems 319References 320

15 Sixty Years with Theories for Interfacial Tension ndash Quo Vadis 321151 Introduction 321152 Early theories 321153 van OssndashGood and Neumann theories 331

1531 The two theories in brief 3311532 What do van OssndashGood and Neumann say about their own theories 3331533 What do van OssndashGood and Neumann say about each otherrsquos theories 3341534 What do others say about van OssndashGood and Neumann theories 3351535 What do we believe about the van OssndashGood and Neumann theories 338

154 A new theory for estimating interfacial tension using the partial solvation parameters(Panayiotou) 339

155 Conclusions ndash Quo Vadis 344Problems 345References 349

16 Epilogue and Review Problems 352Review Problems in Colloid and Surface Chemistry 353

Index 358

x Contents

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

Preface

Colloid and surface chemistry is a subject of immenseimportance and has implications both to our everydaylife and to numerous industrial sectors from paintsand materials to medicine and biotechnologyWhen we observe nature we are impressed by mos-

quitos and other small insects that canwalk onwater butare drawn into the water when detergents (soaps) areadded in their neighbourhood We are fascinated bythe spherical shape of water and even more by the mer-cury droplets that can roll around without wetting any-thingWe know that for the same reasonswe should useplastic raincoats when it is raining We are alsoimpressed by some of natural wonders like the ldquodeltardquocreated by rivers when they meet the sea and the non-sticky wings and leaves of butterflies lotus and someother insects and plants We are also fascinated by theblue colour of the sky and the red colour of the sunsetWhenwe are at homewe are constantly surrounded

by questions related to colloids or interfaces Wewould like to know how detergents really cleanWhy can we not just use water Can we use the deter-gents at room temperature Why do we often clean athigh temperatures Why do so many products havean expiration date (shelf-life) of a few days or weeksWhy canrsquot milk last for ever And why this ldquomilkyrdquocolour that milk has Is it the same thing with thewell-known drink Ouzo Why does Ouzorsquos colourchange from transparent to cloudy when we addwater And what about salt Why does it have suchlarge effect on foods and on our blood pressureWhy do we so often use eggs for making saucesThose who have visited the famous VASA

museum in Stockholm are impressed by the enor-mous efforts made in preserving this ship which sank400 years ago after it was taken out of the sea Why

was a solution of poly(ethylene glycol) spayed onthe shipOf course similar problems occur in industries that

focus on the development and manufacturing of awide range of products ranging from paints high-techmaterials detergents to pharmaceuticals and foodsIn addition here it is not just curiosity that drivesthe questions Paint industries wish to manufactureimproved coatings that can be applied to many differ-ent surfaces but they should also be environmentallyfriendly eg should be less based on organic solventsand if possible exclusively on water Food companiesare interested in developing healthy tasty but alsolong-lasting food products that appeal to both theenvironmental authorities and the consumer Deter-gent and enzyme companies have worked in recentyears sometimes together to develop improvedcleaning formulations containing both surfactantsand enzymes that can clean much better than beforeworking on more persistent stains at lower tempera-tures and amounts to the benefit of both the environ-ment and our pocket Cosmetics is also big businessMany of creams lotions and other personal care pro-ducts are complex emulsions and the companiesinvolved are interested in optimizing their perfor-mance in all respects and even connecting consu-merrsquos reactions to products characteristicsSome companies often inspired by naturersquos

incredible powers as seen in some plants and insectsare interested in designing surface treatment methodsthat can result in self-cleaning surfaces or self-ironingclothes surfaces that do not need detergents clothesthat do not need ironingThere are many more other questions and applica-

tions Why can we get more oil from underground by

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

injecting surfactants Can we deliver drugs for spe-cial cases in better and controlled waysAll of the above and actually much more have their

explanation and understanding in the principles andmethods of colloid and surface chemistry Such acourse is truly valuable to chemists chemical engi-neers biologists material and food scientists andmany more It is both a multi- and interdisciplinarytopic and as a course it must serve diverse needsand requirements depending on the profile of the stu-dents This makes it an exciting topic to teach but alsoa very difficult one Unfortunately as Woods andWasan (1996) showed in their survey among Amer-ican universities a relatively small number of univer-sities teach the course at all This is a problem asseveral universities try to ldquopressrdquo concepts of colloidand surface chemistry (especially the surface tensioncapillarity contact angle and a few more) into generalphysical chemistry courses This is no good This isno way to teach colloids and interfaces This excitingtopic is a science by itself and deserves at least onefull undergraduate course and of course suitablebooks that can be used as textbooksThis brings us to the second major challenge

which is to have a suitable book for teaching a courseto undergraduate students of a (technical) universityMore than ten years ago we were asked to teach a 5ECTS theory course on colloids and interfaces at theTechnical University of Denmark (DTU) The timeallocated for a typical 5 ECTS point (ECTS = Euro-pean Credit System) course at DTU is one four-hourblock a week during a 13 week semester followed byan examination This course is part of the interna-tional program of our university typically at thestart of MSc studies (7thndash8th semester) and can befollowed by students of different MSc programs(Advanced and Applied Chemistry Chemical andBiochemical Engineering Petroleum Engineering)BSc students towards the end of their studies canalso follow the course In Denmark students submita written anonymous evaluation of the course at theend of semester providing feedback on the teachingmethods and course content including course mate-rial (books used)Our experience from 12 years of teaching the

course is that we found it particularly difficult tochoose a suitable textbook that could fulfil the courserequirements and be appealing to different audiences

and the increasing number of students This mayappear to be a ldquoharsh commentrdquo First of all thereare many specialized books in different areas of col-loid and surface chemistry eg Jonsson et al (2001)on surfactants and Israelachvili (2001) on surfaceforces These and other excellent books are of interestto researchers and also to students as supplementarymaterial but are not suitable ndashand we do not think theywere meant by these authors to be ndash as a stand-alonetextbook for a general colloid and surface chemistrycourse Then there are some books for exampleHunter (1993) and Barnes and Gentle (2005) thatfocus either only on colloid or on surface scienceThere are nevertheless several books that more orless target to cover a large part of a standard colloidand surface chemistry curriculum Examples arethose written by Shaw (1992) Goodwin (2004)Hamley (2000) Myers (1991) and Pashley and Kara-man (2004) Some of these could and are indeed usedas textbooks for colloid and surface chemistrycourses Each of these books has naturally theirown strengths and weaknesses We have reportedour impressions and those of our students on the text-books which we have used in the course over theyears in a previous publication (Kontogeorgis andVigild 2009) where we also discuss other aspectsof teaching colloids and interfacesWhat we can state somewhat generally is that

unlike other disciplines of chemical engineering(which we knowwell both of us being chemical engi-neers) we lack in colloid and surface chemistry whatwe could call ldquoclassical stylerdquo textbooks and with anapplied flavour In other fields of chemical engineer-ing eg unit operations thermodynamics reactionengineering and process control there are textbookswith a clear structure and worked out examples alongwith theory and numerous exercises for class orhomework practice We could not generalize thatldquoall is well donerdquo in the textbooks for so many differ-ent disciplines but we do see in many of the classicaltextbooks for other disciplines many common fea-tures that are useful to teachers and of course alsoto students As the structure in several of these disci-plines and their textbooks is also rather establishedthings appear to be presented in a more or less smoothand well-structured wayWe felt that many of these elements were clearly

missing from existing textbooks in colloid and

xii Preface

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

surface chemistry and this book makes an attempt tocover this gap Whether we succeed we cannot say apriori but the positive comments and feedback fromthe students to whom parts of this material has beenexposed in draft form over the years is a positive signThus this book follows the course we have taught

ourselves and we hope that the content and stylemay be appealing to others as well both colleaguesand students We would like to present the mainelements of this book in two respects (i) contentand (ii) styleFirst of all the book is divided approximately

