Effect of inorganic dopants (in presence of electrolyte) on the conductivity of polyaniline, poly(o-toluidine) and their copolymer thin films

An attempt has been made to prepare polyaniline (PA), poly(o-toluidine) (POT) and copolymer (PA-POT) thin films doped by several inorganic salts (sulphates and chlorides) with varying size of cation using aqueous solution of H2SO4 as electrolyte. Effect of dopant in presence of electrolyte is rarely studied in the field of conducting polymers. Various inorganic salts as dopants, viz. K2SO4, Na2SO4, Li2SO4, MgSO4, KCl, NaCl, LiCl and MgCl2 are used at room temperature. The films were electropolymerized in solution containing 0.1 M monomer, 1 M H2SO4 as electrolyte and I M inorganic salt by applying sequential linear potential scan rate 50 mV/s between -0.2 and 1.0 V versus Ag/AgCl electrode. The electrosynthesized films were characterized by cyclic voltammetry, UV-visible spectroscopy and conductivity measurements using four-probe technique. It was observed that the UV-visible peaks are appearing at about 800-810 nm with a shoulder at 410-420 nm for emeraldine salt (ES) phase of PA, POT and PA-POT without any doping salt. In the presence of salts, a shift for these absorption spectra is observed to lower wavelength in 760-800 nm, however, a shift of shoulder is to higher wavelength in 435-445 nm. In the overall study, an increase in conductivity is observed for all above-mentioned dopants, and among these, K2SO4 is found to be the best in sulphate category and KCl in chloride category. (C) 2002 Elsevier Science B.V. All rights reserved.