Solvent primitive model for electrolyte solutions in disordered porous matrices of charged species. Replica Ornstein-Zernike theory and grand canonical Monte Carlo simulations

Abstract

We present a theoretical study of a quenched–annealed system in which an annealed component is the restricted primitive model electrolyte in a mixture with an uncharged hard sphere species, i.e. the solvent primitive model (SPM), whereas a disordered quenched medium is modelled as the restricted primitive model (RPM) electrolyte. The annealed mixture is in thermal and chemical equilibrium with an external reservoir containing the same SPM. The system is studied by using the replica Ornstein–Zernike (ROZ) integral equation theory complemented with the hypernetted chain (HNC) approximation and via the grand canonical Monte Carlo simulations. We are primarily interested in collecting computer simulation data and comparing them with theoretical predictions at room temperature (298.15 K). In terms of physical observables, our focus is in the selectivity effects of adsorption of the mixture described by the adsorption isotherms as well as by the composition isotherms. The influence of the ionic matrix density and of the bulk state of the SPM mixture on adsorption and selectivity are examined in detail. Besides, we analyse the dependence of the internal energy and the constant volume heat capacity on the conditions of adsorption. Finally, we explore briefly the effects of quenching conditions of the RPM matrix on the pair distribution functions of fluid ions in the mixture. In general, the theory is in a very good agreement with computer simulations.