Growth of Electropolymerized Polyaniline Thin Films

Electroactive polyaniline films were grown by potentiodynamic electropolymerization at planar gold electrodes from deaerated solutions of aniline (1.0 M) in aqueous HCl (2.0 M). Films were produced by repeated cycling over the range −0.20 to +0.65 V vs SCE to six different levels of electropolymerization charge density. At each level, the separate films were analyzed by cyclic voltammetry at a 50 mV/s scan rate in deaerated 0.2 M HCl at 20 °C, by ex situ spectroscopic ellipsometry over the range 1.5–4.0 eV at an incidence angle of 70°and by Rutherford backscattering spectroscopy (RBS) using a ⁴He ion beam with an energy of about 1.8 MeV. The anodic charge density measured at 50 mV/s over the range −0.20 to +0.80V vs SCE varied from 8.6 × 10⁻⁴ to 1.2 × 10⁻² C/cm². Measured film thicknesses, determined by spectroscopic ellipsometry, varied from 100 to 1600 Å. The anodic charge density was found to correlate linearly with film thickness over this range, consistent with surface confined electroactivity. The molar concentration of oxidizable equivalents in the polymer film is a remarkably constant 4.3 × 10⁻³ M equiv/cm³ over the thickness range studied. RBS analysis of the polymer film indicates that within the limit of the depth resolution of the RBS instrument the Cl species are evenly distributed throughout the thickness of the film and that these species include both polymer cation associated chloride ion and trapped HCl.