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

Abstract

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 H 2SO 4 as electrolyte. Effect of dopant in presence of electrolyte is rarely studied in the field of conducting polymers. Various inorganic salts as dopants, viz. K 2SO 4, Na 2SO 4, Li 2SO 4, MgSO 4, KCl, NaCl, LiCl and MgCl 2 are used at room temperature. The films were electropolymerized in solution containing 0.1 M monomer, 1 M H 2SO 4 as electrolyte and 1 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, K 2SO 4 is found to be the best in sulphate category and KCl in chloride category.