Environmental stability of electrically conductive viologen-polyaniline systems

Viologen-polyaniline (PANI) systems were prepared by PANI being coated onto viologen-grafted low-density polyethylene films. PANI in this system could undergo photoinduced doping with ultraviolet irradiation. The electrical stability of the electrically conductive viologen-PANI systems was found to be stable in air, but the conductivity decreased rapidly when the sample was treated in aqueous media of pH > 5 because of the migration of the anions out of PANI into water. However, the conductivity increased by a factor of 2 after treatment in a 1M HCl solution because of the further protonation of PANI by acid. The structural changes of these systems were monitored with ultra violet-visible absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and resistance measurements. The electrical stability of the viologen-PANI system in water could be enhanced via spin coating with poly(methyl methacrylate) (PMMA) because this layer inhibited the migration of the anions out of the system. The photoinduced doping of PANI could be carried out either before or after the spin coating of PMMA. The advantages and limitations of each method were demonstrated. A PMMA coating with a thickness of approximately 10 mum allowed a significant doping level to be achieved within a short period of irradiation and, at the same time, effectively shielded the film from the effects of the aqueous medium. (C) 2002 Wiley Periodicals, Inc.