Charge transport in nanochannels: a molecular theory

TL;DR

This paper develops a self-consistent kinetic theory-based numerical method to study charge transport in nanochannels, capturing microscopic layering, flow properties, and effects of channel shape and roughness.

Contribution

It introduces a novel molecular theory and Lattice Boltzmann simulation approach for electrokinetic flow in nanoconfined channels, including complex geometries.

Findings

Layering effects near walls observed at molecular level

Flow profiles and charge transport quantified in various channel shapes

Significant deviations from electroneutrality at nanoscales

Abstract

We introduce a theoretical and numerical method to investigate the flow of charged fluid mixtures under extreme confinement. We model the electrolyte solution as a ternary mixture, comprising two ionic species of opposite charge and a third uncharged component. The microscopic approach is based on kinetic theory and is fully self-consistent. It allows to determine configurational prop- erties, such as layering near the confining walls, and the flow properties. We show that, under appropriate assumptions, the approach reproduces the phenomenological equations used to describe electrokinetic phenomena, without requiring the introduction of constitutive equations to determine the fluxes. Moreover, we model channels of arbitrary shape and nanometric roughness, features that have important repercussions on the transport properties of these systems. Numerical simulations are obtained by solving the evolution dynamics of the one-particle phase- space distributions of each species by means of a Lattice Boltzmann method for flows in straight and wedged channels. Results are presented for the microscopic density, the velocity profiles and for the volumetric and charge flow-rates. Strong departures from electroneutrality are shown to appear at molecular level.