Influence of polymer structure on the electrochemistry of phenothiazine dyes incorporated into Nafion films

Abstract

Electrochemical properties of phenothiazine dyes, thionine (TH⁺) and methylene blue (MB⁺), incorporated into Nafion films have been studied at different acid concentrations. The TH⁺ and MB⁺ dyes adsorbed by Nafion films gave an unusual redox wave at more positive potentials in addition to the usual redox wave at less positive potentials in 0.05 mol dm^–3 H₂SO₄. Upon continuous cycling for 45 min the unusual redox wave disappeared. The two redox waves observed at 0.05 mol dm^–3 H₂SO₄ were accounted for by the distribution of electroactive species in different domains of the Nafion polymer film, i.e. the lower void volume of the interfacial region and the higher void volume of the ionic cluster region. The same dyes incorporated into Nafion films in 0.5 mol dm^–3 H₂SO₄ gave only the usual redox wave, which was accounted for by the molecules residing only in the ionic cluster region of the swelled Nafion film. The same electrochemical behaviour was also observed in Na⁺- and H⁺-Nafion film. The effects of different concentrations of dyes in the Nafion films were also studied in order to understand the influence of the polymer film structure on the electrochemical properties of phenothiazine dyes.