Ionic conductivity on a wetting surface

TL;DR

This paper presents a theoretical model explaining the humidity-dependent ionic conductivity on charged surfaces, specifically DNA, based on ion pair unbinding influenced by water adsorption.

Contribution

A simple theoretical framework is introduced to describe ion transport on wetting surfaces, emphasizing the role of water-induced electrostatic energy reduction.

Findings

Conductivity increases with humidity due to water layer effects.

Model predictions align with experimental data within certain limits.

Electrostatic self-energy decreases as water adsorbs, facilitating ion unbinding.

Abstract

Recent experiments measuring the electrical conductivity of DNA molecules highlight the need for a theoretical model of ion transport along a charged surface. Here we present a simple theory based on the idea of unbinding of ion pairs. The strong humidity dependence of conductivity is explained by the decrease in the electrostatic self-energy of a separated pair when a layer of water (with high dielectric constant) is adsorbed to the surface. We compare our prediction for conductivity to experiment, and discuss the limits of its applicability.