Dynamic Properties of Water Confined in Sephadex G15 Gel by Quasi-Elastic Neutron Scattering and Neutron Spin Echo Measurements

The dynamic properties of water confined in Sephadex G15 gel were investigated over the temperature range of 275-320K at a hydration level h (= mass of water/mass of dry G15 gel) of 0.38, where both bound water melting at 258-268K and unfrozen water are present, by using quasi-elastic neutron scattering (QENS) and neutron spin echo (NSE) techniques. The QENS data showed that, at 290K, the water molecules perform local motions characterized by a diffusion coefficient D-local of (0.65 +/- 0.05) x 10(-5) cm(2)s(-1) and that the diffusion is limited to some volume estimated as a sphere with a radius of 4.4 angstrom. The Arrhenius plots of the relaxation time of water gave the activation energy of 44.2 +/- 1.5 kJ mol(-1), which is somewhat larger than the value (15-36 kJ mol(-1)) of water confined in MCM-41 C10 (pore diameter 21 angstrom). This finding suggests that water molecules in G15 gel are strongly bound to the hydroxy groups of the crosslinked substrates.