The influence of short-range attractive and repulsive interactions on the phase behaviour of model colloidal suspensions

The phase behaviour of simple systems interacting via model pair potentials that include both a hard core and additional short-range interactions is predicted using a classical density-functional-perturbation theory. The combination of a narrow attractive square well and a repulsive square barrier, approximating interactions in charge-stabilized colloidal suspensions, gives rise to isostructural solid-solid transitions whose stability is enhanced relative to that of the square-well potential alone. The temperature dependence of rms particle displacements for these idealized systems is shown, from both theory and Monte Carlo simulation, to behave anomalously at densities for which neighbouring barriers overlap.