Modelling Electrolyte Adsorption in Nanoporous Materials

The structural and thermodynamic properties of a model electrolyte solution confined in disordered matrices with charged obstacles were studied by means of the grand canonical Monte Carlo simulation. A disordered nanoporous medium was modelled as i) an equilibrium distribution of ions in a +1:-1 primitive model electrolyte; ii) a system of dipolar hard spheres; iii) a collection of chainlike molecules with alternating charge on the beads (polyampholyte); and iv) as a system of charged chainlike molecules (oligoelectrolyte) with the pertaining counterions. The confined electrolyte was assumed to be in thermodynamic equilibrium with the obstacles forming the nanoporous matrix and an external electrolyte of the same chemical composition. The solvent in all these cases was treated as a dielectric continuum. In the present study we were interested in effects of the distribution of charged obstacles on the mean activity coefficient of the confined electrolyte. The computer simulations were performed for a set of values of the model parameters such as the concentration of matrix ions and of the annealed electrolyte, pre-quenching conditions and the conditions of observation. The results confirmed our previous findings that the properties of an annealed electrolyte depend strongly on the conditions of observation (temperature and dielectric constant of solvent), as well as on the concentrations of all components. The effect of the matrix-charge distribution, investigated in this work, was found to be significant and more important for higher Coulomb couplings.