# Density dependence of relaxation dynamics in glass formers, and the dependence of their fragility on the softness of inter-particle interactions

## TL;DR

This study investigates how the softness of inter-particle interactions influences the fragility of glass formers, revealing that softer particles tend to form more fragile glasses when analyzed through density-temperature scaling and Adam-Gibbs theory.

## Contribution

It demonstrates that the apparent relationship between interaction softness and fragility depends on the analysis method, clarifying the role of density-temperature scaling and the Adam-Gibbs framework.

## Key findings

- Softer interactions lead to stronger glass behavior when using inverse density.
- Using scaled variables involving temperature and density suggests the opposite.
- Within Adam-Gibbs theory, softer particles are more fragile.

## Abstract

Fragility, quantifying the rapidity of variation of relaxation times, is analysed for a series of model glass formers, which differ in the softness of their interparticle interactions. In an attempt to rationalize experimental observations in colloidal suspensions that softer interactions lead to stronger (less fragile) glass formers, we study the variation of relaxation dynamics with density, rather than temperature, as a control parameter. We employ density temperature scaling, analyzed in recent studies, to address the question. We find that while employing inverse density in place of temperature leads to the conclusion that softer interactions lead to stronger behaviour, the use of scaled variables involving temperature and density lead to the opposite conclusion, similarly to earlier investigations where temperature variation of relaxation dynamics was analysed for the same systems. We rationalize our results by considering the Adam-Gibbs (AG) fragility, which incorporates the density dependence of the configurational entropy and an activation energy that may arise from other properties of a glass former. Within the framework of the Adam-Gibbs relation, by employing density temperature scaling for the analysis, we find that softer particles make more fragile glasses, as deduced from dynamical quantities, which is found to be consistent with the Adam-Gibbs fragility.