CLUSTER-CLUSTER GELATION WITH FINITE BOND-ENERGY

Aggregation and gelation of colloidal particles in two and three dimensions is simulated using the diffusion-limited cluster-cluster aggregation model with a finite interparticle bonding energy. Particles and clusters break apart due to thermal fluctuations in kinetic energy. The effects on the structure of the aggregating system as a whole are studied via methods analogous to light-scattering in experiments. We consider relatively weak interparticle attractive potentials E of the order of a few times the thermal fluctuation energy k(B)T. In irreversible aggregation the system of clusters forms a gel, a space-filling connected structure. We find that given strong enough bonding the assembly of clusters still approaches gelation (the assembly fills an increasing fraction of space) but the 'gel' structure is markedly different from the case where bonding is irreversible. At lower energies a sol of clusters is formed, the clusters being internally compact with ramified surfaces. At late time one expects the system to evolve to a pattern of coarsening, near-compact droplets familiar from general first-order phase transition and phase separation studies.