Angular Dependence of Raman Spectra for Electroactive Polymer Films on a Platinum Electrode

The redox transformations in a conducting polymer film on a platinum electrode were studied by Raman spectroelectrochemistry at fixed potentials depending on the incidence angle of the laser beam. Raman scattering was excited with a laser at a wavelength of 532 nm. Polyaniline (PANI) and its complex with poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPSA) were used as a conducting polymer. The polymer films were deposited by potentiostatic electropolymerization. By varying the incidence angle of the beam it is possible to obtain a Raman spectrum without the bands of the substrate overlapping with the characteristic bands of the polymer to minimize the substrate effect on the interpretation of the results. A comparative study of the electrochemical oxidation/reduction of the PANI films taking into account the detected angular dependence showed that, unlike the PANI films obtained in the presence of hydrochloric acid, the films of the PANI-PAMPSA complex retained the radical cation state of PANI in the range of the cathodic potentials. The reason for this is the presence of a nonconductive polymer acid phase in the PANI-PAMPSA film, as a result of which the percolation threshold of the conducting domains of PANI appears at less cathodic potentials, hindering further extraction of the positive charge during the film reduction. In addition, the use of this approach can significantly improve the accuracy of determination of the threshold potential of the leucoemeraldine-emeraldine transition.