ADSORPTION-INDUCED REVERSIBLE COLLOIDAL AGGREGATION

Reversible colloidal aggregation in binary liquid mixtures has been st udied for a number of years. As the phase separation temperature of th e liquid mixture is approached the thickness of an adsorption layer ar ound the colloidal particles increases. Beysens et al. [Phys. Rev. Let t. 54, 2123 (1985): Per. Bunsenges. Phys. Chem. 98, 382 (1994)] have d emonstrated experimentally that this adsorption layer is intimately co nnected with the aggregation of the colloidal particles; however, no d efinitive theory has been available that can explain all of the experi mental observations. In a recent work [J.-M. Petit, B. M. Law, and D. Beysens, J, Colloid Interface Sci. (to be published)] we have extended and improved the Derjaguin-Landau-Verwey-Overbeek theory of colloidal aggregation [E. J. W. Verwey and J. Th. G. Overbeek, Theory of the St ability of Lyophobic Colloids (Elsevier, New York, 1948)] by taking in to account the presence of an adsorption layer and by more realistical ly modeling the attractive dispersion interactions using the Dzyaloshi nskii-Lifshitz-Pitaevskii theory [Adv. Phys. 10, 165 (1961)]. In the p resent paper we apply this theory to a lutidine-water mixture containi ng a small volume fraction of silica colloidal particles. We demonstra te that the theory can quantitatively account for many of the experime ntally observed features such as the characteristics of the aggregated state, the general shape of the aggregation line, and the temperature dependence of the second virial coefficient.