Glassy dynamics and a growing structural length scale in supercooled nanoparticles

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.