Limits of the Fractal Dimension for Irreversible Kinetic Aggregation of Gold Colloids

We show that there are two regimes of irreversible, kinetic aggregation of aqueous colloids, determined by the short-range interparticle potential, through its control of the sticking probability upon approach of two particles. Each regime has different rate-limiting physics, aggregation dynamics, and cluster-mass distributions, and results in clusters with different fractal dimensions. These results set limits on the fractal dimension, d₅, for gold aggregates of 1. 75<~d₅<~2. 05 (0. 05).