8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Thu 811:10-14:00P7.127Structure and dynamics of low-temperature waterconfined in porous silicaKoji Yoshida, 1 Toshio Yamaguchi, 2 Shigeharu Kittaka, 3 Marie-Claire Bellissent-Funel, 4 Peter Fouquet, 5 and Daniel Bowron 61 Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, 814-0180, Fukuoka, Japan2 Fukuoka University, Fukuoka, Japan3 Okayama University of Science, Okayama, Japan4 Laboratoire Léon Brillouin CEA-CNRS, Gif-sur-Yvette Cedex, France5 Institut Laue-Langevin, Grenoble Cedex 9, France6 Rutherford Appleton Laboratory, Oxon, United KingdomWater confined in nano-scale pore occurs under various conditions, such as water in rocks, proteinsand membranes. MCM-41 is a micelle-templated mesoporous silica that consists of a hexagonallypacked array of cylindrical pores that have a uniform size distribution. In order to understand thelow temperature behavior of confined water, we have performed neutron diffraction with isotopicsubstitution (NDIS) at 298 and 173 K and neutron spin echo (NSE) measurements of both monolayerand capillary condensed water confined in MCM-41 C 10 (pore diameter 2. 10 nm) in the temperaturerange between 298 - 180 K. Radial distribution functions from the NDIS data revealed thatthe confined water in the central region of the pore space develops tetrahedral-like water structureat 173 K, compared with that at 298 K, although the homogeneous nucleation of ice does not takeplace in the temperature range measured. Additionally it appears that the structure of surface waterhardly changes because of the strong interaction with the pore wall. The intermediate scatteringfunctions from the NSE data showed that monolayer and capillary condensed D 2 O has a wide distributionof relaxation time. For the capillary condensed water, the relaxation times of D 2 O followthe Vogel-Tamman-Fulcher equation remarkably well between 298 and 220 K, whereas below 220K the system shows an Arrhenius type behavior, i. e. , a strong-fragile dynamic crossover occurs.In contrast, for the monolayer sample, the strong-fragile dynamic crossover was not found in thetemperate range measured; the temperature dependence of the relaxation time simply displayedArrhenius type behavior. We conclude that the capillary condensed water is heterogeneous on itssurface and in the central part of the pores, and that the fragile-strong dynamic crossover wouldmost likely only occur in water found in the central part of the pore.127