PHASE-SEPARATION IN FLUID ADDITIVE HARD-SPHERE MIXTURES

Some years ago, Lebowitz and Rowlinson 'established' that phase separa tion did not occur in fluid mixtures of additive hard spheres. Their a nalysis was based on the thermodynamic functions of this mixture, obta ined from the solution of the Percus-Yevick (PY) equation. At the time , these results were thought to be accurate for all states for which a dditive hard sphere mixtures were fluid. Recent theoretical work and s imulations have shown that the PY radial distribution function between a pair of large spheres is seriously in error when the ratio of the d iameters of the large and small spheres becomes large and when the con centration of the large spheres is very small. Thus, a reexamination o f the question of phase stability in fluid additive hard sphere mixtur es is worthwhile. Indeed, it is found that phase separation is probabl e in fluid additive hard sphere mixtures when the concentration of the large particles is very dilute. Generally, the coexisting phase is so lid. However, under some circumstances, the coexisting phase may be fl uid. This result may provide insight into the recently observed phase separation in colloids.