Effects of Confinement and Pressure on Vibrational Behavior of Nano-confined Propane
- The Ohio State Univ., Columbus, OH (United States). School of Earth Sciences
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
- 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
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.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
- Contributing Organization:
- Science and Technology Facilities Council (STFC), Daresbury (United Kingdom). Daresbury Lab.; Rensselaer Polytechnic Inst., Troy, NY (United States)
- Grant/Contract Number:
- AC05-00OR22725; SC0006878
- OSTI ID:
- 1462830
- Journal Information:
- Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. TBD, Issue TBD; ISSN 1089-5639
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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