SIMS analysis of conducting polypyrrole–silica gel composites

Secondary ion mass spectrometry (SIMS) has been used to characterize novel hybrid conducting polypyrrole–silica gel composites. The silica gel particles act as a high surface inorganic substrate for the in situ chemical synthesis of polypyrrole (PPy) in aqueous media. However, the conventional method using untreated silica gel as a host material for pyrrole polymerisation led to insulating PPy–silica composites, which exhibit a silica-rich surface. By contrast, pre-treatment of the silica gel particles by aminopropyltriethoxysilane (APS) prior to polymerisation results in conducting PPy–APS–silica composites, the surface of which was found to be PPy-rich. The present study uses the unique capabilities of SIMS to distinguish unambiguously between fragments from the silane coupling agent and the conducting PPy overlayers. Specific negative ions from PPy and the underlying substrate particles were effective in monitoring the change in the PPy content at the surface of the composites vs. the initial concentration of APS used to pre-treat silica gel particles. This SIMS analysis clearly demonstrated that APS is effective in increasing the surface PPy content and thus confirms previously published XPS data based on some necessary assumptions.