Swelling Degree of Polyelectrolyte Layers Determined by an Electrochemical Quartz Crystal Microbalance

Various polycations and polyanions were sequentially adsorbed onto the gold electrode of a quartz crystal microbalance with dissipation monitoring. The study focused on determining the adsorption kinetics, viscoelastic properties, and electroresponsivity of polyelectrolyte layers. For the first time, it was demonstrated that the structure (compact or expanded) of the layers can be determined by electroresponsivity. Viscoelastic modeling alone did not provide a conclusive answer as to whether the layers were compact or expanded. The study was further enriched by streaming potential and contact angle measurements, where polyelectrolyte multilayers were formed on mica. It was found that successive adsorption of layers led to periodic inversion of the zeta potential. Systematic differences were observed between the different top layers, which were explained by intermixing between layers. The presence or absence of interpenetration, as determined by the measurements of streaming potential and contact angles, correlated well with electroresponsivity.