Electrostatic Stabilisation of Disperse Systems

Such a repulsive energy can be produced by charge separation and the creation of electrical double layers, as discussed in detail in Chapters 6 and 7. Combination of the van der Waals attraction and double layer repulsion at various separation distances between the particles produce an energy-distance curve, which will have an energy barrier at intermediate separations [10] and this is the origin of electrostatic stabilisation. The energy-distance curve is controlled by the following parameters. 

Equation (13.8) gives the van der Waals attractive energy, Ga, for two particles or droplets with equal radius R, and surface-to-surface separation h (when h R), 

The Hamaker constant of any material depends on the number of atoms per unit volume q and the London dispersion constant p, 

Ga is seen to increase very sharply with decreasing h when the latter reaches small values. In the absence of repulsion between the particles or droplets, the latter will aggregate (flocculate) by simple diffusion through the medium. This leads to fast flocculation kinetics and the rate constant for the process ko has been calculated using the Smolulokowski equation, 

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