Interdiffusion and crystallization of oppositely charged colloids.

The aggregation of oppositely charged colloids, usually denoted as heteroaggregation, is often used in colloidal processing, for which a precise control of the basic mechanisms of aggregate formation is of crucial importance. A promising way to achieve a better degree of control is to guide heteroaggregation by imposing geometric constraints. Here, we consider this possibility by simulating the heteroaggregation of two oppositely charged suspensions which are initially separated and then put into contact through a planar interface. Our Brownian dynamics simulations show that this type of heteroaggregation allows the formation of mixed films whose thickness can be controlled by tuning the interactions between the particles or by changing the colloidal concentration in the initial suspensions. The dependence of the type of crystalline order in these films on these parameters is also analyzed.