The effects of polydispersity and metastability on crystal growth kinetics

TL;DR

This study explores how metastable gas-liquid separation influences crystal growth in monodisperse and polydisperse particles, revealing that polydispersity affects growth rates and local ordering, emphasizing their combined importance in soft matter dynamics.

Contribution

It demonstrates the qualitative impact of metastable G-L separation on crystal growth and highlights the role of polydispersity in dynamic fractionation processes.

Findings

Gas layer coats the crystal during growth within the metastable binodal.

Polydispersity qualitatively alters the effect of G-L separation on growth rate.

Local size ordering and fractionation are facilitated by the gas layer.

Abstract

We investigate the effect of metastable gas-liquid (G-L) separation on crystal growth in a system of either monodisperse or slightly size-polydisperse square well particles, using a simulation setup that allows us to focus on the growth of a single crystal. Our system parameters are such that, inside the metastable G-L binodal, a macroscopic layer of the gas phase "coats" the crystal as it grows, consistent with experiment and theoretical free energy considerations. Crucially, the effect of this metastable G-L separation on the crystal growth rate depends qualitatively on whether the system is polydisperse. We measure reduced polydispersity and qualitatively different local size ordering in the crystal relative to the fluid, proposing that the required fractionation is dynamically facilitated by the gas layer. Our results show that polydispersity and metastability, both ubiquitous in soft matter, must be considered in tandem if their dynamical effects are to be understood.