Formation, chemical composition, and structure of polyelectrolyte-nanoparticle multilayer films

The buildup and structure of multilayer films containing cationic polyelectrolyte and silica nanoparticles have been studied by means of ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. Emphasis was placed on the effect of ionic strength on the adsorption behavior and structure formation. Consecutive exposure of a silica substrate to low ionic strength solutions containing polyelectrolyte and nanoparticles resulted in the formation of stable adsorbed films with a reproducible stratified multilayer structure. The films formed in high ionic strength solutions were initially much thicker but also clearly less stable. A significant desorption was observed to take place in conjunction with the second exposure to silica nanoparticles. The effect of electrolyte concentration is discussed in terms of a salt-induced glass-liquid transition, above which the relaxation rate in the adsorbed composite film increases and thereby hinders the formation of multilayer structures.