In situ determination of thickness and electrical properties of multilayers from weak polyelectrolytes

An electro-optical study of the role that the outermost layer plays in the behavior of a multilayer film of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) was carried out. The film surface was enriched with the chains of the last adsorbed polyelectrolyte when a fully ionized polymer was combined with nearly fully charged chains of the other polyelectrolyte. A distinct influence of the chain length on the critical frequency of relaxation of the electro-optical effect was demonstrated, indicating that polarization of condensed counterions of the last adsorbed polymer governs the behavior of the whole film. The multilayer growth, which was found to proceed via a series of adsorption-desorption steps, correlated well with the changes in the electro-optical effect. No indication was found, however, for participation of small ions from the film bulk in creation of the electro-optical effect.