Different States of Water in Hydrogels?

Atomistically detailed molecular dynamics simulations of a hydrogel of poly(vinyl alcohol) have been performed. These have been analysed for the water mobility at 250, 300 and 375 K. Only the re-orientation at 250 K but not the translation of the water molecules shows a bimodal distribution of correlation times which may be interpreted by the existence of two different dynamical states of water. At higher temperatures, however, there is no evidence for different states of water. Moreover, water molecules in contact with the polymer relax more slowly than others, also at low temperatures. Therefore, the concept that "free" water can freeze upon cooling of a hydrogel whereas "bound" water cannot, needs to be revised. 2 Polymers swollen to a high degree by water play a central role in many areas of science and technology, from cell biology over food components to technical separation membranes and personal hygiene products. The role of the water in these systems has been under investig...