EXACT RESULTS FOR PHASE-SEPARATION IN AN ASYMMETRIC MODEL OF AN INTERACTING BINARY MIXTURE

We obtain exact coexistence curves for a two-dimensional lattice model of an asymmetric binary mixture of large and small molecules (squares and triangles, respectively), in which there is an energy cost epsilon for edge contact between a square and a triangle. For phase separation to occur, the coupling parameter e(-betaepsilon) must be smaller than a critical value. As epsilon varies, the model interpolates between the two hard-square systems formed when epsilon = 0 or epsilon = infinity. Phase separation occurs only for sufficiently large epsilon. A high packing density is also necessary to drive the demixing process.