Two-Step Crystallization Kinetics in Colloidal Hard-Sphere Systems

The crystallization kinetics of colloidal hard spheres was studied using a special Bragg spectrometer with high sensitivity. In contrast with the classical scenario we observe a two-step nucleation process: the number of crystallites increases slowly at early times, followed by a dramatic reduction at intermediate times, prior to undergoing a rapid increase at late times. We explain these results in terms of a polydispersity limited growth of crystallites, where the crystallization at early times is governed by local fractionation processes, leading to a long delay prior to final crystallization.

Figure 1

Crystalline structure factors at a volume fraction near melting ($\varphi =0.538$) during the three time intervals (a) induction, (b) conversion, and (c) final nucleation. Note the different scales.

Figure 2

Extracted parameters from the data shown in Fig. 1: (a) nucleation rate densities; (b) absolute number of crystals (filled circles, left axis), crystalline volume fraction (open stars, right axis); (c) crystallinity (filled triangles, left axis), average linear dimension (open diamonds, right axis).

Figure 3

Average (open symbols) and maximum (filled symbols) nucleation rate densities as a function of volume fraction. (a) the first crystallization process and (b) the second crystallization process. The solid curve is a fit using CNT with ${\gamma }^{*}=0.5(2a{)}^2/kT$.