Numerical study of freezing in polydisperse colloidal suspensions

We have established the solid-fluid coexistence region for a system of polydisperse hard spheres with near-Gaussian diameter distributions, as a function of polydispersity. Significantly, we observe a 'terminal' polydispersity above which there can be no fluid-solid coexistence. At the terminus the polydispersity is 5.7% for the solid and 11.8% for the fluid while the volume fractions are 0.588 and 0.547 for the solid and fluid respectively. Substantial fractionation observed at high values of the polydispersity (>5%) implies that the 'constrained eutectic' assumption made in previous theoretical studies is not generally valid. Our results for the terminal polydispersity are consistent with experiments performed on polydisperse colloidal suspensions.