Disentangling density and temperature effects in the viscous slowing down of glassforming liquids

TL;DR

This paper clarifies the roles of density and temperature in the viscous slowdown of glass-forming liquids, emphasizing temperature-driven super-Arrhenius behavior over density-driven jamming, with implications for understanding glass transition dynamics.

Contribution

It provides a unified analysis showing that temperature primarily governs the glass transition, with density effects being quantitatively minor and describable by a single effective interaction parameter.

Findings

Viscosity is mainly controlled by temperature, not density.

Density effects can be captured by an effective interaction energy.

Fragility is unaffected by density variations.

Abstract

We present a consistent picture of the respective role of density and temperature in the viscous slowing down of glassforming liquids and polymers. Specifically, based in part upon a new analysis of simulation and experimental data on liquid ortho-terphenyl, we conclude that a zeroth-order description of the approach to the glass transition should be formulated in terms of a temperature-driven super-Arrhenius activated behavior rather than a density-driven congestion or jamming phenomenon. The density plays a role at a quantitative level, but its effect on the viscosity and the structural relaxation time can be simply described via a single parameter, an effective interaction energy that is characteristic of the high temperature liquid regime; as a result, density does not affect the ``fragility'' of the glassforming system.