Surface Tension of Electrolyte Solutions: A Self-consistent Theory

TL;DR

This paper presents a self-consistent field-theoretical model for electrolyte solution surface tension, reconciling classical results with ionic specificity and experimental data across various salts and concentrations.

Contribution

It introduces an analytical, self-consistent approach that extends the Onsager-Samaras theory to include ionic specificity and surface interactions, improving agreement with experiments.

Findings

The model reproduces the reverse Hofmeister series for anions.

It fits experimental data across a wide concentration range.

The Onsager-Samaras result is shown to be consistent with one-loop corrections.

Abstract

We study the surface tension of electrolyte solutions at the air/water and oil/water interfaces. Employing field-theoretical methods and considering short-range interactions of anions with the surface, we expand the Helmholtz free energy to first-order in a loop expansion and calculate the excess surface tension. Our approach is self-consistent and yields an analytical prediction that reunites the Onsager-Samaras pioneering result (which does not agree with experimental data), with the ionic specificity of the Hofmeister series. We obtain analytically the surface-tension dependence on the ionic strength, ionic size and ion-surface interaction, and show consequently that the Onsager-Samaras result is consistent with the one-loop correction beyond the mean-field result. Our theory fits well a wide range of concentrations for different salts using one fit parameter, reproducing the reverse Hofmeister series for anions at the air/water and oil/water interfaces.10.1029