Multilayer assemblies of redox polyelectrolytes

Polyelectrolyte multilayers containing electrochemically active viologen units have been constructed using the layer-by-layer deposition technique with poly(styrenesulfonate) and poly(butanylviologen) as polyanion and polycation, respectively. All redox active material is electrochemically addressable in multilayers made from these polymers. Cyclic voltammetry, ellipsometry, and W-vis spectroscopy indicate a systematic dependence of the amount of material contained in these ultrathin films on the number of deposition cycles, although initial layers are significantly thinner. When the distance between a redox active layer and the electrode was varied by interposing non-electrochemically active layer pairs, it was determined that the material within the redox active layer was distributed over a distance of at least 2.5 layer pairs away from the nominal location of the redox active layer. This evidence for extensive interpenetration between layers was confirmed using variable-angle XPS, which revealed a 1:1 stoichiometry between charges on positive and negative polyelectrolytes in multilayers. No salt ions were detected in multilayers.