Atomistic-level understanding of the interfacial behavior of ionic liquids (ILs) confined in slit-like nanopores is of both fundamental and practical interest. Molecular dynamics (MD) is an efficient and robust approach to characterize the properties of confined systems in contrast with some limitations in direct experimental measurements at low-dimensions. In this research, MD simulations are used to study the biocompatible IL cholinium glycinate, [Cho][Gly], confined between two parallel plates of rutile or graphite, with the separation distance of 24 Å along the z-direction. As expected, both the microscopic local structure and dynamical behavior of the confined IL are very heterogeneous and depend effectively on the position of the ions to the pore walls. The ion z-density profile is used for segmentation of the inter-wall space into a central region and two outer layers. The behavior of ions in the central region is very similar to the bulk IL, while the behavior of the arranged ionic layers adjacent to the pore walls shows the clear deviation from the bulk IL due to confinement. In general, the confined IL shows a “solid-like” dynamics at T = 353 K, especially in the outer layers near the walls as well as in the z-direction. The presence of the “IL-rutile wall” electrostatic interaction and hydrogen bonding (H-bonding) causes a significant difference in the local structure and very sluggish dynamics of the IL adjacent to the rutile walls vs the graphite walls. Simulation reveals a significant decrease in the average number of key cation–anion H-bonds at the outer layers relative to the central regions of both confined systems. The recognized [Cho]+⋯[Gly]−⋯[Cho]+ bridge structure at the central region is lost in the vicinity of the rutile walls due to inaccessibility of the hydroxyl hydrogen atom, which forms a stable H-bond with the rutile oxygen site. However, another unprecedented [Gly]− bridge is confirmed and preserved near the graphite walls, and [Cho]+ cations prefer to stay parallel to the wall surface to form the van der Waals dispersion interactions with the uncharged graphite walls.
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7 June 2022
Research Article|
June 01 2022
Tracing the origin of heterogeneities in the local structure and very sluggish dynamics of [Cho][Gly] ionic liquid confined between rutile and graphite slit nanopores: A MD study
Farzad Khorrami;
Farzad Khorrami
1
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS)
, Zanjan 45137-66731, Iran
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Mohammad H. Kowsari
Mohammad H. Kowsari
a)
1
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS)
, Zanjan 45137-66731, Iran
2
Center for Research in Climate Change and Global Warming (CRCC), Institute for Advanced Studies in Basic Sciences (IASBS)
, Zanjan 45137-66731, Iran
a)Author to whom correspondence should be addressed: mohammad.kowsari@gmail.com and mhkowsari@iasbs.ac.ir. Tel.: +98 24 3315 2258. Fax: +98 24 3315 3232
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a)Author to whom correspondence should be addressed: mohammad.kowsari@gmail.com and mhkowsari@iasbs.ac.ir. Tel.: +98 24 3315 2258. Fax: +98 24 3315 3232
J. Chem. Phys. 156, 214701 (2022)
Article history
Received:
March 22 2022
Accepted:
May 11 2022
Citation
Farzad Khorrami, Mohammad H. Kowsari; Tracing the origin of heterogeneities in the local structure and very sluggish dynamics of [Cho][Gly] ionic liquid confined between rutile and graphite slit nanopores: A MD study. J. Chem. Phys. 7 June 2022; 156 (21): 214701. https://doi.org/10.1063/5.0092381
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