Preparation of polymeric/inorganic nanocomposite particles in miniemulsions: I. Particle formation mechanism in systems stabilized with sodium dodecyl sulfate

Polymeric/inorganic nanocomposite particles (NCPs) were tentatively prepared through miniemulsion polymerization using sodium dodecyl sulfate (SDS) as the sole surfactant. The representative inorganic nanoparticles (NPs), SiO 2 NPs, were pre-dispersed in monomer solutions. Particle morphology and size of the latex particles in the emulsions prepared from miniemulsions were investigated in terms of the SiO 2 and SDS content. The results indicate that the number fraction of polymer/SiO 2 NCPs ( f NCP ) in the latex particles was below 4%, and that plain polymer particles dominated in all of the emulsions regardless of the SiO 2 and SDS content when the sonication power was 95   W. The centrifugation experiments showed that there were three types of particles in the emulsions, namely, a dominant amount of plain polymer particles, a small amount of polymer/SiO 2 NCPs, and a very small amount of sub-micrometer polymer/SiO 2 aggregates. These particles evolved from small plain monomer droplets, medium monomer droplets containing SiO 2 NPs, and micrometer monomer droplets containing many SiO 2 NPs, respectively. Formation mechanisms of these three types of particles were proposed. On the basis of the mechanism, we used higher sonication power to improve the homogeneity of the number distribution of SiO 2 NPs among monomer droplets. The f NCP value markedly increased to ∼39% upon increase of the sonication power to 190   W. However, the formation efficiency of polymer/SiO 2 NCPs could not be improved with further increase of the sonication power.