Generic transport coefficients of a confined electrolyte solution

TL;DR

This paper reconstructs electrokinetic transport parameters in confined electrolyte solutions using molecular dynamics simulations and Green-Kubo methods, revealing complex behaviors like flow reversal at high salt concentrations.

Contribution

It introduces a numerical scheme to evaluate transport coefficients from MD simulations, linking microscopic parameters to macroscopic electrokinetic phenomena.

Findings

Transport coefficients are successfully reconstructed from MD simulations.

Anomalous flow reversal occurs at high surface charge and salt concentrations.

The influence of salt concentration on electrokinetic transport is quantitatively analyzed.

Abstract

Physical parameters characterising electrokinetic transport in a confined electrolyte solution are reconstructed from the generic transport coefficients obtained within the classical non-equilibrium statistical thermodynamic framework. The electro-osmotic flow, the diffusio-osmotic flow, the osmotic current, as well as the pressure-driven Poiseuille-type flow, the electric conduction, and the ion diffusion, are described by this set of transport coefficients. The reconstruction is demonstrated for an aqueous NaCl solution between two parallel charged surfaces with a nanoscale gap, by using the molecular dynamic (MD) simulations. A Green-Kubo approach is employed to evaluate the transport coefficients in the linear-response regime, and the fluxes induced by the pressure, electric, and chemical potential fields are compared with the results of non-equilibrium MD simulations. Using this numerical scheme, the influence of the salt concentration on the transport coefficients is investigated. Anomalous reversal of diffusio-osmotic current, as well as that of electro-osmotic flow, is observed at high surface charge densities and high added-salt concentrations.