Simulation of a Solid-Solid Transition in Confined Colloidal Hard Spheres

Recent experiments on a system of colloidal particles confined between two flat plates showed a two-stage nucleation process involving the transition of a solid, consisting of n$+$1 crystalline layers with a square symmetry (n$+$1 s-phase), to another solid consisting of n triangular layers (n t-phase), via an intermediate metastable liquid droplet [1]. Using event-driven molecular dynamics and Monte Carlo simulations, we study the 5s $\to $ 4t solid-solid transition in colloidal hard spheres confined between two planar hard walls. The 5s solid initially melts, forming a liquid droplet, within which the 4t solid nucleates. Calculations of the free-energy landscape confirm that the optimal kinetic pathway is a two-stage nucleation process with a critical nucleus consisting of liquid-like and t-solid-like particles. In addition, we find that the t-solid-like cluster nucleates near the planar hard walls, and contains both face-centered-cubic and hexagonal-close-packed ordered particles. \\[4pt] [1] Y. Peng, F. Wang, Z. Wang, A. M. Alsayed, Z. Zhang, A. G. Yodh and Y. Han, Nature Materials, In press (2014).