The role of a silane coupling agent in the synthesis of hybrid polypyrrole–silica gel conducting particles

Abstract

The preparation of new hybrid conducting polymer–silica gel particles is described. The silica gel acts as a high surface area substrate (431 m² g^–1) for the in situchemical synthesis of conducting polypyrrole in aqueous solution in order to obtain hybrid polypyrrole–silica particles. The role of a common silane coupling agent (i.e. aminopropyltriethoxysilane, APS) in the pretreatment of silica gel prior to polymerization and preparation of polypyrrole–APS–silica particles is also investigated. It was found by TGA that the polypyrrole mass loading is higher in polypyrrole–APS–silica than in polypyrrole–silica particles. XPS results indicated that APS-treated silica leads to polypyrrole-rich surface particles not found with the untreated silica. Consequently, the polypyrrole–APS–silica pellets were three orders of magnitude more conductive than those of polypyrrole–silica.The surface area of the polypyrrole–silica (422 m² g^–1), as measured by BET, matched that of the untreated silica whilst that of the polypyrrole–APS–silica (162–184 m² g^–1) is significantly lower. The combination of XPS, TGA, BET and conductivity measurements suggest that pyrrole is predominantly polymerized in the pores of the untreated silica gel whilst the APS pretreatment of silica leads to the formation of a thin overlayer of polypyrrole at the surface of the silica gel in addition to a higher conducting polymer loading in the gel pores.