Universality of Fractal Aggregates as Probed by Light Scattering

Fractal colloid aggregates are studied with both static and dynamic light scattering. The dynamic light scattering data are scaled onto a single master curve, whose shape is sensitive to the structure of the aggregates and their mass distribution. By using the structure factor determined from computer-simulated aggregates, and including the effects of rotational diffusion, we predict the shape of the master curve for different cluster distributions. Excellent agreement is found between our predictions and the data for the two limiting regimes, diffusion-limited and reaction-limited colloid aggregation. Furthermore, using data from several completely different colloids, we find that the shapes of the master curves are identical for each regime. In addition, the cluster fractal dimensions and the aggregation kinetics are identical in each regime. This provides convincing experimental evidence of the universality of these two regimes of colloid aggregation.