GROWTH-KINETICS OF BODY-CENTERED-CUBIC COLLOIDAL CRYSTALS

A combination of static light scattering and video microscopy is used to perform high precision measurements on the growth velocity of body centered cubic (bcc) crystals in a metastable colloidal melt of monodi sperse, highly charged latex spheres. The crystals nucleate heterogene ously at the walls of a flat dow-through shear cell and solidification proceeds without significant disturbance by homogeneous nucleation. T he suspension parameters packing fraction Phi of the spheres and the c oncentration of screening electrolyte c are systematically varied for two kinds of particles with equal diameter but different charge. For a ll experimental conditions the growth velocities in the [110] directio n collapse on a single curve if plotted against a reduced energy densi ty difference II between the melt and the fluid at melting. Close to the phase boundary growth velocities vary linearly with increasing II , and saturate at large II at a value of upsilon(infinity) = 9.1 mu m s(-1). The master curve can be fitted excellently by a Wilson-Frenkel growth law which was suggested to hold for the solidification of high ly charged systems. A comparison of Coefficients allows for the deriva tion of a quantitative estimation procedure for the difference in chem ical potential Delta mu between melt and solid in terms of the thermal energy k(B)T: Delta mu = IIB. The best value for the conversion fact or B is found to be B =(6.7+/-0.1)k(B)T. In contrast to previous work on homogeneously nucleated crystals the growth velocity of the [110] f ace is limited by the reactionlike kinetics of registering preordered layers formed within an interface of finite thickness. We suggest a un ified description covering also the growth of the rough interfaces of other crystal faces.