Sources of Colloidal Stability

Knowing where the attractive interactions between colloidal particles stem from, we must now address the question of where the free energy maximum 

As the two particles approach, there will be two (at least) types of interaction the repulsive interaction just described and the relentless van der Waals attractive interactions, which make most colloids inherently unstable. The total interaction energy for the system under consideration will be the sum of the two energies 

A general expression for the repulsive interaction between the electrical double layers around two spherical particles is quite complex and does not warrant discussion here. A simple and relatively good approximate equation derived by Reerink and Overbeek is 

As pointed out in Chapter 5, the effective electrical potential of importance will be that at the Stern layer ij/s rather than that actually at the surface, if/o. 

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