Crystallization kinetics of suspensions of hard colloidal spheres

The crystallization of suspensions of sterically stabilized polymer particles, with hard-sphere-like interactions, is studied by laser light scattering. Over the range of volume fractions examined, from just below melting to the glass transition, crystallization occurs by homogeneous nucleation. After the suspensions are shear melted, the intensity, position, and width of the main interlayer Bragg reflection are measured as functions of time. From these the amount of crystal, the average linear crystal dimension, the number of crystals, and the volume fraction of the crystal phase are obtained. No assumptions are made concerning the functional time dependence of nucleation or growth processes. Below the melting concentration the observed crystallization process is compatible with the classical picture of sequential nucleation and growth of isolated crystals. However, when the melting concentration is exceeded, nucleation events are correlated, nucleation is accelerated, and high nucleation rate densities suppress crystal growth. Above the melting concentration we infer, with the aid of the equations of state for the hard-sphere fluid and solid, that the first identifiable crystals are in mechanical equilibrium with the embedding fluid and, consequently, strongly compressed by it. Ensuing nucleation lags expansion of the crystal lattice.