Shear-driven aggregation of binary colloids for randomly distributing nanoparticles in a matrix

We propose a methodology for preparing composite materials where A nanoparticles (NPs) are uniformly and randomly distributed inside a matrix of B NPs. It is based on intense shear-driven aggregation of binary colloids composed of A and B NPs, without using any additives. Its feasibility has been demonstrated using stable binary colloids composed of poly-methyl methacrylate (PMMA) particles and polystyrene (PS) particles. The PS particles alone undergo shear-driven aggregation (shear-active), while the PMMA particles alone do not exhibit any aggregation under the same conditions (shear-inactive). It is found that the shear-driven aggregation of the binary colloids does occur, and the formed clusters are composed of both the "shear-active" PS and "shear-inactive" PMMA particles. The SEM pictures demonstrate that the PMMA particles are uniformly and randomly distributed among the PS particles in the clusters, thus confirming the feasibility of the proposed methodology. The mechanism leading to the aggregation of the binary colloids has been discussed based on the experimental observations.