Effect of solvent polarization on electric double layer of a charged soft surface in an electrolyte solution

TL;DR

This study investigates how solvent polarization influences the electric double layer near a charged soft surface in an electrolyte, revealing significant effects on electrostatic potential, ion densities, and permittivity through a mean-field model.

Contribution

It introduces a mean-field approach that incorporates solvent polarization and non-uniform ion sizes to analyze the electric double layer near charged soft surfaces.

Findings

Solvent polarization significantly affects electrostatic potential and ion densities.

Considering solvent polarization increases the magnitude of the Donnan potential.

Water permittivity and dipole density decrease with high surface charge density.

Abstract

We study the electric double layer near a charged soft surface by using a mean-field approach including non-uniform size effect and solvent polarization. Based on a free energy model, electrostatic potential and number densities of water and ions are obtained numerically by solving coupled differential equations including the Poisson's equation. We find that the solvent polarization significantly affects electrostatic potential, ion number densities and permittivity in an electrolyte solution near a charged soft surface. We prove that the consideration of the solvent polarization increases the magnitude of Donnan potential. We also demonstrate that within the fixed charge layer the number densities of counterions and coions are slightly smaller than when the solvent polarization is not considered. An increase in the ionic size enhances the influence of solvent polarization on the electrostatic properties within the fixed charged layer of charged soft surface. In the region of high surface-charge-density, the permittivity and the number density of water dipoles considerably decrease due to water polarization.