Computer Design of Materials: PUBLICATIONS

The structure and aggregation kinetics of 3-dimensional clusters composed of two different monomeric species at three concentrations are thoroughly investigated by means of extensive, large scale computer simulations. The aggregating monomers have all the same size and occupy the cells of a cubic lattice. Two bonding schemes are considered: (a) the binary diffusion-limited cluster-cluster aggregation (BDLCA) in which only the monomers of different species stick together, and (b) the invading binary diffusion-limited cluster-cluster aggregation (IBDLCA) in which additionally monomers of one of the two species are allowed to bond. In the two schemes the mixed aggregates display self similarity with a fractal dimension d_f that depends on the relative molar fraction of the two species and on concentration. At a given concentration, when this molar fraction is small, d_f approaches a value close to the reaction-limited cluster-cluster aggregation of one component systems, and when the molar fraction is 0.5 d_f becomes close to the value of the diffusion-limited cluster-cluster aggregation model. The crossover between these two regimes is due to a time decreasing reaction probability between colliding particles, particularly at small molar fractions. Several dynamical quantities are studied as a function of time. The number of clusters and the weight-average cluster size display a power law behavior only at small concentrations. The dynamical exponents are obtained for molar fractions above 0.3 but not at or below 0.2, indicating the presence of a critical transition between a gelling to a non-gelling system. The cluster size distribution function presents scaling for molar fractions larger than 0.2.