The effect of polymerization potential and electrolyte type on conductive polymer coatings

Pure conductive films were prepared by the anodic polymerization of pyrrole in aqueous solutions by applying a potential in the range of 0.6 to 2.0 V. Conductive composites were prepared using a two step process: microemulsion polymerization to form a porous (nonconductive) coating followed by electropolymerization of pyrrole. The porous nonconductive coating was prepared by polymerizing a microemulsion containing acrylamide and styrene as monomers and a surfactant: anionic, sodium dodecylsulfate; cationic, hexadecyltrimethylammonium bromide; and zwitterionic, octadecyldimethyl betaine. The minimum applied potential required for electropolymerization is dependent on solvent type and when there is a copolymer coating, also the surfactant in the coating and the swellability of the coating in the solvent. The chronoamperometric response of pyrrole electropolymerization is dependent on the polymerization potential and not on the counter ion. The electrochemical behavior is extremely sensitive to the chemical composition of polypyrrole which could not be verified using FTIR. The incorporation of different counter ions into the polypyrrole matrix was studied using both cyclic voltammetry and electron microscopy. Electrochemical studies relating the peak current to the charge passed during electropolymerization by a power-law relationship gives insight into the complexity of the polypyrrole switching reaction.; The switching reaction of conductive polymers can be described by two simultaneous processes: electron transfer to and from the conductive polymer and ion diffusion to maintain charge neutrality. The charge transfer controlled switching reaction has been modeled as a first order irreversible reaction. The model requires a number of polymer related parameters: electron transfer numbers, kinetic constants, switching potential and degree of anion incorporation. The electron transfer numbers and kinetic constants are calculated from the peak currents and the peak positions, respectively. The model predicts the linear dependence of both the peak current to charge passed during electropolymerization and scan rate in cyclic voltammetry and the charge passed during the switching reaction to charge passed during electropolymerization and time in chronocoulometry.