Glassy dynamics and a growing structural length scale in supercooled nanoparticles

TL;DR

This study uses molecular dynamics simulations to explore how supercooled nanoparticles exhibit a decreasing glass transition temperature, coupled with growing structural length scales and relaxation times, influenced by particle size.

Contribution

It demonstrates the size-dependent lowering of glass transition temperature and links relaxation dynamics to local structural growth within a theoretical framework.

Findings

Glass transition temperature decreases as particle size shrinks.

Relaxation times grow with the development of local structural clusters.

Growth of structural length scales aligns with the Random First Order Transition model.

Abstract

We use molecular dynamics simulation to study the relationship between structure and dynamics in supercooled binary Lennard--Jones nanoparticles over a range of particle sizes. The glass transition temperature of the nanoparticles is found to be significantly lowered relative to the bulk, decreasing as $N^{-1/3}$ with decreasing particle size. This allows the nanoparticles to sample low energy states on the potential energy landscape and we are able to study their relaxation times, measured in terms of the intermediate scattering function, and their structure, measured in terms of locally favoured structures, to low temperatures. Our work shows that the growing relaxation times in the supercooled nanoparticles are coupled with the growth of physical clusters formed from favoured local structures in a way that is well described by the Random First Order Transition entropic droplet model, but with exponents that are dependent on the nanoparticle size.