Structure of fully asymmetric mixed electrolytes around a charged nanoparticle: a density functional and simulation investigation

Abstract

A systematic study on the structure of mixed electrolytes with arbitrary size and charge asymmetry around a charged nanoparticle is carried out using density functional theory and Monte Carlo simulation. A primitive model representation, with the spherical macroion surrounded by small ions in a continuum dielectric as the solvent, is used. A weighted density approximation is used to evaluate the hard-sphere correlation, whereas the ionic part is calculated using perturbation expansion around the bulk density. A canonical ensemble Monte Carlo simulation on the same system is also performed for comparison. Parametric variations on component ratios of the electrolyte, ionic concentrations, surface charge densities and macroion as well as small ion sizes show interesting phenomena of overcharging and charge reversal. The theoretical predictions are found to be in good agreement with the simulation results concerning the density as well as mean electrostatic potential profiles. The present study shows distinctive evidence of size and charge correlations around the interface, in a fully asymmetric situation.