Light reflection at polyaniline films and its application to a kinetic study of polymer chain conformation

Light reflection at polymer-coated electrodes is studied for polyaniline, poly(o-methylaniline), and poly(o-methoxyaniline). Reflected light intensity is found to be affected greatly by the applied potential for the two reasons: one is absorption of light due to coloring of the oxidized polymer film and the other is light scattering which is concerned with a polymer chain conformation upon oxidation. A new method based on the potential dependence of light reflection is proposed for studying kinetics of conformational changes of polymer chains. The rate constants evaluated are in the range of 0.05-8 s⁻¹ at room temperature, depending on the sort of polymers, the film thickness, and pH of the solution. Irrespective of the sort of polymers, the increase in film thickness or solution pH leads to the decrease of the rate constant. It is found that a film morphology has a significant effect on the rate constant, as confirmed by a comparison of rate constants observed with polyaniline films grown at different rates.