Title: Colloid Stability ?
1Colloid Stability ?
2Colloidal systems
- A state of subdivision in which the particles,
droplets, or bubbles dispersed in another phase
have at least one dimension between 1 and 1000 nm
- all combinations are possible between
- gas, liquid, and solid
- W. Ostwald
3Surface 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
4Surface atoms in in dependence on the
particle size in nm
nm
5Colloidal systems
- have large surface areas
- surface atoms become dominant
6Colloid stability
- Colloidal gold stabilized against coagulation !
- Creme stabilized against coagulation !
- Milk stabilized against coagulation !
7Particle Particle interactions
d
- Interaction Energy ( Vtot) Distance of
Separation (d) Relationship
8Vtot(d) Vattr(d) Vrep(d)
- - Van der Waals attraction - Electrostatic
repulsion -
- Steric repulsion
9DLVO - Theory
- 1940 Derjaguin Landau Verwey Overbeek
- Long range attractive van der Waals forces
- Long range repulsive electrostatic forces
10DLVO TheoryVan der Waals attractive energy
11Double layer models
- Helmholtz
- Gouy Chapman
- Stern
12Gouy Chapman model
- planar double layer
- Ions as point charges
13Electrolyte theory
14Solution of the P-B equation
15DLVO TheoryElectrostatic repulsive energy
16Vtot(d) Vattr(d) Vrep(d)
- Vvan der Waals - A a / 12 d
Velectrost. k e-?d - A Hamaker constant
- a particle radius
- d distance between the particles
- 1/? - thickness of the double-layer
17Electrostatic stabilization
- stabilized against coagulation
- ? Kinetically stable state
- energetic metastable state in the
- secondary minimum
- with an energy barrier
18Critical coagulation concentration (CCC)
- The energy barrier disappears by adding a
critical amount of low molecular salts
19DLVO Theory (CCC)
20DLVO Theory (CCC)
- For two spheres the ccc should be related to the
valency (1 2 3) of the counterions as - 1000 16 1,3
21CCC of a colloidal dispersion as a function of
the salt concentration
electrolyte
Schulze-Hardy-ratio
CCC of a Arsensulfid -Dispersion
NaCl
1000
5,1 10-2
KCl
1000
5,0 10-2
MgCl2
13
7,2 10-4
CaCl2
13
6,5 10-4
AlCl3
1,7
9,3 10-5
22Steric stabilization
- What will be happen when we add polymers to a
colloidal dispersion ?
23Particle Particle interactions
Polymer adsorption layer
24Particle Particle interactions
Overlap of the polymer adsorption layer
25Overlap of the adsorption layer
- Osmotic repulsion
- Entropic repulsion
- Enthalpic repulsion
26Sterically stabilized systems can be controlled
by
- The thickness of the adsorption layer
- The density of the adsorption layer
- The temperature
27Stabilization and destabilization in dependence
on the molecular weight of the added polymer
28Stabilization and destabilization in dependence
on the polymer-concentration