AVS 66th International Symposium & Exhibition
    Chemical Analysis and Imaging Interfaces Focus Topic Wednesday Sessions
       Session CA+NS+SS+VT-WeA

Paper CA+NS+SS+VT-WeA8
Survey of Ionic Liquid Interfaces under Vacuum and Ambient Conditions: An XPS Perspective

Wednesday, October 23, 2019, 4:40 pm, Room A120-121

Session: Chemical Analysis and Imaging of Liquid/Vapor/Solid Interfaces I
Presenter: Yehia Khalifa, Ohio State University
Authors: Y. Khalifa, Ohio State University
A. Broderick, University of Delaware
J.T. Newberg, University of Delaware
Y. Zhang, University of Notre Dame
E. Maginn, University of Notre Dame
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Properties and behavior of Ionic Liquid interfaces tend to behave differently from their bulk counterparts. In this study the preferential enhancement of the lower molar concentration anion [TFSI] in a mixture of [C2MIM][OAc] and [C2MIM][TFSI] is shown in the top 17 Å via angle-resolved X-ray photoemission spectroscopy under ultra high vacuum conditions. This is supported by molecular simulations where a quantitative relationship is also established between the two techniques. This interfacial enhancement is not only unique to mixtures but is also displayed in a pure ionic liquid with a hydrophilic anion such as [HMIM][Cl] studied via ambient pressure X-ray photoemission spectroscopy. The surface of [HMIM][Cl] under vacuum and increasing pressures of water vapor was evaluated (maximum of 5 Torr, 27% relative humidity). Our quantitative results indicate a significantly larger mole fraction of water at the interface compared to the bulk with increasing pressures when compared to previously published tandem differential mobility analysis results on [HMIM][Cl] nanodroplets. Furthermore the reverse isotherms has shown that the water uptake on the interface is a reversible process. These results highlight the unique behavior of ionic liquid interfaces that can be exploited for smart materials design and application.