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 concentratio ns, silica sol diameter, polymerization temperature, stirring rate and oxidant type, on the particle size, polypyrrole content and conductiv ity of the resulting polypyrrole-silica colloidal nanocomposites has b een studied. Surprisingly, nanocomposite formation appears to be relat ively insensitive to most of the above synthesis parameters. One synth esis parameter which does have a significant and reproducible effect i s the stirring rate: smaller, more monodisperse nanocomposite particle s are obtained from rapidly stirred reaction solutions. However, this effect is only observed for the (NH4)(2)S2O8 oxidant. An alternative o xidant, H2O2/Fe3+, was found to give nanocomposites of similar particl e size, polypyrrole content and conductivity to those obtained using t he (NH4)(2)S2O8 oxidant. The colloid stability of these polypyrrole-si lica nanocomposite particles depends on their silica content. The coll oid stability of a silica-rich nanocomposite prepared using the (NH4)( 2)S2O8 oxidant in the presence of electrolyte was comparable to that o f a silica sol, whereas a polypyrrole-rich nanocomposite prepared usin g FeCl3 had markedly poorer colloid stability under these conditions. These observations are consistent with a charge stabilization mechanis m for these nanocomposite particles.