Multiple time scales and cluster formation mechanisms in charge-heteroaggregation processes

Abstract

We report simulation and experimental evidence of multiple cluster-formation mechanisms arising in coagulation in a binary mixture composed of oppositely charged colloids with large asymmetry in the relative particle concentration. These mechanisms can be clearly distinguished from one another as they cause the appearance of several maxima in the cluster-size distribution curves at well-separated time scales. We show that this behavior is caused by the fact that clusters of a given size can have different internal compositions. Moreover, the peaks collapse into a single maximum when electrostatic interactions are screened, which is a confirmation that this effect is very sensitive to the strength and range of the interparticle electrostatic interactions. The experimental confirmation of the simulation results represents the first evidence of non bell-shaped cluster-size distribution curves.