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The new backscattering spectrometer (BASIS) of the
Spallation Neutron Source at ORNL provides an
important advance in studying water dynamics on
mineral and other oxide surfaces. This instrument
provides a significant increase in energy resolution
together with a broad dynamic range for quasielastic
neutron scattering measurements of the dynamic
transition of hydration layers on the surface of
nano-powder rutile (TiO2).
Experimentation linked with supporting molecular
dynamics simulations by Mamontov et al. (2007)
indicate the presence of two distinct aspects of the
diffusional dynamics of water within the outermost
hydration layer on rutile: a faster localized
motion component and a slower translational motion
component. Measurements of this L3 hydration layer
indicate that both components obey Arrhenius laws,
with no evidence of a dynamic crossover from
non-Arrhenius to Arrhenius temperature dependence, a
feature observed on inner hydration layers. The
lack of a dynamic crossover is attributed to the
presence of fewer hydrogen bonds between water
molecules in the outermost hydration layer,
suggesting that this transition will not occur at
low hydration levels.
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MD snapshot
of rutile hydrated surface. Titanium atoms: yellow.
Oxygen atoms in rutile: cyan. Oxygen atoms in the L1
layer: green. Oxygen atoms in the L2
layer: blue. Oxygen atoms in the L3
layer: red. Hydrogen: white.
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For additional details, see:
Mamontov, E., Wesolowski, D. J.,
Vlcek, L., Cummings, P. T., Rosenqvist, J.,
Wang, W., and Cole, D. R., 2008, Dynamics of
Hydration Water on Rutile Studied by
Backscattering Neutron Spectroscopy and
Molecular Dynamics Simulation.
Journal of Physical Chemistry
C, ASAP Article; DOI: 10.1021/jp711965x
Mamontov, E., Vlcek, L.,
Wesolowski, D.J., Cummings, P.T., Wang, W.,
Anovitz, L.M.,
Rosenqvist, J., Brown,
C.M., and Garcia Sakai, V.,
2007, Dynamics and structure of hydration water
on rutile and cassiterite nanopowders studied by
quasielastic neutron scattering and molecular
dynamics simulations.
Journal of Physical Chemistry
C, 111, 4328-4341.
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