A model for the generic alpha relaxation of viscous liquids

TL;DR

This paper proposes a theoretical model for the alpha relaxation in viscous liquids near the glass transition, explaining the universal high-frequency behavior and the influence of beta processes.

Contribution

It introduces a coupling-based model for dielectric alpha relaxation, solved in Gaussian approximation, capturing the generic features observed experimentally.

Findings

Reproduces the $\omega^{-1/2}$ high-frequency loss behavior.

Accounts for deviations due to beta processes.

Provides a theoretical framework for alpha relaxation dynamics.

Abstract

Dielectric measurements on molecular liquids just above the glass transition indicate that alpha relaxation is characterized by a generic high-frequency loss varying as $\omega^{-1/2}$, whereas deviations from this come from one or more low-lying beta processes [Olsen et al, Phys. Rev. Lett. {\bf 86} (2001) 1271]. Assuming that long-wavelength fluctuations dominate the dynamics, a model for the dielectric alpha relaxation based on the simplest coupling between the density and dipole density fields is proposed here. The model, which is solved in second order perturbation theory in the Gaussian approximation, reproduces the generic features of alpha relaxation.