LOCAL ORDER IN 2-DIMENSIONAL COLLOIDAL AGGREGATION

Diffusion limited cluster-cluster aggregation in two dimensions has be en studied both experimentally and in computer simulation. In both cas es the structure function at late times exhibits hitherto unsuspected sixfold symmetry. The triangular structure of the system in real space is not very pronounced, resembling the local order of a liquid. The s ix peaks in the structure function lie at the wave number of the chara cteristic spatial modulation previously found for this system. It is a rgued that both phenomena arise due to mutually exclusive depletion zo nes which form around clusters in diffusion limited aggregation, provi ding an effective long-range intercluster repulsion.