title: Temperature dependence of structure and density for D₂O confined in MCM-41-S.
abstract: Using neutron diffraction, we have tracked the temperature dependence of structural properties for heavy water confined in the nanoporous silica matrix MCM-41-S. By observing the correlation peak corresponding to the pore-pore distance, which is determined by the scattering contrast between the silica and the water, we monitored the density of the confined water. Concurrently, we studied the prominent first diffraction peak of D(2)O at ≈ 1.8 Å(-1), which furnishes information on the microscopic arrangement of the water molecules. The data show the presence of a density maximum at ≈ 275 K (± 10 K), a property similar to bulk water, and the occurrence of a density minimum at ≈ 180 K (± 10 K). The prominent diffraction peak of D(2)O is found to shift and sharpen over a wide T range from 200 to 270 K, reflecting structural changes that are strongly correlated with the changes in density. We also observe the continuous formation of external ice, arising from water expelled from the pores while expansion takes place within the pores. An efficient method for monitoring the density of the confined D(2)O using a triple-axis spectrometer is demonstrated.
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Kamitakahara
authors.forename: Antonio
authors.initials: A
authors.lastname: Faraone
authors.forename: Kao-Hsiang
authors.initials: KH
authors.lastname: Liu
authors.forename: Chung-Yuan
authors.initials: CY
authors.lastname: Mou
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry*; D006860:Hydrogen Bonding; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: C509968:MCM-41; D012822:Silicon Dioxide; D017666:Deuterium Oxide