Dielectric properties of polyelectrolyte multilayers

A relatively new technique based on the sequential adsorption of oppositely charged polymers affords the fabrication of multilayer thin films with controlled molecular architectures. In this work, we report the first study on the impedance and dielectric characteristics of multilayer films created by the sequential adsorption of layers of poly(allylamine hydrochloride) (PAH) with poly(acrylic acid) (PAA) and sulfonated polystyrene (SPS). We show large changes in the dielectric characteristics of these films with changes in temperature, moisture content, and deposition conditions. In particular, large increases in the conductivity and dielectric constant as the temperature and moisture content are increased were interpreted in terms of a change in the mobility and effective concentration of small ions in the film. A small but nonnegligible concentration of such ions was found to be incorporated into these films at a level that depends on the solution processing parameters such as the pH and salt content.