Electric double layer for spherical particles in salt-free concentrated suspensions including ion size effects

TL;DR

This paper models the electric double layer around charged particles in salt-free suspensions, incorporating ion size effects to improve predictions of electrostatic phenomena like charge reversal.

Contribution

It introduces a numerical model that includes finite ion size effects in the electric double layer for concentrated salt-free suspensions, enhancing classical Poisson-Boltzmann approaches.

Findings

Finite ion size significantly affects potential and ion distribution profiles.

Corrections are crucial for high particle charges and concentrations.

Ion size considerations are essential for developing advanced theoretical models.

Abstract

The equilibrium electric double layer (EDL) that surrounds the colloidal particles is determinant for the response of a suspension under a variety of static or alternating external fields. An ideal salt-free suspension is composed by the charged colloidal particles and the ionic countercharge released by the charging mechanism. The existing macroscopic theoretical models can be improved by incorporating different ionic effects usually neglected in previous mean-field approaches, which are based on the Poisson-Boltzmann equation (PB). The influence of the finite size of the ions seems to be quite promising because it has been shown to predict phenomena like charge reversal, which has been out of the scope of classical PB approximations. In this work we numerically obtain the surface electric potential and the counterions concentration profiles around a charged particle in a concentrated salt-free suspension corrected by the finite size of the counterions. The results show the large importance of such corrections for moderate to high particle charges at every particle volume fraction, specially, when a region of closest approach of the counterions to the particle surface is considered. We conclude that finite ion size considerations are obeyed for the development of new theoretical models to study nonequilibrium properties in concentrated colloidal suspensions, particularly the salt-free ones with small and highly charged particles.