Microphase and macrophase separations in discrete potential fluids

Abstract

In this paper, we studied the liquid-vapor phase diagram and structural properties of discrete potential fluids using Gibbs ensemble simulations and integral equations theory. For this, we considered three discrete fluids, namely, the square well, square well-barrier, and square well-barrier-well. They represent simple models for fluids with competing interactions that exhibit a rich microscopic and macroscopic phase behavior depending on both the strength and range of the attractions and repulsions in the potential. Here, we emphasized a structural behavior near the liquid- vapor coexistence. For the square well-barrier fluid, we observed a possible scenario of a microscopic phase separation associated with a cluster-like formation near the critical region, which could be interpreted as a frustration mechanism of the liquid-vapor transition when either the strength or range of repulsion increases. This microscopic- like separation can be inhibited by suppressing the repulsion or adding an extra well to the interaction potential. However, for the square well fluid with long-range potential, we found evidence of a microscopic aggregation driven solely by attractions.