BACKGROUND: The application potential of conducting polymers depends on their conductivity. It is generally assumed that the conductivity determined in the dry state is a parameter that unambiguously characterizes them.RESULTS: The conductivity of polyaniline (PANI) films immersed in aqueous solutions of sulfuric acid may be more than 1000 times higher compared with that obtained by measurement of dry films in air, and is estimated to reach a value exceeding 3300 S cm−1 in 1 mol L−1 sulfuric acid. This is explained by the reduction of conductivity barriers between conducting PANI islands.CONCLUSION: The organized polymer chains in the conducting islands of a PANI film are separated by disordered regions of low conductivity in the dry state. The penetration of sulfuric acid solution into the disordered areas increases the overall conductivity of the PANI film by improving the electrical contact between the islands through ionic charge transport. The electronic conductivity of the PANI film in the dry state thus converts to mixed electron–proton conduction in acidic aqueous solutions, electron conductivity being dominant in ordered regions and ionic conductivity in disordered regions separating them. Weakly bound protons are the most important ionic charge carriers hopping along the PANI chains. Copyright © 2009 Society of Chemical Industry

The acid doping process of the mixtures of N,N'-diphenyl-1,4-phenylenediamine (DPPD) and N,N'-diphenyl-1,4-quinonediimine (DPQD), reduced and oxidized phenyl-capped aniline dimers respectively, has been studied in detail by UV-vis-NIR and ESR spectroscopies. The addition of the acid to the mixtures of DPPD and DPQD leads to the formation of one type of radicals by intermolecular interactions. Full conversion of the aniline dimer molecules to the radical form is achievable only in stoichiometric mixtures of DPPD and DPQD. Concentration of radical species may change over time according to processes involving hydrolysis. The mechanisms of the acid doping of the phenyl-capped dimer process and subsequent side processes are proposed.

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