On the correlation between fragility and stretching in glassforming liquids

TL;DR

This study investigates the relationship between fragility and stretching in glassforming liquids by analyzing dielectric relaxation data, proposing that a meaningful correlation exists between these properties under specific conditions.

Contribution

It provides new insights into the correlation between fragility and stretching, emphasizing the importance of isochoric conditions for understanding their intrinsic relationship.

Findings

Fragility and stretching are correlated under isochoric conditions.

Both properties remain constant under isochronic conditions.

The study suggests constraints for empirical correlations in glassformers.

Abstract

We study the pressure and temperature dependences of the dielectric relaxation of two molecular glassforming liquids, dibutyl phtalate and m-toluidine. We focus on two characteristics of the slowing down of relaxation, the fragility associated with the temperature dependence and the stretching characterizing the relaxation function. We combine our data with data from the literature to revisit the proposed correlation between these two quantities. We do this in light of constraints that we suggest to put on the search for empirical correlations among properties of glassformers. In particular, argue that a meaningful correlation is to be looked for between stretching and isochoric fragility, as both seem to be constant under isochronic conditions and thereby reflect the intrinsic effect of temperature.