Prevalence of approximate square root t relaxation for the dielectric alpha process in viscous organic liquids

TL;DR

This study analyzes dielectric relaxation in organic glass-forming liquids, revealing that most exhibit a near -1/2 slope in their alpha process, indicating approximate square-root-time relaxation as a common feature.

Contribution

It provides a comprehensive analysis of dielectric loss data, establishing the prevalence of approximate square-root-time relaxation in organic glass formers and exploring its correlations with various physical parameters.

Findings

Most liquids show minimum slopes close to -1/2.

Approximate sqrt(t) relaxation is a common property of alpha relaxation.

Large-loss liquids deviate from this behavior, showing larger slopes.

Abstract

This paper presents dielectric relaxation data for organic glass-forming liquids compiled from different groups and supplemented by new measurements. The main quantity of interest is the "minimum slope" of the $\alpha$ dielectric loss plotted as a function of frequency in a log-log plot (i.e., the numerically largest slope above the loss peak frequency). The data consisting of 347 spectra for 53 liquids show prevalence of minimum slopes close to -1/2, corresponding to approximate square-root-time dependence of the dielectric relaxation function at short times. The paper further studies possible correlations between minimum slopes and: 1) Temperature quantified via the loss-peak frequency; 2) How well an inverse power law fits data above the loss peak; 3) Degree of time-temperature superposition; 4) Loss-peak half width; 5) Deviation from non-Arrhenius behavior; 6) Loss strength. For the first three points we find correlations that indicate a special status of liquids with minimum slopes close to -1/2. For the last three points only fairly insignificant correlations are found with the exception of large-loss liquids, which have minimum slopes that are numerically significantly larger than 1/2 and loss peak widths that are significantly smaller than those of most other liquids. We conclude that -- excluding large-loss liquids -- approximate $\sqrt t$ relaxation appears to be a generic property of the $\alpha$ relaxation of organic glass formers.