EVOLUTION OF THE CONDUCTING STATE OF POLYANILINE FROM LOCALIZED TO MESOSCOPIC METALLIC TO INTRINSIC METALLIC REGIMES

The results of microwave dielectric constant (epsilon(mw)) and dc conductivity (sigma(dc)) of doped polyaniline (PAN) samples in different charge delocalization regimes are reported. With camphor sulfonic acid doped PAN prepared in m-cresol solvent (PAN-CSA (m-cresol)) representing the most delocalized material, a negative epsilon(mw) is measured indicating an intrinsic metallic state. The Drude model at low frequency is used to estimate a relatively small plasma, frequency w(p) similar or equal to 0.015 eV and an anomalously long scattering time tau similar or equal to 1.2x10(-11) a. This tau implies the importance of phonon back scattering for the most delocalized electrons as expected for the open Fermi surface of a highly anisotropic metal. Depending on the crystallinity, there are two different charge localization regimes in PAN samples: uncoupled metallic islands and coupled ''mesoscopic'' metallic state. The three-dimensional nature of metallic state is demonstrated by the correlation of low temperature dielectric response with the parallel and perpendicular crystalline domain lengths obtained from x-ray data. The charge localization to delocalization transition dependence on the polymer processing will be discussed. We present the temperature dependent nonmetal-metal transition for some preparations of PAN-CSA (m-cresol). The intrinsic conductivity of metallic PAN is estimated to be similar to 10(7) S/cm.