Electrodepositing of polypyrrole films on walls of thin-layer cells

In recent years numerous approaches have been applied by researchers on a worldwide basis to obtain polypyrrole (PPy) with high conductivity and good mechanical properties through improved chain alignment. Examples of some innovative approaches include stretch orientation of PPy films/sup 1/, electrodeposition of films under shear flow conditions/sup 2/, deposition within the pores of nanoporous membranes/sup 3/ and molecular sieve solids/sup 4/ and electropolymerisation at liquid/liquid/sup 5/ or liquid/air/sup 6/ interfaces. Our experiments utilise a novel technique/sup 7/ in which polymerisation occurs at non-conducting surface at a liquid/solid interface in a thin-layer cell (TLC). A schematic description of a TLC is illustrated in Figure 1. In the initial set of experiments the upper and lower layers in such cells consisted of poly (methyl methacrylate) (PMMA) and glass, respectively. Epoxy adhesive was used to bond the glass and plastic to the metallic anode. In a typical experiment pyrrole (0.6M) and sodium p-toluenesulfonate (0.5M) aqueous solutions were placed in a thermostated container in which a TLC was also placed. Polymerisation was conducted potentiostatically at 0.80V (vs SCE) in TLC with gap width of 760 microns at 25/spl deg/C. PPy film, formed after 20 minutes, was removed from the cell stripped of residual reactants by Soxhlet extraction in a 1:1 acetonitrile/water mixture, then dried in a vacuum oven at 60/sup /C. Scanning electron microscopy (SEM) examination of the PMMA facing surface of the film revealed rippled surface markings, which bear resemblance to those formed on indium-tin oxide glass electrodes/sup 8, 9, 10/ and on a metallic electrode/sup 11/ reported recently. A cross section of an edge of these films formed in the TLC displayed a honeycomb structure. On the basis of the these photographs, others obtained with better resolution with a field emission scanning electron microscope and photographs of the PMMA surface prior to its cov- rage by PPy by atomic force microscopy, a reasonable hypothesis for the mechanism of formation of these films is proposed.