MEASUREMENTS OF CLUSTER-SIZE DISTRIBUTIONS ARISING IN SALT-INDUCED AGGREGATION OF POLYSTYRENE MICROSPHERES

We have measured the temporal evolution of cluster-size distributions cn(t) during salt-induced aggregation of polystyrene microspheres, 258 nm in radius. Two regimes of irreversible aggregation were studied: fast aggregation (W = 1.9) and slow aggregation (W = 420). Distributions were measured using a single-particle light-scattering technique. At long times, we find that cn(t) for both fast and slow aggregation exhibits a dynamic scaling form given by cn(t) ∼ s-2φ(n/s). For fast aggregation, s(t) ∼ n̄n(t) the number-average mean cluster size, φ(x) is bell-shaped with a peak occuring at x ≈ 0.1, and s(t) ∼ t. For fast slow aggregation, s(t) ∼ nn2(t) ∼ t2, φ(x) decrease monotonically with x, and for x < 1, φ(x) ∼ x-1.5. We interpret our results using the Smoluchowski rate equation, which enables us to quantify the measured distributions in terms of two key parameters. © 1992.