The interactions between viologens and polyaniline of different intrinsic oxidation states in the solid state, under photo-irradiation, were investigated. These interactions were facilitated by depositing a thin coating of polyaniline onto low-density polyethylene films, which have been surface grafted with viologen. The films were characterized by X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy and sheet resistance measurements. The polyaniline coatings were observed to change from the insulating state to the conducting state upon near-UV irradiation. The reaction of the fully reduced form of polyaniline (leucoemeraldine) with viologen is dependent on the presence of oxygen. It is proposed that the conversion of the polyaniline to the conductive state occurs through a protonic acid doping mechanism whereby hydrochloric acid is formed during the ring-opening reaction of viologens with amine nitrogen of the polyaniline upon irradiation of the films. The adhesion of PANI to the viologen-grafted film as assessed by peel tests is good and the stability studies indicated that the conductivity of the photo-irradiated films is stable in air. However, the films undergo rapid dedoping in water, resulting in a loss of conductivity.
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