Phase Behaviour of Hard-Sphere Mixtures

A recent method for treating colloid-polymer mixtures is extended to study the phase behaviour of hard-sphere mixtures. It is shown that, for small size ratios ξ r2/r1, the addition of small spheres (radius r2) to a system of large spheres (radius r1) induces bulk phase separation into coexisting crystal and fluid phases. Moreover, prior to inducing bulk crystallization, the small spheres cause crystallization of the large spheres next to a hard wall. The positions of the wall and bulk crystallization phase boundaries calculated for a size ratio of 0.14 compare favourably with a set of recent experimental results.