Title: Effect of molecular shape on rotation under severe confinement

Abstract

Orientational structure and dynamics of molecules is known to be affected by confinement in space comparable in size to the molecule itself. ZSM-5 with porous channels of ≈0.55 nm is such a porous medium, which offers a strict spatial confinement on low molecular weight hydrocarbons. An important factor that determines these properties is the shape of the confined molecules. In this work, we employed molecular dynamics simulation to study the orientational structure and dynamics of four molecules that differ in shape but have similar kinetic diameters and moments of inertia, confined in ZSM-5. The effect of molecular shape on the orientational structure and dynamics of propane, acetonitrile, acetaldehyde and acetone in ZSM-5 is studied by means of probing the differences in the orientational distribution of molecules in the ZSM-5 channels, and extracting time scales of the decay of correlation functions related to rotational motion. Orientational correlation functions of all the four molecules exhibit two regimes of rotational motion. While the short time regime represents free rotation of the molecules before they collide with the pore walls, the long time orientational jumps driven by inter-channel migrations give rise to a very slow varying second regime. Of the molecules studied, orientational structuremore » and dynamics of propane is found to be least affected by confinement under ZSM-5, whereas charge and shape asymmetry of other molecules makes their interchannel migration-driven rotation slow. The time scales involved in the rotational motion for the molecules studied are compared with similar studies reported in literature. Lastly, this study reveals the important role that molecular shape plays in the behavior of confined molecules.« less

Authors:

Dhiman, Indu  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-6072-755X"
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Bhowmik, Debsindhu  ^[2];

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• Search DOE PAGES for ORCID "0000-0001-7770-9091"
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Shrestha, Utsab R.  ^[3];

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• Search DOE PAGES for ORCID "0000-0001-6985-6657"
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Cole, David R. ^[4]; Gautam, Siddharth ^[4]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Computational Science and Engineering Division
3. University of Tennessee/Oak Ridge National Laboratory, Oak Ridge, TN (United States). Center for Molecular Biophysics
4. The Ohio State University, Columbus, OH (United States). School of Earth Sciences

Publication Date:

2018-01-31

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division

OSTI Identifier:

1422992

Alternate Identifier(s):

OSTI ID: 1573263

Grant/Contract Number:  

AC05-00OR22725; SC0006878

Resource Type:

Accepted Manuscript

Journal Name:

Chemical Engineering Science

Additional Journal Information:

Journal Volume: 180; Journal Issue: C; Journal ID: ISSN 0009-2509

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 42 ENGINEERING; ZSM-5; Molecular rotation; Propane; Acetone; Acetaldehyde; Acetonitrile