Dependence of the dielectric constant of electrolyte solutions on ionic concentration - a microfield approach

TL;DR

This paper introduces a microfield model to predict how the dielectric constant of electrolyte solutions varies with salt concentration and temperature, accurately matching experimental data across different salts and concentrations.

Contribution

The study develops a new microfield approach that accounts for solvent dipole orientation and thermal fluctuations, providing a precise dielectric functional dependence for electrolyte solutions.

Findings

Accurately predicts dielectric constant dependence on salt concentration.

Matches experimental data for various salts and concentrations.

Provides a functional form consistent with observed dielectric behavior.

Abstract

We present a novel microfield approach for studying the dependence of the orientational polarization of the water in aqueous electrolyte solutions upon the salt concentration and temperature. The model takes into account the orientation of the solvent dipoles due to the electric field created by ions, and the effect of thermal fluctuations. The model predicts a dielectric functional dependence of the form $\varepsilon(c)=\varepsilon_w-\beta L(3\alpha c/\beta),\quad\beta=\varepsilon_w-\varepsilon_{\rm ms}$, where $L$ is the Langevin function, $c$ is the salt concentration, $\varepsilon_w$ is the dielectric of pure water, $\varepsilon_{\rm ms}$ is the dielectric of the electrolyte solution at the molten salt limit, and $\alpha$ is the total excess polarization of the ions. The functional form gives a remarkably accurate description of the dielectric constant for a variety of salts and a wide range of concentrations.