Pressure-induced phase transition in sterically stabilized colloids

Increasing the pressure on stable dispersions of sterically stabilized silica particles in toluene induces a phase transition. This transition can also be induced by lowering the temperature. The dispersion separates into two phases with different particle densities. The origin of the phase behavior cannot be explained with the classical Flory-polymer-physics model. Here we attribute the observed behavior to a ‘‘local ordering’’ or ‘‘liquid-crystalline-like phase transition’’ of the stabilizing moieties grafted to the particles. Through such an effect we can consistently explain the observed phenomena and particularly the high value of the differential quotient dp/dTtrans =+77 bars/K for the phase transition temperature at which the dispersion separates into two liquid phases of different particle concentrations.