Influence of the electrostatic interactions in a Pickering emulsion polymerization for the synthesis of silica-polystyrene hybrid nanoparticles

Hypothesis: Silica-polystyrene hybrid nanoparticles were synthesized by Pickering emulsion polymerization. The coupling effect of initiator type and silica surface charge was studied to exhibit the predominant role of electrostatic interactions in the synthesis mechanisms. Experiments: Non-ionic hydrophobic initiator (2,2'-azobis(2-methylpropionitrile), AIBN) or anionic hydrophilic initiator (sodium persulfate, NaPS), and positively or negatively charged silica were used as reactants with styrene for Pickering emulsion polymerization. Their interactions were evaluated by Zeta potential measurements. The droplet size and the stability of the Pickering emulsions, and the hybrid particle morphology, surface coverage, size and agglomeration were evaluated by laser granulometry and microscopy. Findings: Similar surface charge between negatively charged silica particles and an anionic initiator led to strong repulsions and thus to non-covered polystyrene nanoparticles. With positively charged silica, a high decoration was obtained due to attractive interactions between the inorganic and the organic phases, but a strong agglomeration was also observed. The use of a non-ionic initiator led to a homogeneous coverage with negatively charged silica. With positively charged silica micronic sizes were formed by following two different mechanisms. These data, by enriching the existing literature, led to a more complete and robust description of the emulsion polymerization synthesis for hybrid nanostructures, (C) 2015 Elsevier Inc. All rights reserved.