Precursor-mediated crystallization process in suspensions of hard spheres

TL;DR

This study uses large-scale computer simulations to demonstrate that hard sphere suspensions crystallize through a two-step process involving dense amorphous clusters acting as precursors, a mechanism previously thought exclusive to systems with attractive interactions.

Contribution

It reveals that a purely repulsive hard sphere system undergoes a two-step crystallization process, challenging the belief that metastable fluid-fluid coexistence is necessary for such mechanisms.

Findings

Crystallization occurs via dense amorphous clusters forming first.

The two-step process is observed in purely repulsive systems.

Mechanism previously associated with attractive interactions also applies here.

Abstract

We report on a large scale computer simulation study of crystal nucleation in hard spheres. Through a combined analysis of real and reciprocal space data, a picture of a two-step crystallization process is supported: First dense, amorphous clusters form which then act as precursors for the nucleation of well-ordered crystallites. This kind of crystallization process has been previously observed in systems that interact via potentials that have an attractive as well as a repulsive part, most prominently in protein solutions. In this context the effect has been attributed to the presence of metastable fluid-fluid demixing. Our simulations, however, show that a purely repulsive system (that has no metastable fluid-fluid coexistence) crystallizes via the same mechanism.