Water–Polymer Interaction during Water Uptake

Abstract

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.

Predicting water transport in multilayer coatings

“…For a detailed description of the samples we refer to a previous paper [6]. Such systems are representative to multilayer coatings, which consist of a top layer that acts as a barrier and more hydrophilic layers under the top layer.…”

“…For more detailed description of NMR equipment and a discussion of NMR signal we refer to our previous works [5,6].…”

“…is an echo time [6]. The parameter a was estimated from the reference T 2 and self-diffusion constant and equals 5 [6].…”

“…Recently we have used high resolution NMR imaging to study water uptake in two-layer coatings [5,6]. The coatings consisted of a hydrophilic waterborne base coat and a hydrophobic solventborne top coat.…”

“…The ingress of water into a waterborne base coat through a protective top coat was visualized [5]. Identification of polymer phases and water in the base coat, plasticization of the polymer phases and evaluation of water mobility in the base coat were performed with relaxation analysis of NMR signal [6]. It was found that water in a saturated base coat is highly mobile and is more weakly bonded to the polymer matrix than in a partially saturated base coat.…”