equally into a surface and a colloid chemistrypart although the division is approximate due to theextensive interconnection of the two areas The firsttwo chapters are introductory illustrating someapplications of colloids and interfaces and also theunderlying ndash for both colloids and interfaces ndash roleof intermolecular and interparticleintersurfaceforces The next two chapters present the conceptsof surface and interfacial tension as well as theldquofundamentalrdquo general laws of colloid and surfacescience the Young equation for the contact anglethe YoungndashLaplace and Kelvin equations for pres-sure difference and vapor pressure over curvedsurfaces the Harkins spreading coefficient and theGibbs equation for adsorption We also present insome detail in Chapter 3 various estimation methodsfor surface and interfacial tensions with special focuson theories using concepts from intermolecularforces These estimation methods will be used later(Chapter 6) in applications related to wetting andadhesion We hope that already after Chapter 4 itwill have become clear that colloid and surface chem-istry have a few ldquogeneral lawsrdquo and many conceptsand theories which should be used with cautionAnother major result from these early chapters shouldbe the appreciation of the Gibbs adsorption equationas one of the most useful tools in colloid andsurface chemistry This is an equation that can linkadsorption theories two-dimensional equations ofstate (surface pressurendasharea equations) and surfacetensionconcentration equations These will be fullyappreciated later in Chapter 7 where adsorption isdiscussed in detail as well as in Chapter 14 whichdiscusses multicomponent adsorption theoriesAfter Chapters 1ndash4 comes the discussion of sur-

factants (Chapter 5) solid surfaces with wetting and

adhesion (Chapter 6) and adsorption (Chapter 7) Inthe surfactant chapter we emphasize the structurendashproperty relationships as quantified via the criticalpacking parameter (CPP) and the various factorsaffecting micellization and the values of the criticalmicelle concentration (CMC) The complexity ofsolid surfaces is discussed in Chapter 6 Wettingand adhesion phenomena are analysed with theYoung equation and the theories presented inChapters 3 and 4 but several practical aspects ofadhesion are discussed as well Chapter 7 providesa unified discussion of the adsorption at variousinterfaces Thus the similarities and differences(both in terms of physics and equations) of theadsorptions at various interfaces gasndashliquidliquidndashliquid liquidndashsolid solidndashgas are shownWe discuss how information from one type ofinterface eg solidndashgas can be used in analysingdata in liquidndashsolidliquid interfaces Finally theadsorption of surfactants and polymers which iscrucial eg in the steric stabilization of colloidsis presented in some detail Quantitative tools likeCPP have also a role hereChapter 8 starts the presentation of colloidal prop-

erties Chapters 8 and 9 discuss the kinetic opticaland rheological properties of colloids and we illus-trate how measurements on these properties can yieldimportant information for the colloidal particles espe-cially their molecular weight and shapeChapters 10 and 11 are devoted entirely to aspects

of colloid stability First the essential concepts of theelectrical and van der Waals forces between colloidparticles are presented with special emphasis on theconcepts of the zeta potential double-layer thicknessand Hamaker constants Then the DLVO theory forcolloidal stability is presented This is a major tool incolloid chemistry and we discuss how stability isaffected by manipulating the parameters of by theclassical DLVO theory Chapter 11 closes with apresentation of kinetics of colloid aggregation andstructure of aggregates Chapters 12 and 13 are aboutemulsions and foams respectively ndash two importantcategories of colloid systems where DLVO and otherprinciples of colloid and surface science are appliedIn this case DLVO is often not sufficient Stericforces and solvation effects are not covered by theclassical DLVO and their role in colloid stability isalso discussed in Chapter 12

Preface xiii

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

Chapter 14 presents three theories that can be usedfor describing multicomponent adsorption This is avery important topic which unfortunately is onlyvery briefly touched upon in most colloid and surfacechemistry books It is also a rather advanced topicwhich may be omitted in a regular course The samecan be said for Chapter 15 which presents in somemore detail compared to previous chapters theoriesfor interfacial tension and their strengths and weak-nesses are discussedFinally we close with a concluding chapter and

some remarks on research aspects in colloid and sur-face chemistryIn terms of style we have attempted to provide a

book for those studentsengineersscientists interestedin a first course about colloids and interfaces We havedecided to cover the most important topics in a genericform rather than emphasizing specific applicationseg of relevance to food or pharmaceuticals Neverthe-less many applications are illustrated via the exercisesand selected case studies Each chapter starts with anintroduction and ends with a conclusion whenneeded with links to what will be seen next The basicequations are presented in the main text but to avoidldquofocusing on the trees and losing the forestrdquo the deri-vations of some equations are whenwe feel necessaryadded as appendices in the corresponding chaptersSome of these derivations eg those in Chapters 410 and 14 require advanced knowledge of thermody-namics but our aim is to have the main principles andapplications of colloids and interfaces understood alsoby those students who do not have extensive back-ground in thermodynamics or electrochemistry Wehave included several worked-out examples dispersedin the various chapters and many exercises at the end(with answers in the book website) A full solutionmanual is available to instructors from the authorsWe have deliberately selected a large variety of prob-lem types which illustrate different aspects of the the-ory but also a variety of calculation techniques Thusthe problems vary from simple calculations ndash demon-strations of the general laws of the applicability of the-ories ndash to derivations problems from industrial casestudies and a range of combinedreview problemswhich are presented at the end of the bookWe have decided largely because we had to draw a

line with respect to book size and purpose at some

point to limit this book on theoretical aspects withoutextensive discussions of experimental equipment andtechniques used in colloid and surface chemistryExperiments are extremely important for colloidsand interfaces and fortunately certain key propertiescan be readily measured Even though we do not dis-cuss them extensively we believe however that it isimportant for the student to know which propertiescan indeed be measured and which cannot ndash and forwhich theories are very important A comprehensivetable for this is included in Chapter 1We mentioned that we tried to ldquowrite a book with a

purposerdquo to balance theory and applications to pres-ent the basic principles of colloid and surface chem-istry in an easy to understand way suitable forstudents and beginners in the field and with theapplied flavour in mind But we are not aware ifwe have succeeded We certainly tried and it has beenenjoyable for us to write a book in this way and onthis very exciting topicIf part of this excitement is passed to our readers

students colleagues and engineers we have certainlysucceededWe wish to thank many colleagues for their contri-

bution to this book We are particularly grateful toProfessor Martin E Vigild who participated togetherwith us in the teaching of the course on ldquocolloid andsurface chemistryrdquo over many years and his influenceand input is to be found in many places in this bookFinally we would like to thank The Hempel Foun-

dation for financial support of this book project Thishas enabled us to hire one of our former studentsEmil Kasper Bjoslashrn to help us prepare many of thefigures in the book

Georgios M Kontogeorgis and Soslashren KiilDTU Chemical Engineering

Copenhagen Denmark February 2015

References

GT Barnes and IR Gentle 2005 Interfacial Science ndashAnIntroduction Oxford University Press

J Goodwin 2004 Colloids and Interfaces with Surfactantsand Polymers An Introduction John Wiley amp Sons IncChichester

xiv Preface

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

I Hamley 2000 Introduction to Soft Matter PolymersColloids Amphiphiles and Liquid Crystals JohnWiley amp Sons Inc Chichester

P C Hiemenz and R Rajagopalan 1997 Principles ofColloid and Surface Science 3rd edn Marcel DekkerNew York

R J Hunter 1993 Introduction to Modern Colloid ScienceOxford Science

J Israelachvilli 2011 Intermolecular and Surface Forces3rd edn Academic Press

B Jonsson B Lindman K Holmberg B Kronberg 2001Surfactants and Polymers in Aqueous Solution JohnWiley amp Sons Inc Chichester

