Preparation and characterisation of novel polypyrrole–silica colloidal nanocomposites

Abstract

We describe the preparation and characterisation of colloidal dispersions of polypyrrole–silica nanocomposite particles. These nanocomposites have been characterised in terms of their particle size and chemical composition by a wide range of experimental techniques, including transmission electron microscopy, disc centrifuge photosedimentometry, photon correlation spectroscopy, elemental microanalyses, thermogravimetry, infrared spectroscopy and dc solid-state conductivity measurements. We find that both the particle size and the chemical composition depend markedly on the type of chemical oxidant selected for the in situ polymerisation of the pyrrole monomer. For example, using the FeCl₃ oxidant we obtain polypyrrole–silica particles which contain up to 70 m/m% polypyrrole and have particle diameters in the range 160–320 nm, whereas the (NH₄)₂S₂O₈ oxidant yields composite particles which contain only 37–55 m/m% polypyrrole and are ca. 110–180 nm in diameter. In most cases the particle size distributions are reasonably narrow, with standard deviations as low as 13% as measured by disc centrifuge photosedimentometry. We have also investigated the mechanism of formation of these nanocomposite particles by studying: (i) the adsorption of pyrrole monomer from aqueous solution onto colloidal silica; (ii) the adsorption of oxidant [either FeCl₃ or (NH₄)₂S₂O₈] from aqueous solution onto colloidal silica. These adsorption studies indicate that either the monomer or the oxidant is partially adsorbed onto the silica particles prior to polymerisation in all of our syntheses. Thus, surface polymerisation processes may be important in the formation of these nanocomposite particles.