Redox reactions of polyaniline-coated latex suspensions

Electrically conducting redox-active particles were synthesized by coating near-monodisperse, micrometer-sized polystyrene latex particles (1.62 mum diameter) with polyaniline at 0 degreesC. This low-temperature synthesis route ensured that high-quality polyaniline was produced. The purified particles were dispersed in an aqueous acidic surfactant solution. According to bulk electrolysis measurements, the reduction of each latex particle leads to the transfer of n = 1.7 x 10(9) electrons. The acidic suspension showed a cathodic peak at 0.10 V and a very small anodic peak at 0.20 V. The former feature corresponds to the reduction wave, i.e., the conversion of polyaniline from its electrically conducting emeraldine form to its insulating leucoemeraldine state. The cathodic wave varied from a surface wave at lower latex concentration to a diffusion wave at higher latex concentration. The peak current varied linearly with the square root of the potential scan rate, giving a value of n similar to that obtained from bulk electrolysis. The irreversibility of the voltammogram, i.e., the disappearance of the anodic wave, was ascribed to such a short time of collision with the electrode that the conducting zone can propagate only to a small domain near the collision point.