A NEW GROWTH INSTABILITY IN COLLOIDAL CRYSTALLIZATION

SUSPENSIONS of monodisperse colloidal particles are useful model systems for studying order-disorder transitions. The bright iridescence of colloidal crystals, resulting from diffraction of visible light, is well-known 1-5. We have shown recently that this diffraction process depolarizes light sufficiently to reveal the orientation of the primary diffraction planes through the colours observed in a polarizing microscope 6,7. In the course of these investigations we have observed a new crystallization instability that can be explained, in part, by a diffusion-limited crystallization process. Although it is analogous to the mechanism of pattern formation in molecular systems, here the instability occurs for particles interacting solely by repulsive forces. We provide a qualitative explanation of the process using a classic Mullins-Sekerka 8 stability analysis. Our observations suggest that colloidal suspensions can provide a useful model not only for the study of crystallization thermodynamics but also for investigations of ordering dynamics.