Phase transitions in sterically stabilized silica colloids studied by adiabatic calorimetry

Adiabatic calorimetry measurements were made on colloidal silica particles (designated SJ4) coated with a dense layer of octadecyl chains. A dry powder consisting of these particles shows a phase transition at 284 K. This is attributed to an order–disorder transition in the stabilizing chains. Dispersing the particles in toluene shifts this order–disorder transition to lower temperatures. We propose a model in which the organic layer dissolves in the solvent at high temperatures and solidifies at low temperatures. This eutectic model predicts qualitatively correct the phase behavior of such colloidal dispersions. Particularly the pressure dependence of the phase transition is consistent with the model.