A MODEL FOR THE FREEZING OF BINARY COLLOIDAL HARD-SPHERES

Phase boundaries are calculated for the freezing of a binary mixture of colloidal hard spheres which are assumed to be immiscible in a single solid phase. Results are reported for mixtures of diameter ratio gamma =0.85 and 0.65. It is shown that the fluid phase is stable to a higher density in the binary mixture than the monodisperse system. The maximum fluid freezing density occurs at the binary eutectic in suspensions rich in small spheres. The proportion of small spheres in the eutectic fluid increases sharply with decreasing diameter ratio. At phase coexistence the hard sphere crystal is compressed relative to the monodisperse system. The increase in density is most pronounced for the crystal of large spheres. The hard sphere phase behaviour is described at constant volume which enables a direct comparison with experimental measurements on colloidal systems to be made.