Equilibrium properties of a model electrolyte adsorbed in quenched disordered charged media: the ROZ theory and GCMC simulations

We present a theoretical study of the quenched-annealed system consisting o f an annealed +1: -1 electrolyte and a disordered quenched matrix modeled a s a charge and size asymmetric +Z: -1 electrolyte, with Z = 4 or 10. The an nealed electrolyte is in thermodynamic equilibrium with an external reservo ir of electrolyte at concentration C-b such that the chemical potentials of the confined and external electrolytes are equal. Both the matrix and the adsorbed electrolyte are modeled as charged hard spheres in a dielectric co ntinuum. The replica Ornstein-Zernike (ROZ) equations, supplemented by the hypernetted chain (HNC) approximation, are solved for this system. The effe cts of charge and size asymmetry of the matrix ions, their concentration, t he prequenched conditions on the pair distribution functions, and the therm odynamic properties of the annealed electrolyte are investigated. The conce ntration of adsorbed electrolyte cl is calculated as a function of the conc entration of external electrolyte c(b). For low concentration of external e lectrolyte, the average concentrations of electrolyte inside the matrix cl is higher than cb. On the contrary, for higher values of cb, the electrolyt e is desorbed from the matrix, c(l) < c(b). The theoretical results are sup plemented by data from a grand canonical Monte Carlo computer simulation. I t is shown that the ROZ/HNC theory yields results which are generally in go od agreement with the simulations.