Revealing the role of molecular rigidity on the fragility evolution of glass-forming liquids

TL;DR

This study uses molecular dynamics simulations to explore how molecular rigidity influences the fragility and relaxation behavior of glass-forming liquids, linking topological constraints to glass transition dynamics.

Contribution

It introduces a novel connection between molecular rigidity, topological constraints, and fragility in glass-forming liquids, extending the fragility concept to structural topology.

Findings

Relaxation behavior correlates with rigidity variation and topological constraints.

Fragility minima are connected to the spatial distribution of constraints.

The approach extends fragility analysis to atomic-scale topology.

Abstract

If quenched fast enough, a liquid is able to avoid crystallization and will remain in a metastable supercooled state down to the glass transition, with an important increase in viscosity upon further cooling. There are important differences in the way liquids relax as they approach the glass transition, rapid or slow variation in dynamic quantities under moderate temperature changes, and a simple means to quantify such variations is provided by the concept of "fragility". Here, we report molecular dynamics simulations of a typical network-forming glass, Ge-Se, and find that the relaxation behaviour of the supercooled liquid is strongly correlated to the variation of rigidity with temperature and the spatial distribution of the corresponding topological constraints which, ultimately connect to fragility minima. This permits extending the fragility concept to aspects of topology/rigidity, and to the degree of homogeneity of the atomic-sale interactions for a variety of structural glasses.