Dynamics of crystallization in hard-sphere suspensions.

Abstract

Density fluctuations are monitored by small-angle light scattering during the crystallization of 0.22-\ensuremath{\mu}m-radius, hard colloidal spheres. Measured structure factors show an intensity maximum at finite-scattering vectors. The shape of the intensity distribution scales at early times during nucleation and growth and again at large times during ripening. At intermediate times there is a crossover region where scaling ceases to be valid. Both the amplitude and the position of the maximum intensity show quasi-power law behavior in time. The values of the observed exponents are within the range expected for classical growth models. The breadth of the intensity distribution increases with increasing volume fraction, suggesting greater crystal polydispersity with increasing volume fraction. The lower volume fraction intensity distributions suggest that crystals have a compound or internal structure, while the observed decrease in characteristic length in the crossover time regime may indicate breakup of crystals to this smaller internal structure. The results of measurements are compared with results calculated for nucleation and growth of crystals in suspensions of hard spheres. Results also are compared with earlier measurements made on samples containing 0.50-\ensuremath{\mu}m radius spheres. Differences in the two systems are discussed in terms of interparticle potential, polydispersity, and gravitational effects. \textcopyright{} 1996 The American Physical Society.