Incoherent quasi-elastic neutron scattering in water-PEG solutions

We report high-resolution (7 mu eV, half-width at half-maximum HWHM) incoherent quasi-elastic neutron scattering data performed on mixtures of Poly(Ethylene Glycol), molecular weight (M.W.) 600 Da, with water. Both samples were prepared using H2O and D2O in order to be able to separate the polymer dynamics and the hydration water dynamics. Data analysis gives a diffusion coefficient for the polymer which is found to depend on concentration, and suggests that the dynamics of hydration water are much slower than that of bulk water. Moreover, the hydration water exhibits dynamical behaviour typical of confined liquids, and the size of the confinement region increases with water content. Additional properties are explained on the basis of previous results so furnishing a complete characterization of the hydration and of the diffusive properties of these H-bonded systems. These results give a reference picture for the comprehension of the water interaction with natural polymers. (C) 1998 Elsevier Science B.V. All rights reserved.