ADSORPTION-INDUCED AGGREGATION OF COLLOIDAL PARTICLES IN BINARY-MIXTURES - MODELING THE PAIR FREE-ENERGY

Reversible aggregation of charged colloids in binary mixtures was firs t observed in 1985 by changing the temperature of the suspension. An a dsorbed layer was found to form around the colloids with increasing te mperature. Most of the tentative explanations have focused on either p hase transitions or surface transitions, such as the prewetting transi tion or capillary condensation. A simpler hypothesis is that the count er ions in the adsorbed layer progressively screen the surface charge as the temperature is increased toward the aggregation temperature. We model the pair free energy for this situation by examining the influe nce of an adsorbed layer on the repulsive potential and by using the D zyaloshinskii, Lifshitz, and Pitaevskii theory to represent the attrac tive dispersion interactions. (C) 1998 Academic Press.