GM Kontogeorgis and ME Vigild 2009 Challenges inteaching ldquoColloid and Surface Chemistryrdquo A DanishExperience Chem Eng Educ 43(2) 1

DMyers 1991Surfaces Interfaces andColloids Principlesand Applications VCH Weinheim

R M Pashley and M E Karaman Applied Colloid andSurface Chemistry John Wiley amp Sons Ltd Chichester2004

D Shaw 1992 Introduction to Colloid amp SurfaceChemistry 4th edn Butterworth-Heinemann

DR Woods and DT Wasan 1996 Teaching colloid andsurface phenomena Chem Eng Educ 190ndash197

Preface xv

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

Useful Constants

Acceleration of gravity g = 98066 m sndash2

Avogadro Number NA = 6022 times 1023 molndash1

Boltzmannrsquos constant kB = 1381 times 10ndash23 J Kndash1

Relative permittivity (or dielectric constant) of waterat 20 C = 802

Relative permittivity (or dielectric constant) of waterat 25 C = 785

Dielectric permittivity of vacuum εo = 8854 times10ndash12 C2 Jndash1 mndash1

Dipole moment unit 1 D(ebye) = 3336 times 10ndash30 C mElectronic (elementary) charge e = 1602 times 10ndash19 CIdeal gas constant Rig = 8314 J Kndash1 molndash1 (= NAkB)Ideal gas volume V = 22414 cm3 molndash1 = 22414 times10ndash2m3molndash1 =22414L molndash1 (at stp 0 C1 atm)

ldquoNaturalrdquo kinetic energy kBT = 412 times 10ndash21 J (298 K)Planckrsquos constant h = 6626 times 10ndash34 J sViscosity of water at 20 C 10ndash3 N s mndash2 = 10ndash3 kgmndash1 sndash1

Viscosity of water at 25 C 89 times 10ndash4 N s mndash2 =89 times 10ndash4 kg mndash1 sndash1

Important unit relationships

N = J mndash1 = kg m sndash2

J = N m = kg m2 sndash2

J = kg m2 sndash2

Pa = N mndash2

V = J Cndash1

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

Symbols and Some Basic Abbreviations

Latin

A surface area m2

A A123A121A11 A22

Hamaker constants J

Aeff effective Hamaker constant JΔA change in surface area m2

AB acid-base (interactions concept)A0 area occupied by a gas molecule m2

Aspec specific surface area typically in m2ga energy parameter in two- or three-dimen-

sional equations of statea acceleration ms2

a0 area of the head of a surfactant mole-cule m2

B parameter in the Langmuir equationB1 first Virial coefficient m3kgB2 second Virial coefficient m6(kg mol)b co-volume parameter in two- or three-

dimensional equations of stateCc molar concentration (often in molL or

molm3) or concentration (in general)C parameter in the BET equationCCC critical coagulation concentration molLCFT critical flocculation temperature KCMC critical micelle concentration molLCPP critical packing parameterddp (particle) diameter (and d can also be

distance) mD diffusion coefficient m2sDo diffusion coefficient of equivalent unsol-

vated spheres m2sE electric field strength VME elasticity Jm2 or mNm

E entry coefficient Jm2 or mNme electronic (unit) charge CEO ethylene oxideF foam numberF force NFV viscous force Nf friction(al) coefficient kgsf0 friction(al) coefficient of unsolvated

sphere kgsfRPM rounds per minute (centrifuge) minminus1

g acceleration of gravity ms2

hc critical rupture thickness mH distance between two particles or sur-

faces or films mHB hydrogen bondshydrogen bondingHLB Hydrophilic-lipophilic balanceHSP Hansen solubility parameter (calcm3)12

I ionization potential JI ionic strength molm3

IEP isoelectric pointKL equilibrium adsorption constant m3molKow octanol-water partition coefficientk parameter in the Langmuir equationkB Boltzmann constant JKk2

o rate constant m3(numbers s)l parameter in the HansenBeerbower

equationlc length of a surfactant molecule mLA Lewis acidLB Lewis baseM molar mass (molecular weight) kgmolMW molecular weight kgmolm mass (of colloid particles) kgnσi number of molecules at surface

numbersm2

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

n refractive indexn molar amount moln number of particles per volume mminus3

no initial number of particles per vol-ume mminus3

NA Avogadro number 60225 times 1023 mole-culesmol=molminus1

Nagg Aggregation (or aggregate) number of amicellar structure

[P] ParachorP (vapour) pressure PaPsatPo equilibrium vapour pressure over a flat

surface (ldquoordinaryrdquo vapour pressure) PaPZC point of zero chargePIT phase inversion temperature KRig ideal gas constant 8314 J(mol K)R particle of drop radius mR Hansen radius of solubility (calcm3)12

Ro initial radius of bubble mRg radius of gyration mRf roughness factorRf horizontal film length mR radius of curved surface (spherical parti-

cle droplet bubble) mRep particle Reynolds numberr intermolecular distance mS Harkins spreading coefficient Nm or

mNmSeq solubility of gas in liquid mol(m3 Pa)s solubility molLs sedimentation coefficient sSDS sodium dodecyl sulphateT temperature Kt time st plate thickness mtfrac12 half life sTbr TTb (Tb = boiling temperature)V molar volume m3molV volume per g of solid m3gV potential energy (F=minusdVdH) J or Jm2

VA attractive potential energy J or Jm2

VR repulsive potential energy J or Jm2

Vm maximum volume occupied by a gas (inadsorption in a solid) cm3g

Vmax maximum value of potential energy J orJm2

Vg gas volume at standard T amp P conditions(=22414 cm3mol)

vav average drainage velocity msVF volume of foam m3

VL volume of liquid m3

W work JW stability ratiox mole fractionx distance (eg in centrifuge) mx Brownian end-to-the-end distance mu velocity (of a colloid particle) msQ quadrupole momentw weight fractionvdW van der Waals (forces)z zi ionic valency (including sign)

Greek

α0 electronic polarizability C m2 Vminus1

β parameter in the Zisman equationγ surface or interfacial tension Nm or Jm2

γinfin infinite dilution activity coefficientγo water (solvent) surface tension Nm or Jm2

Γi adsorption of compound (i) molgΓmax maximum adsorption molgδ solubility parameter (calcm3)12

δ adsorbed layer thickness mδ film (lamella) thickness mΔP pressure difference across a curved surface

capillary pressure PaΔG Gibbs energy change (and of micellization)

JmolΔh height change (osmotic pressure) mΔH Enthalpy change (and of micellization)

JmolΔHvap Enthalpy of vaporization JmolΔS Entropy change (and of micellization)

Jmolε0 permittivity of free space (vacuum)

8854 10minus12 C2 Jminus1 mminus1

ε relative permittivity (dielectric constant)ζ zeta potential Vη viscosity (of dispersion medium) kg(m s)ηo viscosity of particle-free medium kg(m s)ηr relative viscosity

xviii Symbols and Some Basic Abbreviations

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

η number of particles per unit volume mminus3

η0 start number of particles per unit vol-ume mminus3

ϑ contact angleθ theta temperature Kκminus1 Debye length (double-layer thickness) mμ electrophoretic mobility m2 Vminus1 sminus1

μ dipole moment C mπ surface pressure (=γwminusγ) Nm or mNmπsv spreading pressure (=γsminusγsv) Nm or mNmπΠ osmotic pressure Paρ (molar) density (molm3) or number densityρL density of liquid kgm3

σ surfaceσ shear stress Nm2

σo charge density Cm2

φ correction parameter in the Girifalco-Goodequation

φG volume fraction of gasφL volume fraction of liquidψ0 surface potential Vω angular acceleration sminus1

