The critical role of entropy in glass transition kinetics

TL;DR

This study reveals that activation free energy and entropy are key to understanding glass transition temperature and fragility, providing a statistical framework for 150 glass-forming systems and explaining phenomena in confined or pressured glasses.

Contribution

It introduces a thermodynamic model linking activation parameters to glass transition temperature and fragility, advancing understanding of glass transition mechanisms.

Findings

Activation free energy determines Tg via G*/290+25.5

Activation entropy influences fragility m through S*/Rln10+15

Fragility reflects the degeneracy of evolution paths in energy landscapes

Abstract

Glass transition is a reversible transition that occurs in most amorphous materials. However, the nature of glass transition remains far from being clarified. A key to understand the glass transition is to clarify what determines the glass transition temperature (Tg) and liquid fragility (m). Here the glass transition thermodynamics for 150 different glass-forming systems are studied statistically. It is found that the activation characters in the energy landscape are crucial to precisely portray the glass transition and, in particular, both the activation free energy (G*) and the activation entropy (S*) play critical roles. G* determines Tg, Tg=G*/290+25.5, while S* determines m, m=S*/Rln10+15 with R is gas constant. Based on the Boltzmann definition of entropy, the fragility is an indication of the number of the degeneracy of the evolution paths. This explains why the nano-confined, low-dimension or high-pressured glasses exhibit stronger characteristics, which has been a puzzling phenomenon for a long time.