Modern Approaches to Wettability

Theory and Applications

Edited by

Malcolm E. Schrader Institute of Chemistry The Hebrew University of Jerusalem Jerusalem, Israel

and

George I. Loeb Geomar Associates Bethesda, Maryland

formerly of

David Taylor Research Center Ship Materials Engineering Department Annapolis, Maryland

Plenum Press • New York and London

Contents

Chapter 1 The Modern Theory of Contact Angles and the Hydrogen Bond Components of Surface Energies Robert J. Good and Carel J. van Oss

1. Introduction 1 2. Acid-Base Interactions and the New Surface Parameters 3 3. Contact Angles 7 4. Application of the Lewis Acid-Base Parameters to Contact Angles in

Practical Systems 11 5. Acidic and Basic Parameters of Selected Solid Surfaces 14 6. Discussion of the General Magnitudes of the y e and ye Parameters 16 7. Negative Interfacial Free Energy 18

7.1. Difference between Interfacial Tension and Interfacial Free Energy . . 18 7.2. Liquid-Solid Interfaces 19

8. An Apparent Anomaly That Arises from Certain Observed Contact Angle Data 20

9. Critique of Some Other Methodologies 22 9.1. Use of Liquid Mixtures 22 9.2. The "Equation of State" Interfacial Theory 22

10. A Note on Contact-Angle Measurement 23 10.1. Hysteresis 23 10.2. The Drop Size Effect 24 Acknowledgment 25 References 25

Chapter 2 The Long-Range Attraction between Macroscopic Hydrophobie Surfaces H. K. Christenson

1. Introduction , 29 1.1. Background 29 1.2. The Hydrophobie Effect between Nonpolar Solute Molecules 30 1.3. The Interfacial Energy between Water and Hydrocarbon 31 1.4. Cavitation 31

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2. Indirect Observations of the Hydrophobie Attraction 32 3. Direct Force Measurements 33

3.1. The Surface Force Apparatus 33 3.2. Preparation of Hydrophobie Surfaces 33 3.3. Interpretation of Direct Force Measurements 34

4. The Hydrophobie Attraction between Adsorbed Monolayers 35 4.1. Initial Experiments—CTAB Monolayers 35 4.2. Further Work on Adsorbed Monolayers 36 4.3. Cavitation between Adsorbed Surfactant Monolayers 37

5. The Hydrophobie Attraction between Deposited Monolayers 37 5.1. Weakly Charged Monolayers 37 5.2. Neutral Monolayers 39 5.3. Cavitation between Deposited Monolayers 42 5.4. The Electrolyte Dependence of the Hydrophobie Attraction 44

6. The Hydrophobie Attraction between Chemically Hydrophobed Surfaces.. 46 7. Theory 47 8. Remaining Problems and Future Research 48

References 50

Chapter 3 High- and Medium-Energy Surfaces: Ultrahigh Vacuum Approach Malcolm E. Schrader

1. Introduction 53 1.1. High- and Low-Energy Surfaces 53 1.2. Contamination 53 1.3. Theory of Interfacial Interaction 54

2. Metals 55 2.1. Theory of Interaction at the Water-Metal Interface 55 2.2. Gold 55 2.3. Ultrahigh Vacuum Method of Contact Angle Measurement: Water

on Gold 56 2.4. Ultrahigh Vacuum Contact Angle Measurements on Copper and

Silver 58 2.5. Surface Segregation 59 2.6. Surface Structure 60

2.7. Theoretical Interpretation of Experimental Results: Impact of New Hamaker Coefficient Calculations 60

2.8. Conclusions on Metal Wettability by Water 62 3. Glasses 62

3.1. Relative Humidity Experiments at Atmospheric Pressure 62 3.2. Experiments in Conventional Vacuum 63 3.3. Ultrahigh Vacuum Silanol-Siloxane 63 3.4. Discussion 65 3.5. Conclusions: Apparent Nature of Glass Surface Based on Vacuum

