DYNAMICS OF WATER IN THE POLY(ETHYLENE OXIDE) HYDRATION SHELL - A QUASI-ELASTIC NEUTRON-SCATTERING STUDY

A quasi elastic neutron-scattering (QENS) experiment has been carried out to elucidate the nature of the dynamic hydration of perdeuterated poly(ethylene oxide) (PEO) in aqueous solution. A line-shape analysis of the QENS spectra clearly shows evidence for a hydration zone around the polymer, the dynamic properties of which are significantly different from those of the bulk. The data were analyzed in terms of a two-phase model assuming Fick diffusion for both phases and allowing for exchange between the populations. The mobility of the hydration water is on the order of 10(-11) m(2) s(-1). This value corresponds to the rate of diffusion of the polymer as determined by pulsed-field gradient NMR (PFG-NMR). The average residence time of water in the polymer's hydration shell is approximately 10(-11) s. Assuming the hydration water mimics the motion of the chain, a Zimm-type scattering law was fitted to the data. Although line shapes are well described, the mobility of bulk water is inconsistent with the literature value.