MICROSCOPIC THEORETICAL DESCRIPTION OF PHASE-STABILITY IN HARD-SPHERE YUKAWA MIXTURES

Phase stability properties of fluid mixtures composed of hard sphere particles interacting via an attractive Yukawa tail are studied in the mean spherical approximation. The theory shows how the occurrence of either liquid-liquid or liquid-vapour spinodal decomposition correlates with the interparticle potential parameters and the density rho* of the system. It appears that consolute-type decomposition is favoured at high rho* or when the 'unlike' to 'like' interaction strength ratio v is small; by contrast, liquid-vapour type decomposition takes place at low rho* or high nu values. A numerical estimate of the threshold density separating the two regimes of phase stability is made on the basis of a very simple modelling of the interaction energies. An analysis is also made of the q --> 0 limit of the partial structure factors S(ij)(q), which gives an insight into the modifications occurring in the microscopic structural arrangement of the system at the 'crossover' point. Possible applications to real fluid mixtures are discussed.