Modeling non-linear dielectric susceptibilities of supercooled molecular liquids

TL;DR

This paper derives explicit models for non-linear dielectric susceptibilities in supercooled liquids, showing their non-monotonic behavior and agreement with experiments, challenging thermodynamic theories of dynamic arrest.

Contribution

It introduces a dynamic facilitation perspective to model non-linear susceptibilities, providing explicit expressions that match experimental data.

Findings

Non-linear susceptibilities exhibit non-monotonic frequency dependence.

Model predictions align well with experimental data for glycerol.

Results challenge thermodynamic-based theories of dynamic arrest.

Abstract

Advances in high-precision dielectric spectroscopy has enabled access to non-linear susceptibilities of polar molecular liquids. The observed non-monotonic behavior has been claimed to provide strong support for theories of dynamic arrest based on thermodynamic amorphous order. Here we approach this question from the perspective of dynamic facilitation, an alternative view focusing on emergent kinetic constraints underlying the dynamic arrest of a liquid approaching its glass transition. We derive explicit expressions for the frequency-dependent higher-order dielectric susceptibilities exhibiting a non-monotonic shape, the height of which increases as temperature is lowered. We demonstrate excellent agreement with the experimental data for glycerol, challenging the idea that non-linear response functions reveal correlated relaxation in supercooled liquids.