Phase-Separation In Dispersions Of Weakly Interacting Particles Induced By Nonadsorbing Polymer

The addition of a non-adsorbing polymer (polydimethylsiloxane) to dispersions of hydrophobic silica particles in cyclohexane induces phase separation by means of the depletion interaction. The strength and range of the weak, attractive potential, in this otherwise hard sphere system, may be independently controlled by means of the free polymer concentration and molecular weight, respectively. Depending on the particle size and molecular weight of the polymer, as well as the particle number concentration, analogues of the molecular gas/liquid, gas/solid and liquid/solid phase transitions may each be observed, in accordance with the predictions of recent statistical mechanical theories. Key Words: Particulate phase separationweakly-interacting particlesdepletion flocculation