Transport studies of emeraldine salts protonated by phosphoric acids

Abstract

Electrical transport properties of polyaniline prepared by chemical oxidative polymerization in the presence of phosphoric acid were investigated by low temperature conductivity and thermoelectric power measurements. As the ratio of acid to aniline is optimized (Z = 6) at the stage of polymerization, the freshly prepared emeraldine salt form of the polyaniline shows (i) relatively high electrical conductivity, σ ~ 40 S/cm at room temperature, (ii) temperature dependence of the conductivity characteristic of the variable range hopping (VRH), In σ ∝ — ( T 0/ T) x , with exponent x = 1/3, and (iii) linear temperature dependence of the thermoelectric power. As the molar ratio Z decreases from 6 to 1, the VRH exponent x systematically changes from 1/3 to 1/2 and the thermoelectric power decreases from + 7.6 to + 0.2 μV/ K. The systematic variation of the transport parameters obtained from the temperature dependence was attributed to combined contributions from the metallic transport and VRH process in the disordered polymeric system.