Redox properties of polypyrrole bilayers

Abstract

The spatially separated bilayers of polypyrrole (PPy) doped with anions of limited (dodecylsulfate (DDS) and sulfate) and good mobility (chloride) have been prepared by consecutive electrodeposition. The perfect coverage of PPy in the inner layer was obtained already at a very low effective thickness (<0.05 μm) of the outer layer. The peculiarity of the redox behavior of PPy bilayers has been investigated by cyclic voltammetry (CV) and electron probe microanalysis (EPMA). Ion transport through the outer PPy film has been characterized. The cation permeability in the mainly reduced outer component of PPy/DDS/Cl bilayer is limited and increases in the sequence of decreasing hydrated ion radii. The transport of the chloride dopant ions in the course of the reduction process of the inner layer of PPy/Cl/DDS and PPy/Cl/SO 4 bilayers through the hydrophobic PPy/DDS and even through the dense but less hydrophobic PPy/SO 4 film proceeds relatively easily. The penetration of the anions of the test solution during the reoxidation process of the PPy/Cl inner layer through the PPy/DDS outer layer is, on the contrary, essentially hindered. The reason for the high resistance to ion movement is the hydrophobic character of the PPy/DDS outer layer in which the amount of the electrolyte test solution is too low in order to initiate the anion migration process. Ion transport under conditions of simultaneous redox process in the outer and inner layer is characterized.