A quartz crystal microbalance method of quantifying water-ion pair interactions in polyelectrolyte multilayers

The alternate adsorption of polycations and polyanions on a substrate yields multilayer structures that have highly adaptable properties. These polyelectrolyte multilayers (PEMs) have promising applications in batteries, drug-delivery and protective coating systems. The three major components of PEMs are polymer, water and salt ions, all of which largely influence the PEM properties. In this talk, we discuss the influence of salt and polyelectrolyte on the water content of the PEM- specifically, the water associated with the polycation-polyanion (intrinsic) ion pairs, “i”. Attempts to quantify i for polyelectrolyte systems are few and complex. Here, using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry, we determine values of i for poly(diallyldimethylammonium)/polystyrene sulfonate PEMs. These results provide an understanding of water and ion-pair relationships and aim to provide a universal technique for all PEM systems.