Sterically stabilized colloidal dispersions: beyond hard spheres

Sterically stabilized colloidal dispersions, such as PMMA, have long been r egarded as archetypal realizations of hard spheres and hard-sphere mixtures . Indeed, this is precisely what is found in studies of these systems as a function of the volume fraction, at constant temperature. However, a much r icher behaviour-which goes beyond what is expected from just hard spheres-i s found as a function of both volume fraction and temperature T. For instan ce, sterically stabilized colloids are known to exhibit both upper (high-T) and lower (low-T) two-phase behaviour, such that the former is temperature sensitive but the latter is not. We review model calculations based on a double Yukawa potential that exhibi ts some of the rich phase behaviour found experimentally, and predicting ot her behaviour which has not yet been found by experiment. Both the former a nd latter show a degree of similarity to the phase behaviour of polymer sol utions. We also present preliminary results for the phase behaviour of bidi sperse model sterically stabilized colloids.