Cyclic temperature dependence of electrical conductivity in polyanilines as a function of the dopant and synthesis method

Abstract

Four Polyanilines (PANI) doped with different acids (HCl, dodecylbenzene sulfonic acid or DBSA and sodio-5-sulfoisophtalic acid or NaSIPA) have been prepared by chemical oxidative polymerization, through direct and indirect routes of synthesis. The synthesis conditions have been optimized to be simple, low-cost and transferable to industrial processing. The PANIs have been characterized by Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and electrical DC conductivity. The nature of the acid dopant and synthetic conditions affect the doping level, oxidation state, presence of oligomeric chains and morphology, which account for the conductivity values spanning from 3.9 to 14.7 S/cm. The polymers were subjected to different heating ramps and heating-cooling cycles to test the dependence of electrical conductivity with temperature. Conductivity retention upon heating is affected by moisture content, thermal stability of the dopant, strength of the PANI-acid complex and rearrangement capability of both PANI and organic dopant alkyl chains. Two DBSA doped PANIs, obtained by direct and indirect methods, exhibit the best conductivity retention up to 150 ºC and excellent thermo-resistive properties in cyclic experiments, which make them potential materials for thermal sensor applications.