Monodispersed redox submicrometer particles created by polyaniline-coated polystyrene latex

A spherical electroactive particle, 65 nm in diameter, was synthesized by coating a sulfonated polystyrene latex particle with the electric conducting polymer (polyaniline). It was suspended in acidic solution, and hence its electrochemical properties were obtained by the usual electrochemical techniques. The following behavior is predicted: when the particle comes into contact with the electrode by diffusion, the polyaniline layer takes the same potential as the electrode owing to the electric conduction; consequently, the whole polyaniline layer reacts at the electrode simultaneously as if the number of electrons transferred was very large. The anodic voltammetric peak, due to the oxidation of the radical cation to the dication, was controlled by diffusion of the particle. The diffusion coefficient obtained by the limiting current was half the value evaluated from the Stokes–Einstein relation. The steady-state voltammogram at a microelectrode and a rotating disk electrode showed a −0.2 V potential shift from the surface waves of the electrochemically synthesized polyaniline film, probably due to stabilization of the radical cation in the colloidal form. The number of the charge relevant to the electrode reaction was n=4.2×105, determined not only by the bulk electrolysis, but also by the analysis of chronoamperometric curves. The overall process is diffusion of the particle composed of n redox sites, followed by n parallel sluggish charge-transfer reactions.