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Title: Density of hydrophobically confined deeply cooled water investigated by small angle X-ray scattering

Water’s behavior near hydrophobic surfaces has attracted great attention due to chemical and geological applications. Here, we report small angle X-ray scattering (SAXS) studies of water confined in the hydrophobic nanoporous carbon material, CMK-1-14, from ambient to deeply cooled temperatures. By monitoring the scattering intensity of the first Bragg peak, which is directly related to the scattering length density contrast between the carbon matrix and the confined water, the average density of the hydrophobically confined water was determined from 300 K to 150 K at ambient pressure. Furthermore, differential scanning calorimetry and X-ray diffraction measurements showed that the majority of such hydrophobically confined water did not crystallize in the investigated temperature range. By exploiting the fast speed of SAXS measurements and the continuous temperature ramping, the average density profile and the deduced thermal expansion coefficient (α{sub p}) were obtained. We found that the well-known density maximum of water at 277 K downshifted to 260 K, and the density minimum which has been observed in hydrophilic confinement disappeared. In addition, the previously measured large density decreasing of 18% at low temperature was recalibrated to a more reasonable 10% instead. Consequently, the recalculated α{sub p} peak was found to be quite similarmore » to that of the water confined in hydrophilic MCM-41-S-15 suggesting an intrinsic property of water, which does not sensitively depend on the confinement surface.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [1]
  1. Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan (China)
  2. (United States)
  3. Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
  4. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China)
Publication Date:
OSTI Identifier:
22493606
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BRAGG CURVE; CALORIMETRY; CARBON; DENSITY; NANOMATERIALS; POROUS MATERIALS; SCATTERING LENGTHS; SMALL ANGLE SCATTERING; SURFACES; TEMPERATURE DEPENDENCE; THERMAL EXPANSION; VELOCITY; WATER; X-RAY DIFFRACTION