Vibrational spectroscopic studies of the dynamics and perturbation of water in polymeric films

This paper reviews the current state of knowledge of how the dynamics and interactions of water are altered on sorption into a polymer. In particular, the role of infrared and Raman spectroscopies is examined, based on work in our group (and in other laboratories). Key questions as to the relevance of water-water and water-polymer interactions for the determination of the dynamic properties of 'bound' water are defined and addressed. It is concluded that water 'confined' to polymeric voids (or defects) is motionally hindered by strong water-polymer intermolecular forces. However, water-water interactions are loosened, the water network is 'broken' (to a degree which depends on the hydration level) and several water 'types' may be distinguished, depending on the time scale of the particular experiment. A non-uniform distribution of motional correlations in space and time is inferred, as maybe expected for such a heterogeneous material. (C) 2002 Elsevier Science B V. All rights reserved.