Surface attached polyelectrolyte networks and their interaction with charged molecules in aqueous solutions

Surface attached polyelectrolyte networks (SAPNs) are one representative of a group of coatings that can be tailored to possess certain functional properties and adjust their properties according to a change in external parameters. Specifically, weak polyelectrolytes whose linear charge density is a function of the external pH-value of the solution were investigated in this work as a base material for the creation of ultra-thin, covalently attached networks with permantent cross-links.
It was found that swelling and charging processes of such SAPNs can be characterized an apparent diffusion coefficient with a magnitude of the order of 10-14 m²/s. The adsorption of oppositely charged polyions is a strong function of the pH-value of the polycation solutions. Specifically, at high pH-values and weakly charged polycations as adsorbing species, a high over-stoichometric adsorption was observed. The kinetics of the adsorption processes can be characeterized by an apparent diffusion coefficient with a magnitude of the order of 10-18 m²/s. The adsorption reaches thermodynamic equilibrium after sufficient long adsorption times. The SAPNs are suitable as substrates for Layer-by-Layer processing and provide the possibility of a very quick increase of the layer thickness with each adsorption step.