Dielectric response as a source of viscosity in polar liquids

TL;DR

This paper demonstrates that in polar liquids, dielectric relaxation significantly influences shear viscosity, establishing a quantitative link between dielectric properties and rheological behavior.

Contribution

It introduces a theoretical framework connecting dielectric response parameters to viscosity, predicting temperature-dependent viscosity in polar liquids from dielectric data.

Findings

Dielectric relaxation contributes substantially to shear viscosity in polar liquids.

The theory accurately predicts viscosity temperature dependence for water and alcohols.

A universal mechanism links slow polarization dynamics to increased viscosity.

Abstract

Transport coefficients and dielectric relaxation in liquids are often treated as distinct manifestations of molecular dynamics. We show that, in polar liquids, orientational dipolar fluctuations generate a substantial contribution to the shear viscosity that can be expressed in terms of dielectric response parameters. Using a Green-Kubo approach formulated in terms of dipolar body-force correlations, we derive an explicit relation linking the viscosity increment to the static permittivity and the Debye relaxation time. With a single microscopic cutoff length fixed from one temperature, the theory predicts the temperature dependence of the viscosity for water and several alcohols using independently measured dielectric data. The results identify a general mechanism by which slow polarization dynamics generate an additional, and in strongly polar liquids often dominant, contribution to the viscosity, providing a quantitative bridge between dielectric spectroscopy and rheology.