Dielectric constant of mixed solvents based on perturbation theory

Abstract

Industrial applications such as batteries and bio-separations require modeling the thermodynamic properties of mixed solvent electrolytes. Thermodynamic models for electrolytes often consider the solvents as a dielectric continuum characterized by their dielectric constant. Therefore, accurate predictions require a physically sound model for the dielectric constant of mixed solvents, depending on temperature, pressure, and mixture composition. We present a physical model for the dielectric constant of pure solvents and mixtures based on perturbation theory. The analytical expression is third order in the dipole density. For each pure component, the model requires the dipole moment and two adjustable pure-component parameters. We apply the model to the binary mixtures methanol–water and ethylene glycol–water considering pure component experimental data for temperatures between 273.15 K to 823.15 K and pressures between 0.1 MPa and 1189.0 MPa. The presented model improves the prediction of the mixed solvent dielectric constant for both mixtures compared to the linear molar mixing rule, and achieves similar accuracies as the linear volume-based and mass-based mixing rules. We show that the model is suitable in the case of scarce experimental data.