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Title: Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane

Fluids confined in nanopores exhibit significant deviations in their structure and dynamics from the bulk behavior. Although phase, structural and diffusive behaviors of confined fluids have been investigated and reported extensively, confinement effects on the vibrational properties are less understood. Here, we study the vibrational behavior of propane confined in 1.5 nm nanopores of MCM-41-S using inelastic neutron scattering (INS) and molecular dynamics (MD) simulations. Vibrational spectra have been obtained from INS data as functions of temperature and pressure. At ambient pressure, a strong quasielastic signal observed in the INS spectrum at 80 K suggests that confined propane remains liquid below the bulk phase melting point of 85 K. The quasielastic signal is heavily suppressed when either the pressure is increased to 1 kbar, or the temperature is lowered to 30 K, indicating solidification of pore-confined propane. Confinement in MCM-41-S pores results in a glass-like state of propane that exhibits a relatively featureless low-energy vibrational spectrum compared to the bulk crystalline propane. Increasing the pressure to 3 kbar results in hardening of the intermolecular and methyl torsional modes. The INS data are used for estimating the isochoric specific heat of confined propane, which is compared with the specific heat ofmore » bulk propane reported in literature. Data from MD simulations is used to calculate the vibrational power spectra that agree qualitatively with the experimental data. Simulation data also suggests a reduction in the structural ordering (positional, orientational and intramolecular) of propane under confinement.« less
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [3] ;  [4] ;  [1]
  1. The Ohio State Univ., Columbus, OH (United States). School of Earth Sciences
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Jilin Univ., Changchun (China). State Key Lab. of Inorganic Synthesis and Preparative Chemistry and College of Chemistry
Publication Date:
Grant/Contract Number:
AC05-00OR22725; SC0006878
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: TBD; Journal Issue: TBD; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Contributing Orgs:
Science and Technology Facilities Council (STFC), Daresbury (United Kingdom). Daresbury Lab.; Rensselaer Polytechnic Inst., Troy, NY (United States)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1462830

Gautam, Siddharth, Kolesnikov, Alexander I., Rother, Gernot, Dai, Sheng, Qiao, Zhen-An, and Cole, David R.. Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane. United States: N. p., Web. doi:10.1021/acs.jpca.8b05028.
Gautam, Siddharth, Kolesnikov, Alexander I., Rother, Gernot, Dai, Sheng, Qiao, Zhen-An, & Cole, David R.. Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane. United States. doi:10.1021/acs.jpca.8b05028.
Gautam, Siddharth, Kolesnikov, Alexander I., Rother, Gernot, Dai, Sheng, Qiao, Zhen-An, and Cole, David R.. 2018. "Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane". United States. doi:10.1021/acs.jpca.8b05028.
@article{osti_1462830,
title = {Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane},
author = {Gautam, Siddharth and Kolesnikov, Alexander I. and Rother, Gernot and Dai, Sheng and Qiao, Zhen-An and Cole, David R.},
abstractNote = {Fluids confined in nanopores exhibit significant deviations in their structure and dynamics from the bulk behavior. Although phase, structural and diffusive behaviors of confined fluids have been investigated and reported extensively, confinement effects on the vibrational properties are less understood. Here, we study the vibrational behavior of propane confined in 1.5 nm nanopores of MCM-41-S using inelastic neutron scattering (INS) and molecular dynamics (MD) simulations. Vibrational spectra have been obtained from INS data as functions of temperature and pressure. At ambient pressure, a strong quasielastic signal observed in the INS spectrum at 80 K suggests that confined propane remains liquid below the bulk phase melting point of 85 K. The quasielastic signal is heavily suppressed when either the pressure is increased to 1 kbar, or the temperature is lowered to 30 K, indicating solidification of pore-confined propane. Confinement in MCM-41-S pores results in a glass-like state of propane that exhibits a relatively featureless low-energy vibrational spectrum compared to the bulk crystalline propane. Increasing the pressure to 3 kbar results in hardening of the intermolecular and methyl torsional modes. The INS data are used for estimating the isochoric specific heat of confined propane, which is compared with the specific heat of bulk propane reported in literature. Data from MD simulations is used to calculate the vibrational power spectra that agree qualitatively with the experimental data. Simulation data also suggests a reduction in the structural ordering (positional, orientational and intramolecular) of propane under confinement.},
doi = {10.1021/acs.jpca.8b05028},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = TBD,
volume = TBD,
place = {United States},
year = {2018},
month = {7}
}