Introduction into the world of colloids

Joachim Koetz, Universität Potsdam

History of Colloid Chemistry

• Alchemy

Alchemist

• Elexier of life ?

• drinking gold-solution (aurum potabile)

HAuCl4

+ 3

+ reducing agent

What you would expect is

elementary gold

• What you find is an opticallyclear, red solution !!

HAuCl4 Optically clear, red solution

+ 3

History of Colloid Chemistry

1857 Faraday: Light scatteringstudies of colloidal gold sols

What is the reason for the red

colour ?

• If the particle dimensions are well defined a part of the visible light (bluelight) will be absorbed (surface plasmonresonance) and the colour of the solutionbecomes red !

History of Colloid Chemistry

• 1871 Rayleigh: Theory of light scattering

History of Colloid Chemistry

• 1861 Graham: Diffusion behaviour

Definition (Graham)

• Colloids are glue-like substances,

diffuse very slowly,

and do not dialyse

What is a Colloid ?

DEFINITION:

κολλα = glue

Thomas Graham

History of Colloid Chemistry

• 1907 Wolfgang Ostwald: Different typesof colloidal systems

DIE WELT DER VERNACHLÄSSIGTEN

DIMENSIONEN(The world of neglected dimensions)

EINE EINFÜHRUNG IN DIE KOLLOIDCHEMIE

MIT BESONDERER BERÜCKSICHTIGUNG

IHRER ANWENDUNGEN

VON

WOLFGANG OSTWALDPROF. DER KOLLOIDCHEMIE a. d. UNIVERSITÄT LEIPZIG

1927

suspensions> 1000 nm

Types of disperse systems (W. Ostwald)

Disperse systems

colloidal dispersions1 bis 1000 nm

solutions< 1 nm

Definition

Any particle that has some linear dimension between 1 nm and

1 µm is considered a colloid!

However, the limits are rather arbitrary.

• A state of subdivision in which the particles, droplets, or bubblesdispersed in anotherphase have at least onedimension between

1 – 1000 nm

• All combinations arepossible between gas, liquid, and solid

W. Ostwald

Definition:

Colloidal Systems(according to Wolfgang Ostwald)

Colloidal systemParticleMedium

Solid SuspensionSolidSolid

Porous MaterialLiquidSolid

Solid FoamGasSolid

SuspensionSolidLiquid

EmulsionLiquidLiquid

FoamGasLiquid

AerosolSolidGas

AerosolLiquidGas

History of Colloid Chemistry

• 1927 Burry, Ekwall: AssociatingColloids

Associating Colloids

• Amphiphilic self-organizing systems

• Colloids are associated physically, not chemically

• Size and shape of the associates canchange

History of Colloid Chemistry

• 1929 Staudinger: Macromolecules

Macromolecules as colloidalsystems

• Any macromolecule consisting of

103 up to 109 atoms

• Any dispersed macromolecular coilhaving colloidal dimensions

History of Colloid Chemistry

• 1923 Svedberg: Ultracentrifugation

• 1932 Ruska: First electron microscope

The Colloidal Domain

• One dimension between 1 and 1000 nm

• All combinations of dispersed matter

• Classification: - colloidal dispersions

- associating colloids

- macromolecules

Nanosized particles or macromolecules

Atom →→→→

Log (size in Meter)

20

18

16

14

12

10

8

6

4

2

0

-2

-4

-6

-8

-10

-12

-14

-16

Molecule →→→→

Electron →→→→

Macro

co

sm

os

Mic

roco

sm

os

←←←← Flea

←←←← Virus

←←←← Mouse

←←←← Bacterium

Life Science

←←←← Whale

←←←← Human

Sun →→→→

Earth →→→→

TV tower →→→→

brick →→→→

House →→→→

Hair →→→→

Colloidal region

MatterialScience

UltraUltra--high Resolution high Resolution ScanningScanning ElectronElectron Microscope Microscope

SS-- 4800 4800 (Hitachi)(Hitachi)SpecificationsSpecifications::

��Image Image resolutionresolution:: 1.0 nm / 15 kV1.4 nm / 1 kV

��EDXEDX-- SystemSystem::Thermo - NORAN system SIX

��CryoCryo preparationpreparation systemsystem: : Gatan – Alto 2500-S

��STEM STEM ImagingImaging

REM deutsch

Colloidal systems in Nature

Biomineralization

Bone and teethcomposite of collagenfilament

and protein

Hydroxylapatit, Ca10(PO4)6(OH)2

Pearlcomposite of hydrocarbon

and protein

Aragonite, CaCO3

Diatomeencomposite of hydrocarbon

and protein

SiO2 * x H2O

OrganismOrganiccomponent

Inorganiccomponent

• A state of subdivision in which the particles, droplets, or bubblesdispersed in anotherphase have at least onedimension between 1 and 1000 nm

• all combinations arepossible between :

gas, liquid, and solid

W. Ostwald

Colloidal systems

Fields of Application for nanostructured systems

Disciplines and Topics for which Colloids and colloidal phenomena are important

• Analytical chemistry

• Physical chemistry

• Biochemistry

• Material Science

• Petroleum Science

• Household products

• Imaging technology

• Adsorption phenomena, chromatography

• Nucleation, supersaturation, liquid crystals

• Electrophoresis, osmosis, ultrafiltration

• Ceramics, fibres, powder metallurgy• Oil recovery, • Milk, beer, cosmetics• Emulsions, printing inks, paper

coating

Colloids and Surfaces

• Special features of colloidalsystems

Surface area of colloidal systems

• Cube (1cm; 1cm; 1cm)after size reduction to an edge length of 500 nm:

���� surface area of 60 m2

• Spinning dope (1 cm3) after spinning to a fibre with diameter of 1000 nm:

���� fiber length of 1273 km

• 1 liter of a 0.1 M surfactant solution:���� interfacial area of 40000 m2

Colloidal systems

• have very large surface areas

Surface atoms [in %] in dependence on the particle size [in nm]

0102030405060708090

100

20 10 5 2 1

part of surfaceatoms in %

%

nm

Colloidal systems

• surface atoms become dominant

Surface tension

Increase in Gibbs free energy

per unit increment in area

Surface Tension Phenomena

• Droplet formation

• Coalescence

• Bubble formation

• Wetting

Marangoni-Effect

Processes induced by a change of surface tension

„Wine Tears“

• Alcohol is evaporatedfrom the liquid film at the glass wall

• Surface tension isincreased

• Wine is absorbed at the glass wall

• Droplets are flowingback into the glas