Voltammetric and waveguide spectroelectrochemical characterization of ultrathin poly(aniline)/poly(acrylic acid) films self-assembled on indium-tin oxide

We report on the spectroelectrochemical characterization of conducting polymer (CP) films, composed of alternating layers of poly(aniline) (PANI) and poly(acrylic acid) (PAA), deposited on ITO-coated, planar glass substrates using layer-by-layer self-assembly. Absorbance changes associated with voltammetrically induced redox changes in ultrathin films composed of only two bilayers (ITO/PANI/PAA/PANI/PAA) were monitored in real time using a unique multiple reflection, broadband attenuated total reflection (ATR) spectrometer. CP films in contact with pH 7 buffer undergo a single oxidation/reduction process, with ca. 12.5% of the aniline centers in the film being oxidized and reduced. The ATR spectra indicate that during an anodic sweep, the leucoemeraldine form of PANI in these films is oxidized to generate both the emeraldine and pernigraniline forms simultaneously. A comparison of the behavior observed during anodic and cathodic sweeps suggests that the rate of oxidation is limited by structural changes in the polymer film originating in electrostatic repulsion between positively charged PANI chains.