Superscripts and subscripts

A attractionattractiveAB acidbase interactionsadhA adhesionads adsorptioncoh cohesioncrit critical (in critical surface tension different

from critical pointc criticald dispersiondw dirt-waterds dirt-solideff effectiveexp experimentalEO ethoxylate groupi gas solid or liquid in expressions for surface

or interfacial tensions

ind inductionj gas solid or liquid in expressions for surface

or interfacial tensionsij gasliquid liquidliquid liquidsolid or

solidsolid in expressions for interfacialtension

g gash hydrogen bondingHg mercurylL liquidlg liquid-gasLW Londonvan der Waalsm mixturem metallic bondingforcesmax maximummix mixingo oil (in the ldquobroaderrdquo sense used in colloid

and surface science)OA oil-air interfaceOW oil-water interface[P] parachorp polar or particleR repulsionrepulsiver reduced (eg Tr=TTc)sat saturateds solids stericsd solid-dirtspec specific (forcescontribution)sl solid-liquid interfacesurf surfactantspec specific (non-dispersion) effects eg due to

polar hydrogen bonding metallichellipsw solid-watersv solid-vapor (with vapor coming from liquid)theor theoreticalw waterWA water-air interface+ acid effects (van Oss-Good theory)minus base effects (van Oss-Good theory)1 particle or droplet2 medium

Symbols and Some Basic Abbreviations xix

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

About the Companion Web Site

This book is accompanied by a companion website

wwwwileycomgokontogeorgiscolloid

This website includes

bull PowerPoint slides of all figures from the book for downloadingbull Solutions to problems

1Introduction to Colloid and

Surface Chemistry

11 What are the colloids and interfacesWhy are they important Why do westudy them together

Colloid and surface chemistry is a core subjectof physical chemistry It is a highly interdisciplinarysubject of interest to diverse fields of science andengineering (pharmaceuticals food cosmetics deter-gents medicine and biology up to materials andmicroelectronics just to mention a few) Beingchallenging to teach it is often either incorporatedor presented very briefly in general physical che-mistry courses or even worse completely neglected(Panayiotou 1998)Colloidal systems have a minimum of two compo-

nents Colloidal dispersions are systems of particlesor droplets with the ldquoright dimensionsrdquo (the dispersedphase) which are dispersed in a medium (gas liquidor solid) The medium is called the continuousphase which is usually in excess But which arethe ldquoright dimensionsrdquo The particles or droplets have

dimensions (or one key dimension) between (typi-cally) 1 nm and 1 μm and their special properties arisefrom the large surfaces due to precisely these dimen-sions (Figure 11)However sometimes even larger particles with

diameters up to 10 or even up to 50 micrometre(μm) eg in emulsions or very small particles assmall as 5 times 10ndash10 m can present colloidal characterThus despite the above definition it is sometimesstated that ldquoIf it looks like and if it acts like a colloidit is a colloidrdquoColloids are characterized by their many interest-

ing properties (eg kinetic or optical) as well as byobserving their stability over timeThe characteristic properties of colloidal systems

are due to the size of the particles or droplets (iethe dispersed phase) and not to any special natureof the particles However their name is attributedto Thomas Graham (Figure 12) who was studyingglue-like (gelatinous or gum-like polymeric) solu-tions (from the Greek word for glue which is ldquocollardquo)

Introduction to Applied Colloid and Surface Chemistry First Edition Georgios M Kontogeorgis and Soslashren Kiilcopy 2016 John Wiley amp Sons Ltd Published 2016 by John Wiley amp Sons LtdCompanion website wwwwileycomgokontogeorgiscolloid

Many colloidal systems like milk are easily identi-fied by their colour or more precisely their non-transparent appearance (Figure 13) The opticalproperties of colloids are very important also in theircharacterization and study of their stability ndash asdiscussed in later chaptersColloidal particles (or droplets) are not always

spherical They can have various shapes (eg spher-ical and rod- or disk-like) as shown in Figure 14Proteinic and polymeric molecules are usually large

enough to be defined as colloid particles Moreovertheir shape may be somewhat affected by solvation(hydration) phenomena where solvent moleculesbecome ldquoattachedrdquo to them and influence their finalproperties Solutions of proteins and polymers maybe stable and they are classified as lyophilic colloidsMany colloidal particles (eg Au or AgI) are (near)spherical but others are not For example proteinsare often ellipsoids while many polymers are randomcoils

Figure 12 Thomas Graham (1805ndash1869) the pioneer in the study of colloidal systems used the term ldquocolloidsrdquoderived from the Greek word for glue (ldquocollardquo) He thought that their special properties were due to the nature of thecompounds involved Later it was realized that the size of particles (of the ldquodispersed phaserdquo as we call it) is solelyresponsible for the special properties of colloidal systems (Right) T Graham H4070106 Courtesy of Science PhotoLibrary

Smallmolecules

10ndash10m

10ndash9

10ndash7 10ndash4cm

Colloidal domain

hellip

Nano-metre

Micro-metre

Milli-metre

10ndash6 10ndash3

Micellespolymer

coils

Pigmentparticles

(Aring)

Finedrops

Fibres(hair)

Capsuleyarnpaintlayer

Figure 11 Scales in colloid and surface science Typically colloidal particles have one key dimension between1 nm and 1 μm (micrometre) Adapted from Wesselingh et al (2007) with permission from John Wiley amp Sons Ltd

2 Introduction to Applied Colloid and Surface Chemistry

111 Colloids and interfaces

What about surfaces and interfaces Colloidal systemsare composed of small particles dispersed in amediumThe fact that these particles have such small dimen-sions is the reason that a huge surface (interfacial) areais created Their high interfacial area is the reason whycolloidal systems have special properties and also whywe study colloids and interfaces together As shown inFigure 15 the surfaces or interfaces are sometimes

considered to be ldquosimplyrdquo the rdquodividing linesrdquo betweentwo different phases although they are not really linesthey do have a certain thickness of a few Aring (of theorder of molecular diameters)

Scale

100 Aring

Egg albumin42 000

γ-globulin156 000

Albumin69 000Hemoglobin

68 000

Insulin36 000

β-lactoglobulin40 000

β-globulin90 000

Fibrinogen400 000

β-lipoprotein1 300 000

α-lipoprotein200 000

Glucose

Figure 14 Different shapes of colloid particles with molecular weights provided in g molndash1 Pr J L Onclev HarvardMedical School

Figure 13 A non-colloidal (water) and a colloidal liq-uid system (milk)

GAS

Liquid ALiquid ALiquid A

Liquid B

SolidSolid

Solid BSolid B

Solid ASolid A

Liquid-gasinterface

Liquid-liquidinterface

Solid-gasinterface

Solid-solidinterface

Interfacialtension

Interfacialtension

Solid-liquidinterface

Surfacetension

Figure 15 Surfaces and interfaces involving solidsliquids and gases An interface has a thickness of afew aringngstroslashm (1 Aring = 10ndash10 m)

1 Introduction to Colloid and Surface Chemistry 3

We often use the term rdquosurfacesrdquo if one of thephases is a gas and the term ldquointerfacerdquo betweenliquidndashliquid liquidndashsolid and solidndashsolid phasesAll of these interfaces are important in colloid andsurface science in the understanding manufacturingor in the application of colloidal products Howeverthere are many applications in surface science whichare not directly related to colloidsThe huge interface associated with colloids is the

reason why colloid and surface chemistry are oftenstudied together Colloidal dimensions imply that thereare numerous surface molecules due to the large sur-faces present For example 1 litre of a latex paint sus-pension containing 50 solids with a particle size of02 μm has a total particle surface area of 15 000 m2However to form such huge interfaces eg by disper-sing water in the form of droplets in an oil we need ldquoto

do a lot of workrdquo This work remains in the system andthus the dispersed phase is not in the lowest energycondition There is a natural tendency for droplets tocoalesce and for particles to aggregate To maintainthe material in the colloidal state we need to manipu-late the various forces between particlesdroplets andachieve stability Colloidal stability is one of the mostimportant topics in colloid chemistry

