INTEGRAL-EQUATION DESCRIPTION OF PHASE-STABILITY IN SIMPLE AND CHARGED FLUID MIXTURES

Recent results concerning phase stability of simple and charged fluid mixtures are reported. The applied theoretical appraoches are the hypernetted-chain (HNC) approximation and the mean spherical approximation (MSA). The MSA predictions for the existence of critical points and spinodal turn out to be qualitatively correct in all cases investigated although the thermodynamic inconsistency of the theory forbids a quantitative estimate of the location of these features. The determination of the phase stability conditions is also performed in the more accurate HNC, through an extrapolation procedure of the available results for the q=0 limit of the concentration-concentration structure factor S cc(0). Such an extrapolation is necessary since, as also found by other authors, the algorithm of solution becomes unstable in a region of the parameter space which, at high densities, can be identified with the spinodal. The same procedure allows us to establish that the HNC exhibits a power law behaviour in the high-density limit. Some applications to model systems which mimic real mixtures, and the related comparison with the experimental results, are discussed throughout. © 1990 Società Italiana di Fisica.