Photoinduced and thermal-activated doping of polyaniline

Abstract

The reaction of 50% oxidized polyaniline (emeraldine base, EB) with alkyl halide and viologen in the dry state was studied using X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, and sheet resistance measurements. To facilitate this study, a low-density polyethylene substrate was first surface graft copolymerized with vinylbenzyl chloride or viologen moieties. A coating of polyaniline (PANI) was then deposited on the top of the film. Under UV irradiation or heat treatment at 65 °C or higher, the PANI reacted with the vinylbenzyl chloride and/or viologen, resulting in its conversion from the insulating base state to the conducting state. The conversion was more readily achieved with viologen, and a significant portion of the imine nitrogen of PANI was converted to positively charged nitrogen. The photoinduced method was more effective than the thermal-activated process in achieving a conducting PANI film. The most conductive film was obtained by irradiating the PANI-viologen film for 30 min or more using a 1 kW Hg lamp, and the conductivity achievable was about 1 order of magnitude lower than that of the conventional acid-protonated PANI film.