Effect of synthesis parameters on the particle size, composition and colloid stability of polypyrrole-silica nanocomposite particles

The effect of varying the oxidant, monomer and silica sol concentrations, silica sol diameter, polymerization temperature, stirring rate and oxidant type, on the particle size, polypyrrole content and conductivity of the resulting polypyrrole-silica colloidal nanocomposites has been studied. Surprisingly, nanocomposite formation appears to be relatively insensitive to most of the above synthesis parameters. One synthesis parameter which does have a significant and reproducible effect is the stirring rate: smaller, more monodisperse nanocomposite particles are obtained from rapidly stirred reaction solutions. However, this effect is only observed for the (NH4)(2)S2O8 oxidant. An alternative oxidant, H2O2/Fe3+, was found to give nanocomposites of similar particle size, polypyrrole content and conductivity to those obtained using the (NH4)(2)S2O8 oxidant. The colloid stability of these polypyrrole-silica nanocomposite particles depends on their silica content. The colloid stability of a silica-rich nanocomposite prepared using the (NH4)(2)S2O8 oxidant in the presence of electrolyte was comparable to that of a silica sol, whereas a polypyrrole-rich nanocomposite prepared using FeCl3 had markedly poorer colloid stability under these conditions. These observations are consistent with a charge stabilization mechanism for these nanocomposite particles.