Modeling of solvation interactions in non-polar dispersions of colloidal particles using the liquid state theory of adhesive hard sphere mixtures

Abstract

Colloidal particles dispersed in a non-polar solvent are modeled by a binary mixture of large spheres in a “solvent” of small spheres using the liquid state model of adhesive hard sphere mixtures. The discrete nature of the solvent molecules is explicitly taken into account. Solvation forces can be described fairly well using both solvent-solvent and solvent-solute interactions. By increasing the solvent-solvent interaction, keeping the solvent-solute interaction constant, the effective attraction between the large colloidal particles increases. The isothermal osmotic compressibility goes to infinity when the adhesive strength between the solvent molecules becomes very high and phase separation may occur (“poor” solvation). By increasing the solute-solvent interaction, keeping the solvent-solvent interaction constant, the effective repulsion between the large particles increases (“good” solvation). — When the solvent density is small (near the “critical” value), however, solvent-solute interactions may ultimagely lead again to effective attractions between the large spheres, if the adhesive strength between the solvent and solute particles is large enough. This phenomenon may be interpreted in terms of “bridge formation”.