Percolation in cluster-cluster aggregation processes.

Numerical simulations of Diffusion-Limited and Reaction-Limited ClusterCluster Aggregation processes of identical particles are performed in a twodimensional box. It is shown that, for concentrations larger than a characteristic gel concentration, the morphology of the resulting spanning cluster at the gel time tg exhibits a crossover length Lc between percolation (l > Lc) and aggregation (l < Lc). Lc vanishes when increasing c, and, at a critical concentration value cp (where Lc → 0) the entire spanning cluster scales as the percolating cluster obtained by standard percolation. Even if for c > cp the long-range correlations are similar to that of percolation, the vanishing links in the structure suggest that an homogeneous regime appears at small scales. PACS numbers: 61.43.H, 64.60.A Typeset using REVTEX 1