Redox properties of polypyrrole bilayers

The spatially separated bilayers of polypyrrole (PPy) doped with anions of limited (dodecylsulfate (DDS) and sulfate) and good mobility (chloride) hav e been prepared by consecutive electrodeposition. The perfect coverage of P Py in the inner layer was obtained already at a very low effective thicknes s (< 0.05 mum) 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 b een characterized. The cation permeability in the mainly reduced outer comp onent of PPy/DDS/Cl bilayer is limited and increases in the sequence of dec reasing hydrated ion radii. The transport of the chloride dopant ions in th e course of the reduction process of the inner layer of PPy/Cl/DDS and PPy/ Cl/SO4 bilayers through the hydrophobic PPy/DDS and even through the dense but less hydrophobic PPy/SO4 film proceeds relatively easily. The penetrati on 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, es sentially hindered. The reason for the high resistance to ion movement is t he 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 mig ration process. Ion transport under conditions of simultaneous redox proces s in the outer and inner layer is characterized. (C) 2001 Elsevier Science Ltd. All rights reserved.