Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene

TL;DR

This study measures depolarized light scattering in benzene across a wide temperature and frequency range, revealing structural relaxation phenomena similar to glass-forming materials, and demonstrates that simple liquids share underlying relaxation mechanisms.

Contribution

It shows that structural relaxation in simple liquids like benzene is fundamentally the same as alpha relaxation in glass-formers, using mode-coupling theory for data fitting.

Findings

Susceptibility peak due to structural relaxation observed between 40-180 GHz.

Peak exhibits stretching and time-temperature scaling similar to glass-formers.

Mode-coupling model fits the entire data set consistently.

Abstract

We have measured depolarized light scattering in liquid benzene over the whole accessible temperature range and over four decades in frequency. Between 40 and 180 GHz we find a susceptibility peak due to structural relaxation. This peak shows stretching and time-temperature scaling as known from $\alpha$ relaxation in glass-forming materials. A simple mode-coupling model provides consistent fits of the entire data set. We conclude that structural relaxation in simple liquids and $\alpha$ relaxation in glass-forming materials are physically the same. A deeper understanding of simple liquids is reached by applying concepts that were originally developed in the context of glass-transition research.