12 Applications

Colloids and interfaces are present and of importancein many (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues (Figure 16) These are

Colloid and surfacechemistry - some

applicationsMaterials and

nanotechnology

Paints and coatings

Chemical industry

Glues (adhesives) lubricants

Nanoporous materials

Cell membranes

Oil recovery

Oil industry

Biotechnology

Food scienceFood emulsions and dispersions

Environment

Air chemistry aerosols

Water purification

Natural phenomena soilstructure

Separations

Adsorption

Membranes

Filtering

Flotation

Porous materials

Capillary condensation

Lung surfactant

Drug delivery

Protein analysis (MW)

Pharmaceutical emulsions

Proteins and surfactants indetergents

Surfaces with uniqueproperties (self cleaning)

Surface manipulation andanalysis

Electronics semiconductors

Extreme applications(space)

Detergents-cleaning

Photo-emulsions

Catalysts-catalysis

Mineral processing and separations in mining industry

ndash

ndash

ndash

ndash

ndash

ndash

ndash

Figure 16 Selected applications of colloid and surface chemistry

4 Introduction to Applied Colloid and Surface Chemistry

some examples of what we call ldquostructured productsrdquoMost of these products are colloidal systems eg milk(liquid emulsion) or paint (emulsions or dispersions)The production andor use of many colloidal-basedproducts involve knowledge of surface science egthe adhesion of glues and paints or cleaning with deter-gentsMost of these everyday ldquoconsumerrdquo products arerather complex in the sense that they contain manycomponents eg polymers solids surfactants andwater or other solvents As alreadymentioned colloidsand interfaces are linked and they are best studiedtogether Figure 17 shows some interrelations

13 Three ways of classifying the colloids

Colloids (or colloidal dispersions) can be classifiedaccording to the state of the dispersed phase and

the dispersion medium (gas liquid solid) seeTable 11 or according to their stability The mostwell-known colloids are emulsions (both phases areliquids) dispersions (solid particles in a liquidmedium) foams (gases in liquids) liquids in solids(gels) and aerosols (liquids or solids in a gas)The common colloidal dispersions (eg food

or paint) are thermodynamically unstable while asso-ciation colloids (surfactants) and polymerproteinsolutions are thermodynamically stable In additionthere can be multiple or complex colloids whichare combinations of the above eg dispersion emul-sion surfactants andor polymers in a continuousphase Finally network colloids also called gelsare sometimes considered to be a separate categoryLyophobic (ie solvent hating) colloids are those

in which the dispersoid (dispersed object) constitutesa distinct phase while lyophilic colloids refer to

ndash

ndash

Applications ofcolloids amp interfaces

Cosmetics

Paints glues adhesives

Food (colloids)

Pharmaceuticals

Design of novel materials

CleaningNovel protein separationprocesses

Molecular weight ofbiomolecules

Biological membranes

Protein aggregation anddiseases

Lubrication

Water resources (cleaning andcontrol of evaporation)

Catalysis

Ceramics eg in fuel cells

Mining

Paper

Agrochemicals

Detergents

Products

ProcessesBiotechnologyndash

Figure 17 A few applications of colloids and interfaces related to various types of products and processes

1 Introduction to Colloid and Surface Chemistry 5

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

Many colloidal systems like milk are easily identi-fied by their colour or more precisely their non-transparent appearance (Figure 13) The opticalproperties of colloids are very important also in theircharacterization and study of their stability ndash asdiscussed in later chaptersColloidal particles (or droplets) are not always

spherical They can have various shapes (eg spher-ical and rod- or disk-like) as shown in Figure 14Proteinic and polymeric molecules are usually large

enough to be defined as colloid particles Moreovertheir shape may be somewhat affected by solvation(hydration) phenomena where solvent moleculesbecome ldquoattachedrdquo to them and influence their finalproperties Solutions of proteins and polymers maybe stable and they are classified as lyophilic colloidsMany colloidal particles (eg Au or AgI) are (near)spherical but others are not For example proteinsare often ellipsoids while many polymers are randomcoils

Figure 12 Thomas Graham (1805ndash1869) the pioneer in the study of colloidal systems used the term ldquocolloidsrdquoderived from the Greek word for glue (ldquocollardquo) He thought that their special properties were due to the nature of thecompounds involved Later it was realized that the size of particles (of the ldquodispersed phaserdquo as we call it) is solelyresponsible for the special properties of colloidal systems (Right) T Graham H4070106 Courtesy of Science PhotoLibrary

Smallmolecules

10ndash10m

10ndash9

10ndash7 10ndash4cm

Colloidal domain

hellip

Nano-metre

Micro-metre

Milli-metre

10ndash6 10ndash3

Micellespolymer

coils

Pigmentparticles

(Aring)

Finedrops

Fibres(hair)

Capsuleyarnpaintlayer

Figure 11 Scales in colloid and surface science Typically colloidal particles have one key dimension between1 nm and 1 μm (micrometre) Adapted from Wesselingh et al (2007) with permission from John Wiley amp Sons Ltd

2 Introduction to Applied Colloid and Surface Chemistry

111 Colloids and interfaces

What about surfaces and interfaces Colloidal systemsare composed of small particles dispersed in amediumThe fact that these particles have such small dimen-sions is the reason that a huge surface (interfacial) areais created Their high interfacial area is the reason whycolloidal systems have special properties and also whywe study colloids and interfaces together As shown inFigure 15 the surfaces or interfaces are sometimes

considered to be ldquosimplyrdquo the rdquodividing linesrdquo betweentwo different phases although they are not really linesthey do have a certain thickness of a few Aring (of theorder of molecular diameters)

Scale

100 Aring

Egg albumin42 000

γ-globulin156 000

Albumin69 000Hemoglobin

68 000

Insulin36 000

β-lactoglobulin40 000

β-globulin90 000

Fibrinogen400 000

β-lipoprotein1 300 000

α-lipoprotein200 000

Glucose

Figure 14 Different shapes of colloid particles with molecular weights provided in g molndash1 Pr J L Onclev HarvardMedical School

Figure 13 A non-colloidal (water) and a colloidal liq-uid system (milk)

GAS

Liquid ALiquid ALiquid A

Liquid B

SolidSolid

Solid BSolid B

Solid ASolid A

Liquid-gasinterface

Liquid-liquidinterface

Solid-gasinterface

Solid-solidinterface

Interfacialtension

Interfacialtension

Solid-liquidinterface

Surfacetension

Figure 15 Surfaces and interfaces involving solidsliquids and gases An interface has a thickness of afew aringngstroslashm (1 Aring = 10ndash10 m)

1 Introduction to Colloid and Surface Chemistry 3

We often use the term rdquosurfacesrdquo if one of thephases is a gas and the term ldquointerfacerdquo betweenliquidndashliquid liquidndashsolid and solidndashsolid phasesAll of these interfaces are important in colloid andsurface science in the understanding manufacturingor in the application of colloidal products Howeverthere are many applications in surface science whichare not directly related to colloidsThe huge interface associated with colloids is the

reason why colloid and surface chemistry are oftenstudied together Colloidal dimensions imply that thereare numerous surface molecules due to the large sur-faces present For example 1 litre of a latex paint sus-pension containing 50 solids with a particle size of02 μm has a total particle surface area of 15 000 m2However to form such huge interfaces eg by disper-sing water in the form of droplets in an oil we need ldquoto

do a lot of workrdquo This work remains in the system andthus the dispersed phase is not in the lowest energycondition There is a natural tendency for droplets tocoalesce and for particles to aggregate To maintainthe material in the colloidal state we need to manipu-late the various forces between particlesdroplets andachieve stability Colloidal stability is one of the mostimportant topics in colloid chemistry

