Effect of dopants on electron localization length in polyaniline

The electronic behavior of chemically synthesized polyaniline depends on the amount of disorder-whether homogeneous or inhomogeneous-created during synthesis and doping. Its physical properties are significantly affected by a number of parameters such as catalyst type, solution pH, oxidant/monomer ratio, solvent type, secondary doping, dopant type, dopant size and synthesis temperature. With the view of studying the dependence of electron localization behavior on the dopant type, all other factors remaining the same, we report in this paper a systematic study of NMR, EPR, magnetic susceptibility, and dc conductivity measurements for seven doping acids. The EPR lineshape in all these cases is close to a Lorentzian, but the linewidth is sensitively dependent on the type of the dopant. In spite of differences in the magnitude and the temperature dependences of dc conductivity and magnetic susceptibility data, the experiments reveal a localization length of approximately 30 Angstrom for all the samples. It is concluded that, unlike drastically different charge transport behaviors caused by the presence of substituent groups on phenyl rings of the polymer chains, dopant molecules belonging to a given family have virtually no effect on the electron localization length. (C) 2003 Published by Elsevier Science B.V.