2 Colloidal systemsA state of subdivision in which the particles, droplets, or bubbles dispersed in another phase have at least one dimension between 1 and 1000 nmall combinations are possible between :gas, liquid, and solidW. Ostwald
3 Surface area of colloidal systems Cube (1cm; 1cm; 1cm)after size reduction to an edge length of 500 nm: surface area of 60 m2Spinning dope (1 cm3)after spinning to a fibre with diameter of nm: fiber length of 1273 km1 liter of a 0.1 M surfactant solution: interfacial area of m2
4 Surface atoms [in %] in dependence on the particle size [in nm]
5 Colloidal systems have large surface areas surface atoms become dominant
6 Colloid stability Colloidal gold: stabilized against coagulation ! Creme: stabilized against coagulation !Milk: stabilized against coagulation !
7 Particle – Particle interactions dInteraction Energy ( Vtot) – Distance of Separation (d) Relationship
8 Vtot(d) = Vattr(d) + Vrep(d) - Van der Waals attraction Electrostatic repulsion- Steric repulsion
9 DLVO - Theory 1940 – Derjaguin; Landau; Verwey; Overbeek Long range attractive van der Waals forcesLong range repulsive electrostatic forces
10 DLVO – Theory Van der Waals attractive energy a) between two plates:b) between two spheres:
12 Gouy Chapman modelplanar double layerIons as point charges
13 I distribution of ions in the diffuse double layer Electrolyte theoryI distribution of ions in the diffuse double layer(Boltzmann equation)II equation for the room charge densityIII Poisson relationAus I, II und III folgt:Poisson – Boltzmann - relation
14 Solution of the P-B equation ()xekdy-×=2For small potentials (< 25 mV) :Integrable form
15 DLVO – Theory Electrostatic repulsive energy Resulting repulsive overlap energyBetween two plates:c° – volume concentration of thez – valent electrolyteb) Between two spheres
16 Vtot(d) = Vattr(d) + Vrep(d) Vvan der Waals = - A a / 12 d Velectrost. = k e-dA – Hamaker constanta – particle radiusd – distance between the particles1/ - thickness of the double-layer
17 Electrostatic stabilization stabilized against coagulation Kinetically stable stateenergetic metastable state in thesecondary minimumwith an energy barrier
18 Critical coagulation concentration (CCC) The energy barrier disappears by adding a critical amount of low molecular salts
19 DLVO – Theory (CCC)Vtot / dd = Vtot = 0 for two spheres:
20 DLVO – Theory (CCC)For two spheres the ccc should be related to the valency (1 : 2 : 3) of the counterions as:1000 : 16 : 1,3
21 CCC of a colloidal dispersion as a function of the salt concentration electrolyteCCC of aArsensulfid -DispersionSchulze-Hardy-ratioNaCl5,1 10-21000KCl5,0 10-21000MgCl27,2 10-413CaCl26,5 10-413AlCl39,3 10-51,7
22 Steric stabilizationWhat will be happen when we add polymers to a colloidal dispersion ?
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