Experiments Alone 66 3.6. Contact Angles on Clay Minerals 66

CONTENTS XVII

4. Graphite: A Medium-Energy Surface 67 4.1. Introduction 67 4.2. Experimental Approach: UHV-AES-LEED 67 4.3. Results 68 4.4. Discussion 69

5. Conclusions 70 References 71

Chapter 4 Determination of the Surface Energy of Solids by the Two-Liquid-Phase Method Jacques Schultz and Michel Nardin

1. Introduction 73 2. Principle of the Two-Liquid-Phase Method 75

2.1. Principle of the Method 75 2.2. Wetting Criteria 76 2.3. Application of a Model Surface: Mica 77

3. Characterization of High-Energy Surfaces 79 3.1. Aluminum 79 3.2. Glass 81 3.3. Carbon 83 3.4. Fibers 84

4. Characterization of Low-Energy Surfaces 91 4.1. Orientation Phenomenon 92 4.2. Hysteresis Phenomenon 94

5. Conclusion 98 References 98

Chapter 5 The Equation of State Approach to Interfacial Tensions /. K. Spelt, D. Li, and A. W. Neumann

1. Introduction 101 2. Existence of an Equation of State 104

2.1. Interfacial Gibbs-Duhem Equations 104 2.2. Phase Rule for Interfacial Systems 105

3. Formulation of the Equation of State 108 3.1. Role of Adsorption 108 3.2. Equation of State—Original Formulation 110 3.3. Equation of State—Alternative Formulation 114

4. Experimental Support for the Equation of State 119 4.1. Direct Force Measurements 119 4.2. Solidification Front Experiments 120 4.3. Contact Angles for Different Liquids 123 4.4. Sedimentation Volumes 124

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4.5. Particle Suspension Layer Stability 128 4.6. Verification of the Equation of State Concept and Comparison with

the Surface Tension Component Approach 130 5. Alternative Equations of State 132

5.1. Sedimentation Volumes 133 5.2. Solidification Front Technique 134 5.3. Contact Angles 135

6. The Possibility of Negative Solid-Liquid Interfacial Tensions 136 7. Future Development of the Equation of State 139

Appendix 140 References 141

Chapter 6 Thermal Reconstruction of the Functionalized Interface of Polyethelene Carboxylic Acid and Its Derivatives Gregory S. Ferguson and George M. Whitesides

1. Introduction 143 1.1. Surfaces, Interfaces, and Interphases 144 1.2. Synthesis of Surface-Modified Polyethelene and Nomenclature Used

in Describing These Systems 145 1.3. The Role of Thermodynamics in Determining Interfacial Properties

and the Kinetics of Their Approach to Equilibrium 146 2. Wettability as a Probe of Surface Structure 147

2.1. Contact Angles: Definitions and Background 147 2.2. Reconstruction of the Surface of PE-C0 2H: Initial Observations 149 2.3. Model Systems for Studies of Wetting: Self-Assembled Monolayers

(SAMs) of Alkanethiols on Gold 150 2.4. Wetting Experiments on PE-X 154 2.5. Sensitivity of Wetting to Small Conformational Changes within the

9 Interphase 155 3. Reconstruction of the Interface of PE-C0 2H and Derivatives on

Heating 157 3.1. Comparison of Results from Wetting and XPS 157 3.2. Results from ATR-IR 158 3.3. Kinetic Model for Reconstruction of the Interface of PE-C0 2H 160 3.4. Reconstruction of the Interface of Derivatives of PE-C0 2H 164 3.5. Reconstruction of the Interface of PE-C0 2 H and Derivatives on

Heating in Contact with Liquids 166 3.6. Recovery of Polar Functional Groups from the Sub-Ö Interphase 169 3.7. Depth Profiling of PE-C0 2H and Derivatives during the Thermal

Reconstruction of Their Interfaces 169 3.8. Is Interfacial Strain a Driving Force for the Reconstruction of the

