NMR Imaging of Water Uptake in Multilayer Polymeric Films: Stressing the Role of Mechanical Stress

Abstract

The penetration of water into two-layer polymeric films of a hydrophilic base layer and hydrophobic top layer plays an important role in their performance. Little is known about the coupled effects of water uptake and stress in such films. To study such interactive phenomena, time-dependent distributions in the film are needed, which cannot be provided by traditional techniques. In this study, high-resolution NMR imaging was used to measure water profiles, showing that applied stress increased both the uptake rate and the amount of absorbed water. A model was formulated to describe the process, using the barrier properties of and the chemical potential differences over the top coat. On the basis of this, the diffusivity in the top layer and stress contribution were estimated. The results show that external stresses significantly influence water penetration into multilayer films.

Predicting water transport in multilayer coatings

“…The signal increase is proportional to the amount of water [5]. An important observation is that there is signal increase near the base coat/glass interface already in the first profiles, indicating that water quickly equilibrates in the base coat.…”

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

“…The permeability of the top coat in a two-layered system can be measured with a D 2 O/H 2 O exchange experiment [5]. The amount of water can be measured with NMR.…”

“…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 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].…”