Water-Polymer Interaction during Water Uptake

Water uptake by multilayer films plays an important role in their performance. Individual layers may consist of different polymeric phases. Understanding the water uptake in such systems requires knowledge of the water distribution, its state in the polymer, and influence on the polymeric phases. This study illustrates the application of high-resolution NMR and relaxometry for measuring water distributions and evaluating water–polymer interactions. We studied water uptake in a two-layered base coat/top coat system, where the base coat consisted of acrylic, polyurethane, pigment particles, and a polymeric dispersant. Water and the polymer phases in the base coat were identified with NMR relaxometry. The water diffusivity in the base coat was determined. At high water contents water is highly mobile and is loosely bonded to the polymer. Reversible plasticization of the dispersant was observed. The polymeric dispersant seems to play a key role in the sorption of water by the coating.