Morphology selection kinetics of crystallization in a sphere

Crystallization under geometrical confinement is of fundamental importance in condensed matter physics, biophysics and material science. Even the influence of the simplest geometry, a sphere, on crystallization remains far from well understood, thereby making morphology control of the final superstructures challenging. Here, we employ charged colloids encapsulated in an emulsion droplet as a model system to access the crystallization kinetics at the single-particle level. We find rapid formation of ‘skin’ layers with an icosahedral arrangement of defects under the geometrical frustration effect, followed by interior ordering and slow ripening. The final morphologies are determined by dynamical interplay between the system-independent skin layer formation and the system-dependent structural transformation towards the most stable solid far from the surface. We reveal the crucial role of kinetics in morphological selection under a geometrical constraint, besides the thermodynamics, which may shed new light on the structural design of nanoscale crystals. The authors investigate the role of spherical confinement and curvature-induced topological defects on the crystallization of charged colloids. They conclude that crystallization in spherical confinement is due to a combination of thermodynamics and kinetic pathways.