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Title: Translational diffusion of water inside hydrophobic carbon micropores studied by neutron spectroscopy and molecular dynamics simulation

Journal Article · · Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
 [1];  [2];  [3];  [4];  [5];  [6];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Science Division
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Instrument and Source Division
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS)
  6. American Technical Trading, Inc., Pleasantville, NY (United States)
+ Show Author Affiliations

When water molecules are confined to nanoscale spacings, such as in the nanometer-size pores of activated carbon fiber (ACF), their freezing point gets suppressed down to very low temperatures (~150K), leading to a metastable liquid state with remarkable physical properties. In this study, we have investigated the ambient pressure diffusive dynamics of water in microporous Kynol ACF-10 (average pore size ~11.6Å, with primarily slit-like pores) from temperature T=280 K in its stable liquid state down to T=230 K into the metastable supercooled phase. The observed characteristic relaxation times and diffusion coefficients are found to be, respectively, higher and lower than those in bulk water, indicating a slowing down of the water mobility with decreasing temperature. The observed temperature-dependent average relaxation time <τ> when compared to previous findings indicate that it is the width of the slit pores—not their curvature—that primarily affects the dynamics of water for pore sizes larger than 10 Å. The experimental observations are compared to complementary molecular dynamics simulations of a model system, in which we studied the diffusion of water within the 11.6 Å gap of two parallel graphene sheets. Also, we find generally a reasonable agreement between the observed and calculated relaxation times at the low momentum transfer Q(Q ≤ 0.9Å-1). At high Q, however, where localized dynamics becomes relevant, this ideal system does not satisfactorily reproduce the measurements. Consequently, the simulations are compared to the experiments at low Q, where the two can be best reconciled. Lastly, the best agreement is obtained for the diffusion parameter D associated with the hydrogen-site when a representative stretched exponential function, rather than the standard bimodal exponential model, is used to parametrize the self-correlation function I(Q,t).

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1261423
Alternate ID(s):
OSTI ID: 1181535; OSTI ID: 1265416
Journal Information:
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, Vol. 91, Issue 2; ISSN 1539-3755
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 15 works
Citation information provided by
Web of Science

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Cited By (3)

Effect of pore geometry on nanoconfined water transport behavior journal May 2019
Self-diffusion coefficient of bulk and confined water: a critical review of classical molecular simulation studies journal August 2018
Self-diffusion coefficient of bulk and confined water: a critical review of classical molecular simulation studies text January 2018

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Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Water Diffusion
Confined Fluids
Supercooled Water
Molecular Dynamics
Quasi-Elastic Neutron Scattering