FROM MIXING-DEMIXING TO CONDENSATION-EVAPORATION PHASE-TRANSITION IN BINARY LIQUIDS

Binary-fluid mixtures show first-order phase transition phenomena whic h are either classified as mixing-demixing (phase separation), or as c ondensation-evaporation. The localization of the transition lines, the characterization of the new phases, and the analysis of the parameter s which force model systems to choose one of the two transition mechan isms is the aim of this study. We performed both parallel-molecular-dy namics simulations and integral-equation theory calculations on binary mixtures of Lennard-Jones particles. By fixing the composition and by varying the interaction strength, we found a continuous change betwee n the two kinds of transition mechanisms. Theoretical and simulation r esults are compared with each other and a quantitative agreement is fo und. However, the simulation analysis appears to be more promising sin ce, in contrast to the integral-equation theory in which the spinodal lines can only be approched, information on the microscopic structure of the new phases can be obtained.