Phase stability of dense charged hard sphere fluid mixtures

The mean spherical approximation (MSA), the hypernetted-chain (HNC) approximation, and Monte Carlo (MC) calculations are used in order to investigate the phase stability of dense charged hard sphere fluid mixtures. According to the MSA, spinodal decomposition occurs in these systems in a certain range of the physical parameters. The HNC results indicate the existence of a spinodal line in qualitative agreement with the MSA prediction. Local compositions obtained by MC calculations show the expected behavior in a mixture approaching segregation. The concentrations of the coexisting phases are also calculated within the MSA, and the characteristics of the phase diagrams of different types of mixture are discussed. A detailed analysis is then made of the thermodynamic quantities which define the Gibbs free energy of mixing; this allows one to understand in more detail the segregation process. Finally, the applicability of the present approach for studying the phase stability conditions of molten salt mixtures and ionic micellar solutions is discussed.