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 t(g) exhibits a crossover length L(c) between percolation (l > L(c)) and aggregation (l < L(c)). L(c) vanishes when increasing c, and, at a critical concentration value c(p) similar or equal to 0.5 (where L(c) --> 0) the entire spanning cluster scales as the percolating cluster obtained by standard percolation. Even if for 0.5 < c < 0.8 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.