Polystyrene−Silica Colloidal Nanocomposite Particles Prepared by Alcoholic Dispersion Polymerization

Micrometer-sized silica-stabilized polystyrene latex particles and submicrometer-sized polystyrene−silica nanocomposite particles have been prepared by dispersion polymerization of styrene in alcoholic media in the presence of a commercial 13 or 22 nm alcoholic silica sol as the sole stabilizing agent. Micrometer-sized near-monodisperse silica-stabilized polystyrene latexes are obtained when the polymerization is initiated with a nonionic AIBN initiator. These particles are stabilized by silica particles that are present on the latex surface at submonolayer concentration. The total silica content is no greater than 1.1 wt %, which corresponds to a silica sol incorporation efficiency of less than 1.3%. Reduction of the initial silica sol concentration led to a systematic increase in the mean latex diameter. In contrast, submicrometer-sized polystyrene-silica nanocomposite particles are obtained when the polymerization is initiated with a cationic azo initiator. The silica contents of these nanocomposite particles are significantly higher, ranging up to 29 wt %. Zeta potential measurements, XPS, and electron spectroscopy imaging by transmission electron microscopy (ESI/TEM) studies reveal a well-defined core−shell morphology for these particles, whereby the core is polystyrene and the shell comprises the silica sol. After calcination, these nanocomposite particles can form hollow silica capsules. Variation of the initial silica sol and initiator concentration has relatively little effect on the final particle size and silica content of these polystyrene−silica nanocomposite particles, but indicates silica sol incorporation efficiencies up to 72%.