Ionic profiles close to dielectric discontinuities: Specific ion-surface interactions

TL;DR

This paper develops a field-theoretic approach to calculate ionic profiles near dielectric interfaces, incorporating short-range ion-surface interactions and correlation effects beyond mean-field theory, with implications for understanding surface tension and ion adsorption.

Contribution

It introduces a method to analytically compute ionic profiles near dielectric discontinuities considering non-linear boundary conditions and correlation effects, advancing beyond traditional mean-field approaches.

Findings

Ionic profiles depend on ion-surface interactions and dielectric properties.

Surface tension calculations align with the reverse Hofmeister series.

A single adhesivity parameter can predict ionic profiles from surface tension measurements.

Abstract

We study, by incorporating short-range ion-surface interactions, ionic profiles of electrolyte solutions close to a non-charged interface between two dielectric media. In order to account for important correlation effects close to the interface, the ionic profiles are calculated beyond mean-field theory, using the loop expansion of the free energy. We show how it is possible to overcome the well-known deficiency of the regular loop expansion close to the dielectric jump, and treat the non-linear boundary conditions within the framework of field theory. The ionic profiles are obtained analytically to one-loop order in the free energy, and their dependence on different ion-surface interactions is investigated. The Gibbs adsorption isotherm, as well as the ionic profiles are used to calculate the surface tension, in agreement with the reverse Hofmeister series. Consequently, from the experimentally-measured surface tension, one can extract a single adhesivity parameter, which can be used within our model to quantitatively predict hard to measure ionic profiles.