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This study is an attempt to investigate how charge transport in thin redox polymer films spin-coated onto glassy carbon electrode surfaces is affected by the way in which the electroactive group is bound to the polymeric matrix. Two different redox polymers based on methylated and cross-linked poly(4-vinylpyridine) and pentacyanoferrate(II/III) have been synthesized. In the first case, an anionic complex formed by coordinating pyridine to pentacyanoferrate(II) was electrostatically bound to the methylated pyridine groups in the polymer matrix. In the other case, pentacyanoferroate(II) was coordinated directly to unmethylated pyridine groups in the partly methylated polymer film. The film thicknesses were estimated with ellipsometric measurements. Their electrochemical characteristics were investigated using cyclic voltammetry, chronocoulometry and impedance spectroscopy. The apparent charge-transport diffusion coefficient D(app) was almost two orders of magnitude greater in the ion-exchange polymer than in the redox polymer with coordinatively bound electroactive groups. The temperature dependence of D(app) was evaluated using Arrhenius plots.

Ellipsometry has been used to measure the dimensions of quaternized poly(4-vinylpyridine) films containing [Os(bpy)2pvpCl]2+/+ redox groups on glassy carbon electrodes. Film thicknesses and complex refractive indices were deduced using molar absorptivities obtained from photometry or a combination of photometry and cyclic voltammetry. The precision in the film thicknesses was estimated using data obtained from thick and thin films with the same polymer + redox group compositions and from data recorded at 60-degrees and 70-degrees angles of incidence of 633 nm laser light. The effects of errors in the experimentally determined molar absorptivity of the redox groups on film thickness were also assessed. The results of this study suggest that reliable thicknesses can be obtained for both dry and electrolyte-swollen films, and that the presence of light-absorbing redox groups within coatings such as these presents no real obstacle for ellipsometric determinations.

Chronocoulometry and impedance spectroscopy were used to study the dynamics of charge transport in a series of methylated [Os(bpy)(2)(PVP)(x)Cl]Cl polymers (PVP = poly(4-vinylpyridine); bpy = 2,2'-bipyridine; 5 less than or equal to x less than or equal to 40) which were deposited as thin firms on glassy carbon electrodes. Apparent charge propagation diffusion coefficients D-app were of the order of 10(-8) cm(2) s(-1) and were approximately linearly dependent on the total concentration of redox sites but independent of the ratio of oxidized to reduced centres present in a particular coating. Attempts were made to explain these observations in terms of a recent theory of charge transport appropriate for systems in which the redox sites are permanently attached to the polymer chains. It was found that the concentration dependence and magnitude of D-app could be explained satisfactorily by a mean field model of charge propagation.

The activation parameters associated with charge propagation in a series of quaternized poly(4-vinylpyridine) polymers, which contained both electrostatically hound and coordinated redox sites and which were deposited as thin films on electrode surfaces, were derived from the temperature dependence of apparent charge transport diffusion coefficients. The values of the activation energies and entropies obtained are discussed in terms of models of charge transport that are appropriate for redox polymers in which physical displacements of the redox sites are either free or constrained.