Kinetics of crystal growth in charged colloidal suspensions

Abstract

We report on the solidification of a metastable colloidal melt of monodisperse, highly charged latex spheres. Light-scattering and video microscopy are used to study the growth velocities of crystals nucleated at the walls of the observation cell and in the bulk melt. The velocity observed for the planar (110) face of the body-centered cubic wall crystals v₁₁₀ is found to be significantly smaller than the radial growth velocity v _R of the homogeneously nucleated crystals of rounded polyhedric shape. Under isothermal conditions the interaction determining suspension parameters packing fraction Φ salt concentration c, and surface charge Z were systematically varied with high accuracy using advanced preparation methods. Growth velocities v ₁₁₀ in the 〈110〉 direction increase over more than three orders of magnitude with increasing Φ and decreasing c. All data collapse on a single curve if plotted against a reduced energy density Π* between melt and fluid at melting. This master curve shows an initially linear increase and saturates at large Π* with \gu_\t8=9.1\gmms^-1=9.1 µms⁻¹ as the limiting velocity. It can be excellently fitted with a Wilson-Frenkel growth law yielding a conversion factor of B=6.7 k _B T between Π* and the chemical potential difference Δμ between melt and solid. Detailed analysis of the saturation value \gu_\t8 provides evidence for two different growth mechanisms operative in the solidification of colloidal crystals