Percolation in cluster-cluster aggregation processes

Numerical simulations of diffusion-limited and reaction-limited cluster-cluster aggregation processes of identical particles are performed in a two-dimensional 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 Ic between percolation (l>Lc) and aggregation (lLc). Lc vanishes when increasing c, and, at a critical concentration value cₚ{}0.5 (where Lc{→}0) the entire spanning cluster scales as the percolating cluster obtained by standard percolation. Even if for 0.5c0.8 the long-range correlations seem to be similar to that of percolation, the scaling mass analysis and the vanishing links in the structure suggest that a homogeneous regime appears at small scales. {} 1996 The American Physical Society.