Comparative studies of the structure, morphology and electrical conductivity of polyaniline weakly doped with chlorocarboxylic acids

We report the results of studies on two series of polyaniline (PANI), doped with dichloroacetic (DCA) and trichloroacetic ( TCA) acids, respectively, at various doping rates and obtained by the in situ polymerization method. Samples were characterized by x-ray diffraction, scanning electron microscopy and conductivity measurements. The direct current ( dc) and alternating current (ac) electrical conductivities of PANI salts have been investigated in the temperature range 100-310 K and frequency range 7-10(6) Hz. The results of this study indicate better chain ordering and higher conductivity for PANI doped with TCA. The dc conductivity of all samples is suitably fitted to Mott's three-dimensional variable-range hopping (VRH) model. Different Mott parameters such as characteristic temperature T-0, density of states at the Fermi level (N(EF)), average hopping energy (W) and the average hopping distance (R) have been evaluated. The dependence of such values on the dopant acid used is discussed. At high frequencies, the ac conductivity follows the power law sigma(ac)(omega,T) = A(T)omega(s)(T,(omega)), which is characteristic for charge transport in disordered materials by hopping or tunnelling processes. The observed increase in the frequency exponent s with temperature suggests that the small-polaron tunnelling model best describes the dominant ac conduction mechanism. A direct correlation between conductivity, structure and morphology was obtained in our systems.