Bound water governs the single-chain property of Poly(vinyl alcohol) in aqueous environments

The impact of water on the property of poly(vinyl alcohol) (PVA) has received much attention in recent decades. However, the underlying molecular mechanism is not well understood yet. Herein, by investigating the different stretching behaviors of PVA in aqueous and non-aqueous environments, the mechanism of how water affects the property of PVA is proposed. One water molecule interacts with two adjacent hydroxyl groups to form a water bridge on PVA. These water bridges are stable even upon highly stretching, which will act like staples on the PVA backbone. Accordingly, the single-chain property of PVA will be affected significantly. Moreover, on the basis of this work and previous studies, it can be concluded that PVA-water hydrogen bond (H-bond) is preferred over the intrachain and interchain H-bonds of PVA. The high priority of PVA-water H-bond and the stable water bridge may be the origin of the high moisture sensitivity of PVA materials.