Anomalous behavior of confined-supercooled water near the bulk water hypothetical 2 nd Critical Temperature
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P5.5.1
Anomalous behavior of confined-supercooled water near the bulk water hypothetical 2nd Critical Temperature F. Mansour*, R. M. Dimeo**, and H. Peemoeller†* *Department of Physics, University of Waterloo, Waterloo ON, N2L 3G1 **NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive - Stop 8562 Gaithersburg, MD 20899-8562 . † Author to whom correspondence should be addressed. ABSTRACT High resolution inelastic neutron scattering measurements of the molecular dynamics of deeply supercooled water confined to a porous host, MCM-41 are reported. Results obtained near the critical temperature of water are discussed. Anomalous behavior near and below the glass transition temperature is also presented and discussed. Results are compared to those from earlier studies on supercooled water. INTRODUCTION When water is confined to small spaces it exhibits significant resemblance to supercooled water. Deep supercooling can be obtained by further cooling confined water. Appropriate confinement conditions can possibly render the critical temperature of water accessible. The effects of confinement on the molecular properties of water have attracted a lot of interest in the past few decades [1-12, 14, 15, 26]. Understanding the behavior of this fascinating hydrogen bonded fluid upon confinement is of value to a vast array of problems ranging from oil recovery and geo-chemical applications to biophysical interactions, medical imaging, colloid and interface chemistry, and food product quality. In this paper we present results of a series of inelastic incoherent neutron scattering measurements of water in MCM-41. Previous measurements on water in MCM-41 suggested dynamics on time scales of picoseconds. Here we extend these measurements using very high resolution neutron spectroscopy and find that the confined water exhibits dynamics three orders of magnitude slower than the previous measurements. Experimental detail, full instrument description and data analysis, presented briefly here are available in full detail elsewhere [24]. In this summary we focus on the interconnection between freezing point depression, glass transition temperature shift, confinement, supercooling and relaxation time distributions in water. In this experiment we have used MCM-41 samples synthesized at the University of Waterloo using a liquid crystal template. The final molar composition of the material forming the liquid crystal was: 1.0 SiO2, 0.19 TMAOH (tetramethyl-ammonium hydroxide pentahydrate, 97%, Sigma) 0.27 CTABR (Cetyltrimethyl ammonium bromide, 99%, Aldrich), 40 H2O. The final product was filtered, calcined and the pores saturated with H2O. The MCM-41 pore size distribution showed a very narrow range of pores centered around 27.5 Å for an average pore diameter. The X-ray diffraction pattern from the material confirmed a hexagonal distribution of the MCM-41 channels[24].
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NEUTRON SCATTERING MEASUREMENT DETAILS Neutron scattering measurements were carried out at the NIST Center for Neutron Rese
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