Entropy-driven phase transition in binary mixtures - art. no. 011402

Based on the principle of entropy maximum, a transparent method to study th e phase separation is proposed. The excluded volume effects of binary mixtu res of hard spheres with two different diameters an analyzed and the role o f entropy is emphasized. As a result of the entropy variation caused by the packing of large spheres, there is a critical volume fraction to denote th e phase boundary. it is shown that the variation of free volume fraction is influenced by the ratio a=d(L)/d(S) of large to small sphere diameters and the ratio x = eta (L)(eta (L) +n(S)) of large-sphere volume fraction to th e total volume fraction of large- and small-spheres. We introduce a modific ation factor beta to describe the overlap degree of two large spheres exclu ded volumes when they pack together. The critical volume fractions for larg e-sphere packing with different values of alpha and x are calculated, and t he corresponding phase boundaries are determined. Our results are in quite good agreement with previous experimental measurements.