Estudo do Comportamento de Fase do Modelo Primitivo Restrito para Eletrólitos Simples Confinados num Meio Poroso

Abstract

The study of thermodynamic properties of complex fluids confined in a porous media is a problem of fundamental importance in many scientific fields. New nanomaterials with large applications in biomedical devices, sensor and computing technologies are examples were the experimental setup was able to build new materials with controlled porosity. From a theoretical and computational point of view, most of the studies related to the equilibrium properties in this field have used short-range forces as the driven interactions, such as Lennard-Jones particles. The phase diagrams that have emerged from these studies present a very rich behavior, with new fluid-fluid separations and critical points, not observed in bulk conditions. In contrast, the study of charged systems, such as simple electrolytes under confinement in a porous media, is far from complete and no completely reliable approach has emerged yet. In this work Monte Carlo simulations in the grand-canonical ensemble have been performed to study the phase behavior of simple electrolyte confined in a porous media. Multihistogram reweighting and mixed-field finite-size scaling methods were used to obtain the phase diagrams and critical parameters of the restricted primitive model (RPM) of ionic fluids as a function of the porosity of the matrix inside which the electrolyte is immersed. We are particularly interested in obtaining the behavior of the RPM phase envelope when the porosity is modified, starting from the bulk (no porous matrix) to the limit where the matrix particles are very dense. Our results show that the critical temperature and density decrease with decreasing matrix porosity due to the confinement, specially the temperature. This gas-liquid critical point belongs to the 3 dimensional Ising universality class. We also find a second fluid-fluid phase separation in the low porosity limit, which is not found for the Coulomb gas in bulk conditions, only for the uncharged Lennard-Jones fluids confined in a porous media.