Anion Enhancement at the Liquid Vacuum Interface of an Ionic Liquid Mixture

Y Zhang and Y Khalifa and EJ Maginn and JT Newberg, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 27392-27401 (2018).

DOI: 10.1021/acs.jpcc.8b07995

The liquid vacuum interface was investigated for a ionic liquid (IL) mixture containing 1-ethyl-3-methylimidazolium acetate, C2MIM OAc, and 1ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, C2MIM TFSI. Herein, we detail a quantitative connection between molecular simulations and angle-resolved X-ray photoemission spectroscopy for an IL vacuum interface. Results show that for a mixture with a low concentration of TFSI(-), the anion OAc(-) is slightly depleted from the interface, whereas the TFSI(-) anion is significantly enhanced relative to the bulk. Both experiments and simulations reveal that the mole fraction of TFSI(-) increases significantly from the bulk value in the top 17 angstrom. Furthermore, simulations show that TFSI(-) has a preferred orientation at the liquid-vacuum interface.

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