Electrostatic interactions in charged nanoslits within an explicit solvent theory

TL;DR

This paper develops a non-linear electrostatic theory for charged nanoslits with explicit solvent modeling, revealing enhanced counterion adsorption and highlighting limitations of implicit solvent models in nanofluidic applications.

Contribution

It extends a Poisson-Boltzmann based approach to nanoslit geometry, incorporating explicit solvent effects and electrostatic correlations.

Findings

Enhanced electric fields near charged interfaces due to solvent structure.

Presence of an interfacial counterion adsorption layer.

Implicit solvent models are quantitatively inaccurate for ionic selectivity predictions.

Abstract

Within a dipolar Poisson-Boltzmann theory including electrostatic correlations, we consider the effect of explicit solvent structure on solvent and ion partition confined to charged nanopores. We develop a relaxation scheme for the solution of this highly non-linear integro-differential equation for the electrostatic potential. The scheme is an extension of the approach previously introduced for simple planes (S. Buyukdagli and Ralf Blossey, J. Chem. Phys. 140, 234903 (2014)) to nanoslit geometry. We show that the reduced dielectric response of solvent molecules at the membrane walls gives rise to an electric field significantly stronger than the field of the classical Poisson-Boltzmann equation. This peculiarity associated with non-local electrostatic interactions results in turn in an interfacial counterion adsorption layer absent in continuum theories. The observation of this enhanced counterion affinity in the very close vicinity of the interface may have important impacts on nanofludic transport through charged nanopores. Our results indicate the quantitative inaccuracy of solvent implicit nanofiltration theories in predicting the ionic selectivity of membrane nanopores.