Description of concentration fluctuations in liquid binary mixtures with nonadditive potentials

The segregation or phase separation in a binary mixture is investigated within a quasilattice model and the hard-sphere-like model. The hard-sphere results are improved by incorporating a nonadditive attractive tail interaction. An analytic expression for the concentration fluctuation Scc(0) is obtained for the Lennard-Jones system and its equivalence to the lattice-based model is established. The results suggest that the segregation or phase separation, with either model, is an outcome of the energetic effect.