Kinetics of colloidal heteroaggregation

Aggregation in a colloidal system composed of positive and negative particles is studied by simulations and theoretically. The system is comprised of a 50/50 mixture of particles with the same size and opposite charge. Brownian dynamics simulations are performed, varying the range of interaction to study the effect of interactions on the aggregation behavior. Homoaggregation results are recovered for very short range interactions, while important differences are observed when the interactions control the aggregation. It is found that cluster discrimination occurs at late stages of aggregation; neutral clusters are observed to disappear faster than charged ones. Also, the total number of clusters decay according to a power law, the exponent being a function of the interaction range. A theoretical model is developed to account for these effects. By introducing a two-fold homogeneous kernel, it is possible to reproduce most of the features of charge heteroaggregation.