Efficient preparation of polystyrene/silica colloidal nanocomposite particles by emulsion polymerization using a glycerol-functionalized silica sol.

Colloidally stable polystyrene/silica nanocomposite particles of around 200-400 nm diameter and containing 22-28 wt % silica can be readily prepared by aqueous emulsion polymerization at 60 degrees C using a cationic azo initiator in combination with a commercially available glycerol-functionalized ultrafine aqueous silica sol in the absence of any surfactant, auxiliary comonomer, or nonaqueous cosolvent. Optimization of the initial silica sol concentration allows relatively high silica aggregation efficiencies (up to 95%) to be achieved. Control experiments confirm the importance of selecting a cationic initiator, since nanocomposite particles were not formed when using an anionic persulfate initiator. Similarly, the glycerol groups on the silica sol surface were also shown to be essential for successful nanocomposite particle formation: use of an unfunctionalized ultrafine silica sol in control experiments invariably led to polystyrene latex coexisting with the silica nanoparticles, rather than efficient nanocomposite formation. Electron spectroscopy imaging transmission electron microscopy studies of ultramicrotomed polystyrene/silica nanocomposite particles indicate well-defined "core-shell" particle morphologies, which is consistent with both X-ray photoelectron spectroscopy and aqueous electrophoresis studies.