Dendritic Growth of Hard Sphere Crystals

Recent observations of the disorder−order transition for colloidal hard spheres under microgravity revealed dendritic crystallites roughly 1−2 mm in size for samples in the coexistence region of the phase diagram. Order of magnitude estimates rationalize the absence of large or dendritic crystals under normal gravity and their stability to annealing in microgravity. A linear stability analysis of the Ackerson and Schätzel model for crystallization of hard spheres establishes the domain of instability for diffusion-limited growth at small supersaturations. The relationship between hard sphere and molecular crystal growth is established and exploited to relate the predicted linear instability to the well-developed dendrites observed.