Phase separation in fluid additive hard sphere mixtures?

Abstract

Some years ago, Lebowitz and Rowlinson ‘established’ that phase separation did not occur in fluid mixtures of additive hard spheres. Their analysis was based on the thermodynamic functions of this mixture, obtained from the solution of the Percus-Yevick (PY) equation. At the time, these results were thought to be accurate for all states for which additive hard sphere mixtures were fluid. Recent theoretical work and simulations have shown that the PY radial distribution function between a pair of large spheres is seriously in error when the ratio of the diameters of the large and small spheres becomes large and when the concentration of the large spheres is very small. Thus, a reexamination of the question of phase stability in fluid additive hard sphere mixtures is worthwhile. Indeed, it is found that phase separation is probable in fluid additive hard sphere mixtures when the concentration of the large particles is very dilute. Generally, the coexisting phase is solid. However, under some circumstances, the coexisting phase may be fluid. This result may provide insight into the recently observed phase separation in colloids.