12 Applications

Colloids and interfaces are present and of importancein many (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues (Figure 16) These are

Colloid and surfacechemistry - some

applicationsMaterials and

nanotechnology

Paints and coatings

Chemical industry

Glues (adhesives) lubricants

Nanoporous materials

Cell membranes

Oil recovery

Oil industry

Biotechnology

Food scienceFood emulsions and dispersions

Environment

Air chemistry aerosols

Water purification

Natural phenomena soilstructure

Separations

Adsorption

Membranes

Filtering

Flotation

Porous materials

Capillary condensation

Lung surfactant

Drug delivery

Protein analysis (MW)

Pharmaceutical emulsions

Proteins and surfactants indetergents

Surfaces with uniqueproperties (self cleaning)

Surface manipulation andanalysis

Electronics semiconductors

Extreme applications(space)

Detergents-cleaning

Photo-emulsions

Catalysts-catalysis

Mineral processing and separations in mining industry

ndash

ndash

ndash

ndash

ndash

ndash

ndash

Figure 16 Selected applications of colloid and surface chemistry

4 Introduction to Applied Colloid and Surface Chemistry

some examples of what we call ldquostructured productsrdquoMost of these products are colloidal systems eg milk(liquid emulsion) or paint (emulsions or dispersions)The production andor use of many colloidal-basedproducts involve knowledge of surface science egthe adhesion of glues and paints or cleaning with deter-gentsMost of these everyday ldquoconsumerrdquo products arerather complex in the sense that they contain manycomponents eg polymers solids surfactants andwater or other solvents As alreadymentioned colloidsand interfaces are linked and they are best studiedtogether Figure 17 shows some interrelations

13 Three ways of classifying the colloids

Colloids (or colloidal dispersions) can be classifiedaccording to the state of the dispersed phase and

the dispersion medium (gas liquid solid) seeTable 11 or according to their stability The mostwell-known colloids are emulsions (both phases areliquids) dispersions (solid particles in a liquidmedium) foams (gases in liquids) liquids in solids(gels) and aerosols (liquids or solids in a gas)The common colloidal dispersions (eg food

or paint) are thermodynamically unstable while asso-ciation colloids (surfactants) and polymerproteinsolutions are thermodynamically stable In additionthere can be multiple or complex colloids whichare combinations of the above eg dispersion emul-sion surfactants andor polymers in a continuousphase Finally network colloids also called gelsare sometimes considered to be a separate categoryLyophobic (ie solvent hating) colloids are those

in which the dispersoid (dispersed object) constitutesa distinct phase while lyophilic colloids refer to

ndash

ndash

Applications ofcolloids amp interfaces

Cosmetics

Paints glues adhesives

Food (colloids)

Pharmaceuticals

Design of novel materials

CleaningNovel protein separationprocesses

Molecular weight ofbiomolecules

Biological membranes

Protein aggregation anddiseases

Lubrication

Water resources (cleaning andcontrol of evaporation)

Catalysis

Ceramics eg in fuel cells

Mining

Paper

Agrochemicals

Detergents

Products

ProcessesBiotechnologyndash

Figure 17 A few applications of colloids and interfaces related to various types of products and processes

1 Introduction to Colloid and Surface Chemistry 5

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

111 Colloids and interfaces

What about surfaces and interfaces Colloidal systemsare composed of small particles dispersed in amediumThe fact that these particles have such small dimen-sions is the reason that a huge surface (interfacial) areais created Their high interfacial area is the reason whycolloidal systems have special properties and also whywe study colloids and interfaces together As shown inFigure 15 the surfaces or interfaces are sometimes

considered to be ldquosimplyrdquo the rdquodividing linesrdquo betweentwo different phases although they are not really linesthey do have a certain thickness of a few Aring (of theorder of molecular diameters)

Scale

100 Aring

Egg albumin42 000

γ-globulin156 000

Albumin69 000Hemoglobin

68 000

Insulin36 000

β-lactoglobulin40 000

β-globulin90 000

Fibrinogen400 000

β-lipoprotein1 300 000

α-lipoprotein200 000

Glucose

Figure 14 Different shapes of colloid particles with molecular weights provided in g molndash1 Pr J L Onclev HarvardMedical School

Figure 13 A non-colloidal (water) and a colloidal liq-uid system (milk)

GAS

Liquid ALiquid ALiquid A

Liquid B

SolidSolid

Solid BSolid B

Solid ASolid A

Liquid-gasinterface

Liquid-liquidinterface

Solid-gasinterface

Solid-solidinterface

Interfacialtension

Interfacialtension

Solid-liquidinterface

Surfacetension

Figure 15 Surfaces and interfaces involving solidsliquids and gases An interface has a thickness of afew aringngstroslashm (1 Aring = 10ndash10 m)

1 Introduction to Colloid and Surface Chemistry 3

We often use the term rdquosurfacesrdquo if one of thephases is a gas and the term ldquointerfacerdquo betweenliquidndashliquid liquidndashsolid and solidndashsolid phasesAll of these interfaces are important in colloid andsurface science in the understanding manufacturingor in the application of colloidal products Howeverthere are many applications in surface science whichare not directly related to colloidsThe huge interface associated with colloids is the

reason why colloid and surface chemistry are oftenstudied together Colloidal dimensions imply that thereare numerous surface molecules due to the large sur-faces present For example 1 litre of a latex paint sus-pension containing 50 solids with a particle size of02 μm has a total particle surface area of 15 000 m2However to form such huge interfaces eg by disper-sing water in the form of droplets in an oil we need ldquoto

do a lot of workrdquo This work remains in the system andthus the dispersed phase is not in the lowest energycondition There is a natural tendency for droplets tocoalesce and for particles to aggregate To maintainthe material in the colloidal state we need to manipu-late the various forces between particlesdroplets andachieve stability Colloidal stability is one of the mostimportant topics in colloid chemistry

12 Applications

Colloids and interfaces are present and of importancein many (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues (Figure 16) These are

Colloid and surfacechemistry - some

applicationsMaterials and

nanotechnology

Paints and coatings

Chemical industry

Glues (adhesives) lubricants

Nanoporous materials

Cell membranes

Oil recovery

Oil industry

Biotechnology

Food scienceFood emulsions and dispersions

Environment

Air chemistry aerosols

Water purification

Natural phenomena soilstructure

Separations

Adsorption

Membranes

Filtering

Flotation

Porous materials

Capillary condensation

Lung surfactant

Drug delivery

Protein analysis (MW)

Pharmaceutical emulsions

Proteins and surfactants indetergents

Surfaces with uniqueproperties (self cleaning)

Surface manipulation andanalysis

Electronics semiconductors

Extreme applications(space)

Detergents-cleaning

Photo-emulsions

Catalysts-catalysis

Mineral processing and separations in mining industry

ndash

ndash

ndash

ndash

ndash

ndash

ndash

Figure 16 Selected applications of colloid and surface chemistry

4 Introduction to Applied Colloid and Surface Chemistry

some examples of what we call ldquostructured productsrdquoMost of these products are colloidal systems eg milk(liquid emulsion) or paint (emulsions or dispersions)The production andor use of many colloidal-basedproducts involve knowledge of surface science egthe adhesion of glues and paints or cleaning with deter-gentsMost of these everyday ldquoconsumerrdquo products arerather complex in the sense that they contain manycomponents eg polymers solids surfactants andwater or other solvents As alreadymentioned colloidsand interfaces are linked and they are best studiedtogether Figure 17 shows some interrelations

