Phase separation in dispersions of weakly-interacting particles in solutions of non-adsorbing polymer

Abstract

Phase separation may be induced in dispersions of hydrophobic silica particles in cyclohexane upon the addition of non-adsorbing polymer (polydimethylsiloxane). The origin of this effect is ascribed to the depletion interaction. Depending on the particle size and molecular weight of the polymer, the analogues of the molecular gas/solid, gas/liquid and liquid/solid co-existing phase regions may each be observed. It is demonstrated that using relatively simple, mean-field theories for both the fluid state (random phase approximation or adhesive sphere model), and also the solid state (cell model), all these transitions may be predicted. Although the quantitative agreement between experiment and theory is not exact, qualitatively all the observed trends in behaviour are accounted for.