Structure factors from cluster-cluster aggregation simulation at high concentration

Aggregation of particles in two dimensions at high concentration is simulated using the diffusion-limited cluster-cluster aggregation model. Static structure factors are calculated from particle configurations. A simple model in which clusters diffuse at rates inversely proportional to their radii of gyration reproduces qualitatively the behaviour observed in experiments. A peak in the structure factor S(Q) is observed at small scattering vectors Q. The intensity of the peak increases, and its Q-value decreases, as the aggregation proceeds. Finally all particles belong to a single system-spanning cluster, the ‘gel’ state, and the scattering peak is ‘frozen’ at a given Q. The gel structure is formed from a random close-packed collection of smaller, ramified clusters.