Effective Charge Trapping in Bilayers of Conducting Polymers Based on Polypyrrole and Poly(N-methylpyrrole)

Bilayers of conducting polymers composed of polypyrrole doped with poly(4-styrenesulfonate) [PPy(PSS)] or dodecylsulfate ions [PPy(DS)] and poly(N-methylpyrrole) (PMPy) or polypyrrole (PPy) doped with perchlorate ions were studied using voltammetric, chronoamperometric and EDAX methods. The polymers were used in the following sequence (inner layer/outer layer): PPy(PSS)/PPy, PMPy/PPy(DS) and PPy(DS)/PMPy. Charge trapping effects were studied by comparing redox charges of bilayers and single polymeric layers. For PPy(PSS)/PPy bilayers a very effective trapping of the inner layer in the oxidized state was found in solutions of BaCl2, because Ba2+ ions, which are necessary to reduce the inner layer, could not penetrate the outer PPy film. For bilayers PPy(DS)/PMPy and PMPy/PPy(DS) the charge of the inner layer was also found to be almost completely trapped, i.e., these layers are in the oxidized state, independent of the potential applied. This effect results from limited permeability of PPy(DS) for ions, due to the presence of surface active dodecylsulfate ions, inhibiting penetration of PPy(DS) by ions and moreover from low permeability of PMPy for cations needed to reduce PPy(DS) in PPy(DS)/PMPy bilayers.