Vacuum Interfacial Structure and X‑ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective

Waruni V. Karunaratne; Man Zhao; Edward W. Castner; Claudio J. Margulis

doi:10.1021/acs.jpcc.2c03311

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Vacuum Interfacial Structure and X‑ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective

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Vacuum Interfacial Structure and X‑ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective

Waruni V. Karunaratne, Man Zhao, Edward W. Castner and Claudio J. Margulis

Journal of physical chemistry. C, Vol.126(32), pp.13936-13945

08/18/2022

DOI: 10.1021/acs.jpcc.2c03311

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Abstract

We report studies of the vacuum interfacial structure of a series of 1-methyl-3-alkylimidazolium bis(perfluoroalkanesulfonyl)imide ionic liquids (ILs) and predict and explain their Fresnel-normalized X-ray reflectivity. To better interpret the results, we use a theory we recently developed dubbed “the peaks and antipeaks analysis of reflectivity” which splits the overall signal into that of different pair subcomponents. Whereas the overall reflectivity signal is not very informative, the peak and trough intensities for the pair subcomponents provide rich information for analysis. When species containing cationic alkyl or anionic fluoroalkyl tails are present at the interface, a tail layer is found next to a vacuum, and this tail layer can be composed of both alkyl and fluoroalkyl moieties. To maintain the positive–negative alternation of charged groups, alkyl and fluoroalkyl tails must necessarily be nearby and cannot segregate. Charged groups are found in the subsequent layer just below the interface and arranged to achieve lateral charge neutrality. In general, fluctuations at and away from the interface are based on polarity (i.e., heads and tails) and not on charge; when there are no significant alkyl or fluoroalkyl moieties in the IL, atomic density fluctuations away from the interface are small and appear to exist for the purpose of achieving lateral charge balance. For all the systems reported here, the persistence length of density fluctuations does not go beyond ∼7 nm.

C: Physical Properties of Materials and Interfaces

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Title: Subtitle: Vacuum Interfacial Structure and X‑ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective
Creators: Waruni V. Karunaratne - University of Iowa
Man Zhao - Rutgers, The State University of New Jersey
Edward W. Castner - Rutgers, The State University of New Jersey
Claudio J. Margulis - University of Iowa
Resource Type: Journal article
Publication Details: Journal of physical chemistry. C, Vol.126(32), pp.13936-13945
DOI: 10.1021/acs.jpcc.2c03311
ISSN: 1932-7447
eISSN: 1932-7455
Publisher: American Chemical Society
Grant note: DOI: 10.13039/100000165, name: Division of Chemistry, award: CHE-1954358, CHE-1954809
Language: English
Date published: 08/18/2022
Academic Unit: Chemistry
Record Identifier: 9984284548002771

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