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

Abstract

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), SiO2 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 SiO2 and SDS content. The results indicate that the number fraction of polymer/SiO2 NCPs (fNCP) in the latex particles was below 4%, and that plain polymer particles dominated in all of the emulsions regardless of the SiO2 and SDS content when the sonication power was 95W. 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/SiO2 NCPs, and a very small amount of sub-micrometer polymer/SiO2 aggregates. These particles evolved from small plain monomer droplets, medium monomer droplets containing SiO2 NPs, and micrometer monomer droplets containing many SiO2 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 SiO2 NPs among monomer droplets. The fNCP value markedly increased to ∼39% upon increase of the sonication power to 190W. However, the formation efficiency of polymer/SiO2 NCPs could not be improved with further increase of the sonication power.