SURFACE CHARACTERIZATION OF CONDUCTING POLYMER-SILICA NANOCOMPOSITES BY X-RAY PHOTOELECTRON-SPECTROSCOPY

The surface characterization of a range of conducting polymer-silica colloidal nanocomposites by X-ray photoelectron spectroscopy (XPS) is described. The silicon atoms in the silica component and the nitrogen atoms in the conducting polymer (polypyrrole or polyaniline) component have-been utilized as unique elemental ''markers''. Thus, measurement of the silicon/nitrogen atomic ratio by XPS allows a semiquantitative assessment of the silica/conducting polymer surface composition of: the nanocomposite particles. These surface atomic ratios were then compared with the bulk silicon/nitrogen atomic ratios calculated for the nanocomposites from our macroscopic chemical composition data. We were able to confirm that, for all samples investigated, the surface composition of the conducting polymer-silica particles is silica-rich with respect to their bulk composition. These observations are consistent with the observed long-term colloidal Stability of these dispersions. Furthermore, the surface composition of the polypyrrole-silica silica nanocomposites was correlated with the colloid stability of these dispersions in pH 3 and 9 buffer solutions. Finally, our XPS data confirm that, although somewhat depleted from the-surface of the particles, the conducting polymer component is nevertheless present. This observation is consistent with the relatively high solid state electrical conductivities obtained for compressed pellets of these materials.