(749d) The Role of Interaction Heterogeneity in Colloidal Crystallization
The beneficial impact of population-wide interaction heterogeneity is shown to arise from a synergistic combination of two effects. First, we employ equilibrium umbrella sampling simulations to show that heterogeneity lowers the free energy barrier associated with the nucleation of crystals by the formation of strongly-bound small clusters, even if the overall average binding energy between pairs of particles is held constant. This finding is confirmed by direct, non-equilibrium crystal growth simulations, which demonstrate that crystallization proceeds over a wider range of average interaction energy. On the other hand, these simulations also show that variations in the interaction strength between particles inhibit gelation and polycrystallinity by keeping the number of stable nuclei low, allowing individual nuclei to grow unhindered. In combination, these effects lead to a âspreading-outâ of the nucleation process and a concomitant widening of the crystallization window. These results are used to investigate potential avenues for intentionally controlling the nucleation rate in colloidal crystallization experiments.