Surface of PE-C0 2 H? 171 4. Conclusions 172 5. Acknowledgments 175

References 175

CONTENTS xix

Chapter 7 Block Copolymers and Hydrophilicity Atsushi Takahara

1. Introduction 179 2. Characterization Methods of Polymer Hydrophilicity 180

2.1. Spreading Phenomena 180 2.2. Surface Characterization Techniques 182

3. Diblock and Triblock Copolymers 185 3.1. Polystyrene-Polydiene Diblock and Triblock Copolymers and Their

Derivatives 185 3.2. Polystyrene-Polytetrahydrofuran Diblock and Triblock Copolymers . . 187 3.3. Polystyrene-Polydimethylsiloxane Diblock and Triblock Copolymers 187 3.4. Polystyrene-Poly(ethylene oxide) Diblock Copolymer 188 3.5. Poly(hydroxyethyl methacrylate)-Polystyrene Triblock Copolymer . . . 188 3.6. Block Copolypeptides 189 3.7. A-B-C Triblock Copolymers 192

4. Charge Mosaic Membrane 193 5. Multiblock Copolymers 195

5.1. Segmented Polyurethanes 196 5.2. Other Multiblock Copolymers 202

6. Block Copolymers with Graft Side Chains 204 7. Conclusion 209

Acknowledgment 210 References 210

Chapter 8 Wettability and Bioadhesion in Ophthalmology Frank J. Holly

1. Introduction 213 2. Basic Considerations 214

2.1. Thin Aqueous Film Stability 214 2.2. Meniscus-Induced Local Thinning 216 2.3. Formation of Lipid Layers on Water 217 2.4. Water Wettability of Solid Surfaces 218 2.5. Hydrophilic-Hydrophobic Surface Transition 220

3. Applications to the Ocular System 222 3.1. Preocular Tear Film 222 3.2. Contact Lens Wear 229 3.3. Adhesion and Erosion of Corneal Epithelium 234 3.4. Retinal Adhesion and Its Failure 239 3.5. Wetting in Intraocular Surgery 242

4. Conclusions 245 References 246

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Chapter 9 Wettability of Surfaces in the Oral Cavity H. J. Busscher

1. The Importance of Surfaces in the Oral Cavity 249 2. Wettability of Oral Surfaces 250

2.1. Enamel and Dentine Surfaces 251 2.2. Oral Microbial and Mucosal Surfaces 252 2.3. Surfaces of Restorative Materials 253

3. Surface Free Energies of Oral Tissues 254 4. Oral Adhesion Phenomena and Surface Free Energies 256 5. Modifikation of the Physicochemical Properties of Tooth Surfaces 259 6. Concluding Remarks 259

Acknowledgments 259 References 260

Chapter 10 Wettability as a Surface Signal for Sessile Aquatic Organisms James W. Mihm and George Loeb

1. Introduction 263 2. Aquatic Organisms 263

2.1. Reversible Attachment 264 2.2. Permanent Attachment 264

3. Wettability 264 4. Microorganisms 265 5. Thermodynamic Interpretation 266 6. Macroscopic Attachment 269

6.1. Life Cycles and Metamorphosis 269 6.2. Barnacles and Musseis 269

7. Physical Forces versus Behavior 275 8. Summary 276

Acknowledgment 277 References 277

Chapter 11 Wettability of Clay Minerals Shmuel Yariv

1. Introduction 279 2. Structure of Clay Minerals 280

2.1. The Tetrahedral Sheet 280 2.2. The Octahedral Sheet 281 2.3. The TO-Type Layer Silicates 282 2.4. The TOT-Type Layer Silicates 283

CONTENTS xxi

3. Wettability of the Oxygen Plane 287 3.1. The dn-pn Bond 287 3.2. The Double Bond Character of the Si —O Bond of Siloxanes in Clay

Minerals 289 3.3. Wettability of Tale, Pyrophylhte, and Vermicuhte 290 3.4. The Extent of the Smectite-Water Interaction 291

