Micro and macrophase separation in discrete potential fluids]{Micro and macrophase separation in discrete potential fluids

We study the liquid-vapor phase diagram and the structural properties of discrete potential fluids by means of Gibbs ensemble simulations and integral equations theory. We consider three discrete fluids, namely, the square well (SW), the square well-barrier (SWB), and the square well-barrier-well (SWBW). They represent simple models for fluids with competing interactions that may exhibit a rich micro and macroscopic phase behavior depending on both strength and range of the attractions and repulsions in the potential. Here we emphasize the structural behavior near the liquid-vapor coexistence. Our findings indicate that for the SWB fluid a possible scenario of a microscopic phase separation, associated to a cluster-like formation near the critical region, is observed and could be understood as a frustration mechanism of the liquid-vapor transition when either the strength or the range of the repulsion increases. This microscopic-like separation can be inhibited by suppressing the repulsion or adding an additional well to the interaction potential. However, in the SW fluid of long-range potential, we have found results that point out towards evidence of a microscopic aggregation driven purely by attractions.