Colloidal dispersions of polymer-silica nanocomposite particles were synthesized in high yield by homopolymerizing 4-vinylpyridine (4VP) in the presence of an ultrafine silica sol using a free-radical initiator in aqueous media at 60°C. Copolymerization of 4VP with methyl methacrylate and styrene also produced colloidally stable nanocomposite particles, in some cases for comonomer feeds containing as little as 6 mol % 4VP. However, homopolymerization of styrene or methyl methacrylate in the presence of the silica sol did not produce nanocomposite particles in control experiments. Thus a strong acid-base interaction between the silica sol and the (co)polymer appears to be essential for nanocomposite formation. Transmission electron microscopy studies confirmed the presence of the ultrafine silica sols within the nanocomposite particles, which typically exhibited "currant-bun" particle morphologies. This is in contrast to the "raspberry" particle morphologies previously reported for conducting polymer-silica nanocomposite particles. The average silica contents and mean particle diameters of the vinyl (co)polymer-silica nanocomposites were surprisingly insensitive to the synthesis conditions, as judged by thermogravimetric analysis and disk centrifuge photosedimentometry studies, respectively. The latter technique also indicated that some of the copolymer-silica dispersions were appreciably flocculated, although the degree of dispersion could be improved by redispersion in alkaline media. 1 H NMR spectroscopy studies on the extracted nanocomposites confirmed incorporation of the 4VP comonomer, with reasonable agreement between copolymer compositions and comonomer feeds being obtained. Aqueous electrophoresis measurements confirmed that the surface of the 4VP-silica particles is polymer-rich, which is consistent with their currant-bun morphology. Timeresolved photon correlation spectroscopy studies during nanocomposite formation showed that particle growth occurred rapidly, with particles reaching their final size after approximately 1 h. Doubling the 4VP monomer concentration at a fixed 4VP/silica ratio led to an increase in particle size from 150 to 220 nm. IntroductionIn polymer nanocomposites the polymer chains are confined to nanoscale (1-10 nm) dimensions. Following pioneering work by Giannelis and co-workers, 1,2 it is now recognized that these materials can exhibit unusual, even unique, properties 3 which cannot be obtained simply by comixing the polymeric component with the inorganic phase. 4,5 In many literature reports polymer nanocomposites are synthesized by creating or modifying the inorganic phase in the presence of preformed polymer chains. For example, Messersmith and Stupp 6 prepared calcium aluminate in the presence of various water-soluble polymers and obtained "organoceramic" materials. In contrast, Mark and co-workers 7 prepared monolithic poly(methyl acrylate)/SiO 2 nanocomposites by dispersing surface-modified silica particles in methyl acrylate, followed by polymerization of the monomeric con...

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Aniline was polymerized in the presence of ultrafine colloidal silica particles (hydrodynamic diameter 35 nm) in aqueous media and, given a sufficient silica concentration, colloidally stable polyaniline−silica particles were obtained. The particle size of the resulting dispersions was determined by both dynamic light scattering and disk centrifuge photosedimentometry. The typical size of these polyaniline−silica particles is in the range 300−600 nm and is insensitive to the concentration of components in the reaction mixture, temperature, or acidity of the reaction mixture. Particles produced at 0 °C are spherical and their shape becomes less defined when polymerization proceeds at 25 °C. As the silica size is increased, the composite particles become larger and their raspberry morphology more distinct. The electrical conductivity of a typical polyaniline (37.8 wt%)−silica composite is 6.1 × 10-2 S cm-1 at 25 °C. It grows with increasing temperature and does not depend on the frequency in the investigated range from 20 Hz to 1 MHz.

Poly(N-vinylpyrrolidone)-stabilized polystyrene (PS) latexes have been coated with thin overlayers of polyaniline (PANi) to produce electrically conductive “core−shell” particles. In this work we focused on the morphology of the PANi overlayer, the colloid stability of the coated latexes, and electrical conductivity. PANi-coated particles exhibit a nonuniform morphology as observed by scanning electron microscopy (SEM), in comparison with the relatively smooth polypyrrole overlayers synthesized in a previous study (Lascelles, S. F. et al., J. Mater. Chem. 1997, 7, 1339 and 1349). Disk centrifuge photosedimentometry confirmed that the PANi-coated PS latexes were weakly flocculated. The underlying PS latex “core” was quantitatively removed by solvent extraction, and SEM observations of the PANi residues revealed a “broken egg shell” morphology. Vibrational bands due to the PANi component were more intense in both the FT-IR and Raman spectra of the PANi-coated PS latexes, which is also consistent with the “core−shell” morphology. No reduction in the surface roughness of the PANi overlayer was observed when the rate of the aniline polymerization was decreased or if the latex surface was pretreated with either a thin polypyrrole overlayer or a layer of adsorbed surfactant. Similarly, only rough PANi overlayers were observed when coating a sulfonated PS latex. However, a more uniform deposition of PANi and a corresponding improvement of colloid stability were obtained using aniline hydrochloride monomer in the absence of added acid.