Thermal Behavior, Structure, and Dynamic Properties of Water Confined in Polymer Gel Sephadex G15

Presenter: 

Kanae Ito

Authors: 

K. Ito, K. Yoshida, K. Ujimoto, M.-C. Bellissent-Funel, T. Yamaguchi

Author Affiliation: 

Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan, Fukuoka 814-0180, Japan Laboratoire Leon Brillouin (CEA-CNRS), CEA Saclay, 91191 Gif-sur-Yvette Cedex, France Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA

Abstract: 

The thermal behavior, structure, and dynamic properties of water confined in polymer gel Sephadex G15 were investigated over a temperature range of 298-173K as a function of hydration level (g H2O/g dry gel) by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and quasi-elastic neutron scattering (QENS) and neutron spin echo (NSE) measurements. The DSC data showed that there are three states of water in G15 gel: free water, freezable bound water, and unfrozen water. The X-ray radial distribution functions revealed that the tetrahedral-like hydrogen bonded network of confined water is largely distorted, compared with the bulk water. The QENS data showed that the water molecules perform local motions characterized by a diffusion coefficient of (0.65 +/- 0.05) x 10-5cm2s-1 within a sphere with a radius of 4.4 Angstrom. The Arrhenius plots of the relaxation time of water gave an activation energy of 44.2 +/- 1.5 kJmol-1, which is somewhat larger than the value of 15-36kJmol-1 of capillary condensed water confined in mesoporous silica MCM-41 C10 (pore diameter 21 Angstrom). The present findings suggest that water molecules in G15 gels are strongly bound to the hydroxyl groups of the gel matrix.