4. Wettability of the Hydroxyl Plane 292 5. Wettability of Broken-Bond Surfaces 293

5.1. Dissociative Chemisorption of Water 296 5.2. Adsorption of Molecular Water 297 5.3. Hydration of Sepiolite and Palygorskite 300

6. Water in the Interlayer Space of TOT Minerals 301 6.1. Swelling 301 6.2. The Fine Structure of Interlayer Water 303 6.3. Acidic and Basic Properties of the Interlayer Space 312 6.4. Stages of Hydration of the Interlayer Space 316

7. Intercalated Water in Kaolinite 321 Acknowledgment 323 References 323

Chapter 12 Penetration and Displacement in Capillary Systems Abraham Marmur

1. Introduction 327 2. Equilibrium Conditions of Interfaces 329

2.1. The Contact Angle 329 2.2. The Pressure Difference across an Interface 333

3. Equilibrium in Capillary Systems 333 3.1. The Cylindrical Capillary 334 3.2. Equilibrium and Hysteresis in Porous Media 339

4. Kinetics of Penetration 348 4.1. The Cylindrical Capillary 348 4.2. Kinetics of Penetration into Porous Media 353

5. Concluding Remarks 355 References 356

Chapter 13 The Wetting Behavior of Fibers Willard D. Bascom

1. Introduction 359 2. Theory 359 3. Measurement Techniques 362

3.1. Goniometry 362

xxii CONTENTS

3.2. Drop Shape 362 3.3. Meniscus Shape 363 3.4. Flotation 363 3.5. Tensiometry (Wilhelmy Plate Method) 365

4. Experimental Observations 369 4.1. Static Contact Angles 369

5. Conclusions 371 Acknowledgment 372 References 372

Chapter 14 Wettability Phenomena and Coatings Clifford K. Schoff

1. Introduction 375 2. Consequences of Poor Wetting or Dewetting 376

2.1. Introduction 376 2.2. Substrates 376 2.3. Pigments 376

3. Substrate Wetting 377 3.1. Introduction 377 3.2. Wettability Tests 377 3.3. Dewetting Tests 383 3.4. Other Characterization Methods 384 3.5. Dynamic Surface Tension Effects 385 3.6. Viscosity Effects 385 3.7. Miscellaneous Effects 386 3.8. Techniques Used To Improve Substrate Wetting 387

4. Pigment Wetting 388 4.1. The Importance of Pigments 388 4.2. The Process of Pigment Dispersion 388 4.3. Wetting of the Pigment Powder 389 4.4. Pigment Wettability Testing 391 4.5. Improvement of Pigment Wetting 392

5. Conclusions 393 References 394

Chapter 15 Spreading on Liquids: Effect of Surface Tension Sinks on the Behavior of Stagnant Liquid Layers Eli Ruckenstein, D. G. Suciu, and O. Smigelschi

1. Introduction 397 2. Effect of Surface Tension Sinks on Stagnant Liquid Films 398

2.1. Experimental 398

CONTENTS xxiii

2.2. Results 399 2.3. Discussion 400

3. Study of the Pure Marangoni Effect 401 3.1. The Steady Dissolving Drop 402 3.2. Steady Heat Source 411

4. Mass Transfer Enhancement due to Surface Movements Produced by a Dissolving Liquid 414 4.1. Mass Transfer Measurements 414 4.2. Theory 414 4.3. Comparison between Experiment and Theory 415

5. Additional Experimental Observations 416 5.1. The Dissolving Film 416 5.2. Movements of the Free Surface 419 5.3. Movements within the Water Layer 421 Notation 421 References 422

Chapter 16 Nucleation on Smooth Surfaces Joseph L. Katz, Jin Sheng Sheu, and Jer Ru Maa

1. Introduction 423 2. Model 423 3. Relationship of the Variables 425 4. Homogeneous Nucleation 425 5. Growth of Clusters 429 6. Critical Supersaturation 430 7. Conclusions 432

Acknowledgment 432 Appendix 432 References 434

Index 435