13 Three ways of classifying the colloids

Colloids (or colloidal dispersions) can be classifiedaccording to the state of the dispersed phase and

the dispersion medium (gas liquid solid) seeTable 11 or according to their stability The mostwell-known colloids are emulsions (both phases areliquids) dispersions (solid particles in a liquidmedium) foams (gases in liquids) liquids in solids(gels) and aerosols (liquids or solids in a gas)The common colloidal dispersions (eg food

or paint) are thermodynamically unstable while asso-ciation colloids (surfactants) and polymerproteinsolutions are thermodynamically stable In additionthere can be multiple or complex colloids whichare combinations of the above eg dispersion emul-sion surfactants andor polymers in a continuousphase Finally network colloids also called gelsare sometimes considered to be a separate categoryLyophobic (ie solvent hating) colloids are those

in which the dispersoid (dispersed object) constitutesa distinct phase while lyophilic colloids refer to

ndash

ndash

Applications ofcolloids amp interfaces

Cosmetics

Paints glues adhesives

Food (colloids)

Pharmaceuticals

Design of novel materials

CleaningNovel protein separationprocesses

Molecular weight ofbiomolecules

Biological membranes

Protein aggregation anddiseases

Lubrication

Water resources (cleaning andcontrol of evaporation)

Catalysis

Ceramics eg in fuel cells

Mining

Paper

Agrochemicals

Detergents

Products

ProcessesBiotechnologyndash

Figure 17 A few applications of colloids and interfaces related to various types of products and processes

1 Introduction to Colloid and Surface Chemistry 5

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

We often use the term rdquosurfacesrdquo if one of thephases is a gas and the term ldquointerfacerdquo betweenliquidndashliquid liquidndashsolid and solidndashsolid phasesAll of these interfaces are important in colloid andsurface science in the understanding manufacturingor in the application of colloidal products Howeverthere are many applications in surface science whichare not directly related to colloidsThe huge interface associated with colloids is the

reason why colloid and surface chemistry are oftenstudied together Colloidal dimensions imply that thereare numerous surface molecules due to the large sur-faces present For example 1 litre of a latex paint sus-pension containing 50 solids with a particle size of02 μm has a total particle surface area of 15 000 m2However to form such huge interfaces eg by disper-sing water in the form of droplets in an oil we need ldquoto

do a lot of workrdquo This work remains in the system andthus the dispersed phase is not in the lowest energycondition There is a natural tendency for droplets tocoalesce and for particles to aggregate To maintainthe material in the colloidal state we need to manipu-late the various forces between particlesdroplets andachieve stability Colloidal stability is one of the mostimportant topics in colloid chemistry

12 Applications

Colloids and interfaces are present and of importancein many (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues (Figure 16) These are

Colloid and surfacechemistry - some

applicationsMaterials and

nanotechnology

Paints and coatings

Chemical industry

Glues (adhesives) lubricants

Nanoporous materials

Cell membranes

Oil recovery

Oil industry

Biotechnology

Food scienceFood emulsions and dispersions

Environment

Air chemistry aerosols

Water purification

Natural phenomena soilstructure

Separations

Adsorption

Membranes

Filtering

Flotation

Porous materials

Capillary condensation

Lung surfactant

Drug delivery

Protein analysis (MW)

Pharmaceutical emulsions

Proteins and surfactants indetergents

Surfaces with uniqueproperties (self cleaning)

Surface manipulation andanalysis

Electronics semiconductors

Extreme applications(space)

Detergents-cleaning

Photo-emulsions

Catalysts-catalysis

Mineral processing and separations in mining industry

ndash

ndash

ndash

ndash

ndash

ndash

ndash

Figure 16 Selected applications of colloid and surface chemistry

4 Introduction to Applied Colloid and Surface Chemistry

some examples of what we call ldquostructured productsrdquoMost of these products are colloidal systems eg milk(liquid emulsion) or paint (emulsions or dispersions)The production andor use of many colloidal-basedproducts involve knowledge of surface science egthe adhesion of glues and paints or cleaning with deter-gentsMost of these everyday ldquoconsumerrdquo products arerather complex in the sense that they contain manycomponents eg polymers solids surfactants andwater or other solvents As alreadymentioned colloidsand interfaces are linked and they are best studiedtogether Figure 17 shows some interrelations

13 Three ways of classifying the colloids

Colloids (or colloidal dispersions) can be classifiedaccording to the state of the dispersed phase and

the dispersion medium (gas liquid solid) seeTable 11 or according to their stability The mostwell-known colloids are emulsions (both phases areliquids) dispersions (solid particles in a liquidmedium) foams (gases in liquids) liquids in solids(gels) and aerosols (liquids or solids in a gas)The common colloidal dispersions (eg food

or paint) are thermodynamically unstable while asso-ciation colloids (surfactants) and polymerproteinsolutions are thermodynamically stable In additionthere can be multiple or complex colloids whichare combinations of the above eg dispersion emul-sion surfactants andor polymers in a continuousphase Finally network colloids also called gelsare sometimes considered to be a separate categoryLyophobic (ie solvent hating) colloids are those

in which the dispersoid (dispersed object) constitutesa distinct phase while lyophilic colloids refer to

ndash

ndash

Applications ofcolloids amp interfaces

Cosmetics

Paints glues adhesives

Food (colloids)

Pharmaceuticals

Design of novel materials

CleaningNovel protein separationprocesses

Molecular weight ofbiomolecules

Biological membranes

Protein aggregation anddiseases

Lubrication

Water resources (cleaning andcontrol of evaporation)

Catalysis

Ceramics eg in fuel cells

Mining

Paper

Agrochemicals

Detergents

Products

ProcessesBiotechnologyndash

Figure 17 A few applications of colloids and interfaces related to various types of products and processes

1 Introduction to Colloid and Surface Chemistry 5

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

some examples of what we call ldquostructured productsrdquoMost of these products are colloidal systems eg milk(liquid emulsion) or paint (emulsions or dispersions)The production andor use of many colloidal-basedproducts involve knowledge of surface science egthe adhesion of glues and paints or cleaning with deter-gentsMost of these everyday ldquoconsumerrdquo products arerather complex in the sense that they contain manycomponents eg polymers solids surfactants andwater or other solvents As alreadymentioned colloidsand interfaces are linked and they are best studiedtogether Figure 17 shows some interrelations

13 Three ways of classifying the colloids

Colloids (or colloidal dispersions) can be classifiedaccording to the state of the dispersed phase and

the dispersion medium (gas liquid solid) seeTable 11 or according to their stability The mostwell-known colloids are emulsions (both phases areliquids) dispersions (solid particles in a liquidmedium) foams (gases in liquids) liquids in solids(gels) and aerosols (liquids or solids in a gas)The common colloidal dispersions (eg food

or paint) are thermodynamically unstable while asso-ciation colloids (surfactants) and polymerproteinsolutions are thermodynamically stable In additionthere can be multiple or complex colloids whichare combinations of the above eg dispersion emul-sion surfactants andor polymers in a continuousphase Finally network colloids also called gelsare sometimes considered to be a separate categoryLyophobic (ie solvent hating) colloids are those

in which the dispersoid (dispersed object) constitutesa distinct phase while lyophilic colloids refer to

ndash

ndash

Applications ofcolloids amp interfaces

Cosmetics

Paints glues adhesives

Food (colloids)

Pharmaceuticals

Design of novel materials

CleaningNovel protein separationprocesses

Molecular weight ofbiomolecules

Biological membranes

Protein aggregation anddiseases

Lubrication

Water resources (cleaning andcontrol of evaporation)

Catalysis

Ceramics eg in fuel cells

Mining

Paper

Agrochemicals

Detergents

Products

ProcessesBiotechnologyndash

Figure 17 A few applications of colloids and interfaces related to various types of products and processes

