Surface Tension of Aqueous Electrolyte Solutions. A Thermomechanical Approach

TL;DR

This paper introduces a thermomechanical method to analytically calculate the surface tension of aqueous electrolyte solutions, accurately matching experimental data across various concentrations with minimal fitting parameters.

Contribution

It presents a novel thermomechanical approach deriving the stress tensor for inhomogeneous fluids, leading to an analytical expression for surface tension that aligns with classical laws and experimental results.

Findings

Analytical expression for surface tension derived in linear approximation.

The model reproduces the Onsager-Samaras limiting law at low concentrations.

Accurately fits experimental data for different interfaces with one fitting parameter.

Abstract

We determine the surface tension of aqueous electrolyte solutions in contact with non-polar dielectric media using a thermomechanical approach, which involves deriving the stress tensor from the thermodynamic potential of an inhomogeneous fluid. To obtain the surface tension, we calculate both the normal and tangential pressures using the components of the stress tensor, recently derived by us [Y. A. Budkov and P. E. Brandyshev, The Journal of Chemical Physics 159 (2023)] within the framework of Wang's variational field theory. Using this approach, we derive an analytical expression for the surface tension in the linear approximation. At low ionic concentrations, this expression represents the classical Onsager-Samaras limiting law. By utilizing only one fitting parameter, which is related to the affinity of anions to the dielectric boundary, we can approximate various experimental data regarding the surface tension of aqueous electrolyte solutions. This approximation applies to both the solution-air and solution-dodecane interfaces, covering a wide range of electrolyte concentrations.