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Influence of ionic liquid film thickness on ion pair distributionsand orientations at graphene and vacuum interfaces
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Jilin University.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 32, 13559-13569 p.Article in journal (Refereed) Published
Abstract [en]

Microscopic structures, orientational preferences together with mass, number and electron density distributions of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) have been studied on a neutral hydrophobic graphene surface, and at the IL–vacuum interface using atomistic Molecular Dynamics simulations. At the IL–graphene interface, distinct mass, number and electron density distributions are observed oscillating into the bulk region with several compact structural layers. The imidazolium ring of [BMIM] cations lies preferentially flat on the graphene surface, with its methyl and butyl side chains elongated along the graphene surface. At the IL–vacuum interface, however, the distributions of [BMIM][PF6] ion pairs are strongly influenced by the thickness of IL film. With the increase of IL film thickness, the orientations of [BMIM] cations at the IL–vacuum interface change gradually from dominant flat distributions along the graphene surface to orientations where the imidazolium rings are either parallel or perpendicular to the IL–vacuum interface with tilted angles. The outmost layers are populated with alkyl groups and imparted with distinct hydrophobic character. The calculated radial distribution functions suggest that ionic structures of [BMIM][PF6] ion pairs in IL–graphene and IL–vacuum interfacial regions are significantly different from each other and also from that in bulk regions.

Place, publisher, year, edition, pages
2013. Vol. 15, no 32, 13559-13569 p.
Keyword [en]
graphene, ionic liquid
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-92706DOI: 10.1039/C3CP51226FISI: 000322401600033OAI: oai:DiVA.org:su-92706DiVA: diva2:641052
Available from: 2013-08-15 Created: 2013-08-15 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Electrostatic Interactions in Coarse-Grained Simulations: Implementations and Applications
Open this publication in new window or tab >>Electrostatic Interactions in Coarse-Grained Simulations: Implementations and Applications
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrostatic interactions between charged species play a prominent role in determining structures and states of physical system, leading to important technological and biological applications. In coarse-grained simulations, accurate description of electrostatic interactions is crucial in addressing physical phenomena at larger spatial and longer temporal scales.

In this thesis, we implement ENUF method, an abbreviation for Ewald summation based on non-uniform fast Fourier transform technique, into dissipative particle dynamics (DPD) scheme. With determined suitable parameters, the computational complexity of ENUF-DPD method is approximately described as O(N logN). The ENUF-DPD method is further validated by investigating dependence of polyelectrolyte conformations on charge fraction of polyelectrolyte and counterion valency of added salts, and studying of specific binding structures of dendrimers on amphiphilic membranes.

In coarse-grained simulations, electrostatic interactions are either explicitly calculated with suitable methods, or implicitly included in effective potentials. The effect of treatment fashion of electrostatic interactions on phase behavior of [BMIM][PF6] ionic liquid (IL) is systematically investigated. Our systematic analyses show that electrostatic interactions should be incorporated explicitly in development of effective potentials, as well as in coarse-grained simulations to improve reliability of simulation results.

Detailed image of microscopic structures and orientations of [BMIM][PF6] at graphene and vacuum interfaces are investigated by using atomistic simulations. Imidazolium rings and alkyl side chains of [BMIM] lie preferentially flat on graphene surface. At IL-vacuum interface, ionic groups pack closely together to form polar domains, leaving alkyl side chains populated at interface and imparting hydrophobic character. With the increase of IL filmthickness, orientations of [BMIM] change gradually from dominant flat distributions along graphene surface to orientations where imidazolium rings are either parallel or perpendicular to IL-vacuum interface with tilted angles. The interfacial spatial ionic structural heterogeneity formed by ionic groups also contributes to heterogeneous dynamics in interfacial regions.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2013. 82 p.
Keyword
dissipative particle dynamics, electrostatic interaction, ionic liquid, coarse-grained model
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-92707 (URN)978-91-7447-727-6 (ISBN)
Public defence
2013-09-27, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 09:30 (English)
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Available from: 2013-09-05 Created: 2013-08-15 Last updated: 2013-08-15Bibliographically approved

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