1 Introduction to Colloid and Surface Chemistry 5

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

single-phase solutions of macromolecules or poly-mers Lyophobic colloids are thermodynamicallyunstable These terms describe the tendency of a par-ticle (in general a chemical group or surface) tobecome wettedsolvated by the liquid (=lyo- orhydrophilic in the case of water) Certain colloids likeproteins have an amphiphilic behaviour as there aregroups of both hydrophobic tendency (the hydrocar-bon regions) and hydrophilic nature (the peptidelinkages and the amino and carboxyl groups)The terms hydrophobic and hydrophilic can also be

used for surfaces Both surfaces and colloid particlescan ldquochangerdquo character from hydrophilic to hydropho-bic andvice versa For example cleanglass surfaces arehydrophilic but they can be made hydrophobic by acoating of wax as discussed by Pashley and Karaman(2004) In addition the hydrophobic (hydrocarbon)droplets inanoil-in-water emulsion canbemadehydro-philic by the addition of protein to the emulsion ndash theprotein molecules adsorb onto the droplet surfacesUnstable colloids can be kinetically stable (ie

stable over a limited time period) The stability ofcolloids one of their most important characteristicsis discussed in Chapters 10 and 11

14 How to prepare colloid systems

There are various ways to ldquotrickrdquo particle formationsand create a colloidal system The most importantones are the rdquoaggregationrdquo of molecules or ions and

ldquogrindingrdquo or ldquomillingrdquo methods typically in a millstirrer with the application of shear stress and addingsome dispersants eg surfactants Other methods arebased on the precipitation or the reduction of the sol-ubility of a substance in a solvent such as in the case ofthe well-known Greek drink Ouzo (Figure 18) whose

Table 11 Examples of colloidal systems ie one type of compound eg solid particles or liquiddroplets in a medium Different combinations are possible depending on the phase of the particles(dispersed phase) and the (dispersion) medium they are in Two gas phases will mix on a molec-ular level and do not form a colloidal system

Dispersed phase Dispersion medium Name Examples

Liquid Gas Liquid aerosol Fog mist liquid spraysGas Liquid Foam rdquoChantillyrdquo cream

shaving creamLiquid Liquid Emulsion Milk mayonnaise butterSolid Liquid Dispersion Toothpaste paintsGas Solid Solid foam Expanded polystyreneLiquid Solid Gel PearlSolid Solid Solid dispersion Pigmented plastics bones

Modified from Shaw (1992) Pashley and Karaman (2004) Hiemenz and Rajagopalan (1997) and Goodwin (2009)

Figure 18 Ouzo an example of a colloidal systemThe reduced transparency upon addition of water isdue to the reduction of anise oil solubility in alcohol

6 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

opaque colour when water is added is due to the reduc-tion of the alcohol content In Ouzorsquos standard state(conventional alcohol content) the drink is colourlessbecause the anise oil fully dissolves in the alcoholBut as soon as the alcohol content is reduced (by add-ing water) the essential oils transform into white crys-tals which you cannot see through (like in milkanother classical colloidal system) The same phenom-enon occurs when it is stored in a refrigerator ButOuzo resumes its former state as soon as it is placedat room temperatureTypically the colloids need after their preparation

to be purified eg to remove the electrolytes thatdestabilize them and there are many techniques fordoing that Among the most popular ones are the dial-ysis the ultrafiltration the size exclusion chromatog-raphy (SEC) and the gel permeation chromatography(GPC) The basic separation principle is the size dif-ference between the colloid and the other substancesthat need to be removed

15 Key properties of colloids

Colloidal systems are special and exciting in manyways They have very interesting kinetic rheologi-cal and optical properties (Chapters 8 and 9) whichare important for their characterization (determina-tion of molecular weight and shape) and applicationBut their most important feature is possibly the largesurface area and this is why these systems are oftenunstable (or metastable) The stability of colloidsinvolves the relative balance between the attractivevan der Waals and the repulsive forces the latter areoften due to the electrical charge that most colloidparticles have The van der Waals attractive forcesin colloids are much stronger than those betweenmolecules and lead to aggregation (instability) butthere are (fortunately) also repulsive electricalforces when the particles are charged which rdquohelpstabilityrdquo There are other types of repulsive forceseg steric solvation Manipulating colloidal stabil-ity implies knowing how we can change or influ-ence the various forces especially the van derWaals attractive and the electrical and steric repul-sive forces

We emphasize thus from the start that almost alllyophobic colloids are in reality metastable systemsWhen we use the term ldquostablerdquo colloids throughoutthis book we imply a kinetically stable colloid atsome arbitrary length of time (which can be forexample two days or two years depending on theapplication)

16 Concluding remarks

Colloids and interfaces are present and important inmany (everyday) products and processes rangingfrom food milk and pharmaceuticals to cleaningagents and paints or glues They are intimately linkedand are best studied together Colloids have manyimportant exciting properties of which stability ispossibly the most important Some properties of col-loids and interfaces can be measured while otherscannot and are obtained best via theoriesmodelsAn overview of what can be measured and whatcannot in colloid and surface science is given inAppendix 11Colloids can be classified according to the phase

(gas liquid solid) of the dispersed phase and the dis-persion medium or according to their stability Colloi-dal dispersions are thermodynamically unstablewhile association colloids (surfactants) and poly-merprotein solutions are stable The former are oftencalled lyophobic (hydrophobic if the dispersionmedium is water) and the latter lyophilic (hydro-philic) colloids These terms can be also used forsurfacesCrucial in the study of both colloids and

interfaces is knowledge of the forces betweenmolecules and particles or surfaces and this is dis-cussed next While as explained a strict division isnot possible Chapters 3ndash7 discuss characteristicsand properties of interfaces (surface and interfacialtensions fundamental laws in interfacial phenom-ena wetting amp adhesion surfactants and adsorp-tion) while Chapters 8ndash13 present the kineticrheological and optical properties of colloids aswell as their stability and also a separate discussionof two important colloid categories emulsionsand foams

1 Introduction to Colloid and Surface Chemistry 7

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry

Appendix 11

Table A1 Overview of what can be measured and what can be calculated in the area of colloid and surfacechemistry

Property Can wemeasure it (How) Can we estimate it (How) Comments ndash applications

Surface tension of pureliquids and liquidsolutions

Yes (Du Nouy pendantdrop Wilhelmy platecapillary rise)

Yes (parachor solubilityparameterscorresponding states)

Wetting adhesionlubrication

Interfacial tension ofliquidndashliquidinterfaces

Yes (Du Nouy) Yes (many methods egFowkes HansenGirifalcondashGood)

Surfactants

Surface tension of solids Yes (Zisman plotextrapolation fromliquid data solubilityparameters parachor)

Wetting and adhesion

Interfacial tension ofsolidndashliquid andsolidndashsolid interfaces

Yes (many methods egFowkes Hansen vanOssndashGood)

Wetting adhesioncharacterization andmodification ofsurfaceshellip (paintsglueshellip)

Contact angle betweenliquid and solid

Yes (many goniometersand other methods)

Yes (combination of Youngequation with a theoryfor solidndashliquidinterfaces)

Wetting adhesioncharacterization andmodification ofsurfaceshellip

Critical micelleconcentration ofsurfactants

Yes (change of surfacetension or otherproperties withconcentration)

Detergency

Surface or zeta potentialof particles

Yes (micro-electrophoresis)

Stability of colloidaldispersions

Adsorption of gasesliquids on solids

Yes (many methods) Yes (many theories egLangmuir BrunauerndashEmmettndashTeller (BET)Freudlich)

Stability surface analysis

Topography of a surface Yes (AFM STM) Surface analysis andmodification

HLB (hydrophilicndashlipophilic balance)

Yes (group contributionmethods solubilityparameters)

Design of emulsionsincluding stability ofemulsions anddetermining theemulsion type

Work of adhesion Yes (JKR AFM) Yes (the ideal one is viaYoungndashDupre andsimilar equations)

Adhesion detergency

8 Introduction to Applied Colloid and Surface Chemistry