Does frequency-temperature superposition hold in deeply super-cooled liquids?

TL;DR

This study investigates whether the frequency-temperature superposition principle applies to deeply supercooled liquids by analyzing dielectric susceptibility across various frequencies and temperatures, revealing distinct relaxation processes and their temperature dependencies.

Contribution

It demonstrates that the alpha-process exhibits frequency-temperature superposition at all temperatures and distinguishes the excess wing from the beta-process in supercooled liquids.

Findings

Alpha-peak and wing have temperature-independent high-frequency exponents.

The excess wing's relaxation strength increases as temperature decreases.

A typical beta-process is identified in glycerol for the first time.

Abstract

The temperature evolution of the broadband $10^{-6}$-$10^{10}$ Hz dielectric susceptibility of the paradigmatic glass formers glycerol, propylene carbonate, and fluoro-aniline is analyzed assuming a three-step relaxation due to the $\alpha$-process, its excess wing, and a $\beta$-process. We find that the $\alpha$-peak and the wing can be described by susceptibility functions with temperature-independent high-frequency exponents, while the relative weight of these contributions does depend on the temperature. The excess wing and the $\beta$-process are distinct phenomena; in particular, the relaxation strength of the excess wing grows with decreasing the temperature, contrary to that of the $\beta$-process. In our interpretation, the frequency-temperature superposition of the $\alpha$-process is valid for all temperatures; in the case of glycerol, a typical $\beta$-process is unambiguously identified for the first time.