Scaling out the density dependence of the $\alpha$ relaxation in glassforming polymers

TL;DR

This paper demonstrates that the alpha relaxation in glassforming polymers can be unified under a single density-temperature scaling variable, suggesting fragility is an intrinsic property independent of density, and proposes a modification to the Angell plot.

Contribution

It introduces a density-temperature scaling approach for alpha relaxation times and redefines fragility as an intrinsic property, modifying the traditional Angell plot.

Findings

Relaxation times follow a single scaling variable $X=e( ho)/T$.

Fragility is density-independent and intrinsic to the material.

Proposes a modified Angell plot based on the scaling.

Abstract

We show that the density and temperature dependences of the $\alpha$-relaxation time of several glassforming polymers can be described through a single scaling variable $X=e(\rho)/T$, where $e(\rho)$ is well fitted by a power law $\rho^x$, $x$ being a species-specific parameter. This implies that ``fragility'' is an intrinsic, density-independent property of a glassformer characterizing its super-Arrhenius slowing down of relaxations, and it leads us to propose a modification of the celebrated Angell plot.