Surface tensions, surface potentials and the Hofmeister series of electrolyte solutions

TL;DR

This paper presents a comprehensive theory that accurately predicts surface tensions and potentials of electrolyte solutions, incorporating ionic hydration and polarizability, and successfully explains the Hofmeister series.

Contribution

The study introduces a novel theoretical model that quantitatively links ionic properties to surface phenomena, with only one adjustable parameter, advancing understanding of electrolyte interfaces.

Findings

Strong correlation between hydration and surface behavior of ions.

Kosmotropic ions are strongly hydrated and repelled from the interface.

Chaotropic ions are adsorbed at the interface, following the Hofmeister series.

Abstract

A theory is presented which allows us to accurately calculate the surface tensions and the surface potentials of electrolyte solutions. Both the ionic hydration and the polarizability are taken into account. We find a good correlation between the Jones-Dole viscosity $B$-coefficient and the ionic hydration near the air-water interface. The kosmotropic anions such as fluoride, iodate, sulfate and carbonate, are found to be strongly hydrated and are repelled from the interface. The chaotropic anions such as perchlorate, iodide, chlorate and bromide are found to be significantly adsorbed to the interface. Chloride and bromate anions become weakly hydrated in the interfacial region. The sequence of surface tensions and surface potentials is found to follow the Hofmeister ordering. The theory, with only one adjustable parameter, quantitatively accounts for the surface tensions of 10 sodium salts for which there is experimental data.