Molecular solvent model of cylindrical electric double layers: A systematic study by Monte Carlo simulations and density functional theory

Abstract

We present the Monte Carlo simulation and density functional study of structure of cylindrical double layers considering solvent as the third component. We have chosen molecular solvent model, where ions and solvent molecules are considered as charged and neutral hard spheres, respectively, having equal diameter. The polyionic cylinder is modeled as an infinite, rigid, and impenetrable charged hard cylinder surrounded by the electrolyte and the solvent spheres. The theory is partially perturbative where the hard-sphere interactions are treated within the weighted density approach, the corresponding ionic interactions have been evaluated through second-order functional Taylor expansion with respect to the bulk electrolyte. The Monte Carlo simulations have been performed in canonical ensemble. The system is studied at varying concentrations of electrolyte ions and the solvent molecules, at different valences of the electrolyte, at different sizes of hard spheres, and at varying surface charge density. The theory and the simulation results are found to be in good agreement at different parametric conditions. The hard-sphere exclusion effects due to molecular nature of the solvent are shown to have special implications in characterizing diffuse layer phenomena such as layering and charge inversion.