Hydration cycling in redox active LBL self-assembled polyelectrolyte multilayers

Direct evidence of a net gain or loss of water by redox switching self-assembled redox active polyelectrolyte multilayers from/to the liquid electrolyte has been obtained by “in situ” infrared spectroscopy. This is in agreement with EQCM microgravimetry and ellipsometry thickness change upon oxidation–reduction cycles due to the exchange of ions and solvent, which results in film swelling. Infrared evidence of a change in the environment of functional groups, i.e., SO3-, NH3+ and bipyridines in the films formed by poly(allylamine) modified covalently by an osmium bipyridine–pyridine complex (PAH-Os) and polystyrene sulfonate (PSS) has also been obtained by SNIFTIRS. This has been interpreted as break of the polycation–polyanion chain electrostatic interaction by mobile cations and anions from the solution forming ion pairs with the polyelectrolyte chains in the film during “break in”.