Spontaneous Crystallization in Systems of Binary Hard Sphere Colloids

TL;DR

This study demonstrates the spontaneous formation of binary hard sphere crystals, including Laves phases, from fluid states in simulations, revealing insights into crystallization mechanisms and stability regions.

Contribution

It provides the first simulation evidence of binary hard sphere crystal growth directly from fluid, including analysis of kinetics and phase diagrams.

Findings

Binary hard sphere crystals grow spontaneously from fluid in simulations.

Crystallization transitions from nucleation to spinodal decomposition.

State diagrams near stability regions of binary crystals are presented.

Abstract

Computer simulations of the fluid-to-solid phase transition in the hard sphere system were instrumental for our understanding of crystallization processes. But while colloid experiments and theory have been predicting the stability of several binary hard sphere crystals for many years, simulations were not successful to confirm this phenomenon. Here, we report the growth of binary hard sphere crystals isostructural to Laves phases, AlB$_2$, and NaZn$_{13}$ in simulation directly from the fluid. We analyze particle kinetics during Laves phase growth using event-driven molecular dynamics simulations with and without swap moves that speed up diffusion. The crystallization process transitions from nucleation and growth to spinodal decomposition already deep within the fluid-solid coexistence regime. Finally, we present packing fraction-size ratio state diagrams in the vicinity of the stability regions of three binary crystals.