NMR studies of the effect of adsorbed water on polyelectrolyte multilayer films in the solid state

Fast-MAS H-1 NMR is used to probe the structure and dynamics of the adsorbed water and polymer components in polyelectrolyte multilayer (PEM) films and the bulk polyelectrolyte complex (PEC). The films, ranging in size from a single layer to 5 bilayers, consist of poly(diallyl dimethylammonium chloride), PDADMAC, and poly(sodium-4-styrenesulfonate), PSS, adsorbed onto colloidal silica. Relaxation and line width measurements show that the adsorbed water is less mobile in the films than in the analogous PEC. The environment of the water throughout the film is found to be affected by the nature of the outer layer with the water displaying a higher mobility and chemical shift when PDADMAC forms the outer layer. Relaxation measurements, together with H-1 double-quantum (DQ) NMR experiments, reveal that polymer dynamics in the PEMs are strongly influenced by the layer number and water content. 2D spin diffusion and DQ NMR are used to detect polymer-polymer and water-polymer association. The results support the diffuse interpenetrating model of the different layers and a partitioning of the water to the PSS component and to the surface layer.