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Propane-Water Mixtures Confined within Cylindrical Silica Nano-Pores: Structural and Dynamical Properties probed by Molecular Dynamics

Le, TTB; Striolo, A; Gautam, S; Cole, DR; (2017) Propane-Water Mixtures Confined within Cylindrical Silica Nano-Pores: Structural and Dynamical Properties probed by Molecular Dynamics. Langmuir , 33 (42) pp. 11310-11320. 10.1021/acs.langmuir.7b03093. Green open access

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Abstract

Despite the multiple length and time scales over which fluid-mineral interactions occur, interfacial phenomena control the exchange of matter and impact the nature of multiphase flow, as well as the reactivity of C-O-H fluids in geologic systems. In general, the properties of confined fluids, and their influence on porous geologic phenomena are much less well understood compared to those of bulk fluids. We used equilibrium molecular dynamics simulations to study fluid systems composed of propane and water, at different compositions, confined within cylindrical pores of diameter ~16 Å carved out of amorphous silica. The simulations are conduced within a single cylindrical pore. In the simulated system all the dangling silicon and oxygen atoms were saturated with hydroxyl groups and hydrogen atoms, respectively, yielding a total surface density of 3.8 -OH/nm2. Simulations were performed at 300 K, at different bulk propane pressures, and varying the composition of the system. The structure of the confined fluids was quantified in terms of the molecular distribution of the various molecules within the pore as well as their orientation. This allowed us to quantify the hydrogen bond network and to observe the segregation of propane near the pore center. Transport properties were quantified in terms of the mean square displacement in the direction parallel to the pore axis, which allows us to extract self-diffusion coefficients. The diffusivity of propane in the cylindrical pore was found to depend on pressure, as well as on the amount of water present. It was found that the propane self-diffusion coefficient decreases with increasing water loading because of the formation of water bridges across the silica pores, at sufficiently high water content, which hinder propane transport. The rotational diffusion, the lifespan of hydrogen bonds, and the residence time of water molecules at contact with the silica substrate were quantified from the simulated trajectories using the appropriate auto-correlation functions. The simulations contribute to a better understanding of the molecular phenomena relevant to the behavior of fluids in the sub-surface.

Type: Article
Title: Propane-Water Mixtures Confined within Cylindrical Silica Nano-Pores: Structural and Dynamical Properties probed by Molecular Dynamics
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acs.langmuir.7b03093
Publisher version: http://doi.org/10.1021/acs.langmuir.7b03093
Language: English
Additional information: Copyright © 2017 American Chemical Society. This is an open access article published under an ACS AuthorChoice License (http://pubs.acs.org/page/policy/authorchoice_termsofuse.html), which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
Keywords: Adsorption; Diffusion; Structure-Transport Relation
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/1575405
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