Kerr effect as a tool for the investigation of dynamic heterogeneities

TL;DR

This paper introduces a nonlinear Kerr effect experiment to differentiate between homogeneous and heterogeneous relaxation in glassy systems, providing a new method to analyze molecular dynamics.

Contribution

The study models Kerr effect responses for heterogeneous and homogeneous relaxations, demonstrating the experiment's ability to distinguish between these scenarios and analyze relaxation time distributions.

Findings

Kerr effect can differentiate relaxation types in glassy systems.

Exchange between environments does not hinder frequency-selective analysis.

Method reveals changes in relaxation time distribution width.

Abstract

We propose a dynamic Kerr effect experiment for the distinction between dynamic heterogeneous and homogeneous relaxation in glassy systems. The possibility of this distinction is due to the inherent nonlinearity of the Kerr effect signal. We model the slow reorientational molecular motion in supercooled liquids in terms of non-inertial rotational diffusion. The Kerr effect response, consisting of two terms, is calculated for heterogeneous and for homogeneous variants of the stochastic model. It turns out that the experiment is able to distinguish between the two scenarios. We furthermore show that exchange between relatively 'slow' and 'fast' environments does not affect the possibility of frequency-selective modifications. It is demonstrated how information about changes in the width of the relaxation time distribution can be obtained from experimental results.