Selective solvation in aqueous mixtures: Interface deformations and instability

TL;DR

This paper reviews how selective ion solvation affects aqueous mixture interfaces, showing that electrostatic and solvation interactions can drastically reduce surface tension and induce surface instabilities, especially near critical points.

Contribution

It introduces a theoretical framework for understanding interface deformations caused by ion solvation and electrostatics, highlighting conditions for surface instability in aqueous mixtures.

Findings

Surface tension can be significantly decreased by ion interactions.

Surface instability occurs when surface tension becomes negative.

Simulations demonstrate the onset of surface deformations due to ion effects.

Abstract

We briefly review the effects of selective solvation of ions in aqueous mixtures, where the ion densities and the composition fluctuations are strongly coupled. We then examine the surface tension \gamma of a liquid-liquid interface in the presence of ions. We show that \gamma can be decreased drastically due to the electrostatic and solvation interactions near the interface. We calculate how the free energy is changed due to small surface undulations in the presence of an electric double layer. A surface instability occurs for negative \gamma, which can easily be realized for antagonistic ion pairs near the solvent criticality. Three-dimensional simulation shows how the surface instability is induced.