Charge neutrality breakdown in confined aqueous electrolytes: theory and simulation

TL;DR

This paper combines theoretical and simulation approaches to demonstrate that confined aqueous electrolytes between charged surfaces violate local charge neutrality, with implications for understanding electrostatic interactions in such systems.

Contribution

It introduces a Density Functional Theory based on bulk-HNC expansion that accurately models charge neutrality breakdown and electrostatic correlations in confined electrolytes.

Findings

Confined electrolytes lack local charge neutrality, consistent with recent experiments.

The DFT accurately predicts ionic density profiles and interaction forces.

Charge neutrality violation depends on plate separation and electrolyte concentration.

Abstract

We study, using Density Functional theory and Monte Carlo simulations, aqueous electrolyte solutions between charged infinite planar surfaces, in a contact with a bulk salt reservoir. In agreement with recent experimental observations [Z. Luo et al., Nat. Comm. 6, 6358 (2015)], we find that the confined electrolyte lacks local charge neutrality. We show that a Density Functional Theory (DFT) based on a bulk- HNC expansion properly accounts for strong electrostatic correlations and allows us to accurately calculate the ionic density profiles between the charged surfaces, even for electrolytes containing trivalent counterions. The DFT allows us to explore the degree of local charge neutrality violation, as a function of plate separation and bulk electrolyte concentration, and to accurately calculate the interaction force between the charged surfaces.