Surface and Interface Science

0519407 - ÚCHP 2021 RIV DE eng M - Monography Chapter
Nakajima, K. - Lísal, Martin - Kimura, K.
Surfaces of Ionic Liquids.
Surface and Interface Science. Volume 7. Weinheim: Wiley-VCH Verlag GmbH, 2020, s. 351-389. ISBN 978-3-527-41159-7
Institutional support: RVO:67985858
Keywords : ionic liquids * MD simulations * binary mixtures
OECD category: Physical chemistry

In this contribution, the results of HR-RBS studies on the surface structures of typical ionic liquids, i.e. imidazolium based ionic liquids, and their binary mixtures are reviewed. Not only the surface composition but also the orientation of molecules can be derived using HR-RBS. For the pure ionic liquids studied so far, the HR-RBS measurements show a universal surface structure: (1) there is no surface enrichment of either cation or anion, (2) the polar parts of cations and anions are located at almost the same depth in the subsurface region, and (3) nonpolar parts of cations and anions are pointing toward the vacuum. These results are in good agreement with the observations by other surface analysis techniques and also with the results of MD simulations. For the mixtures of ionic liquids, there is a general tendency that the surface is slightly enriched by larger ionic liquids. The observed surface enrichment can be explained rather well by the simple thermodynamic calculation based on the Sprow-Prausnitz equation with assumption of ideal solution although the deviation from the simple calculation becomes larger with increasing the ratio of the molar surface areas of the component ionic liquids. This deviation can be qualitatively explained by the nonideality of the mixture. There are apparent discrepancies in the observed surface enrichment between HR-RBS and some other surface analysis techniques, namely TOF-SIMS, LEIS and XPS. These discrepancies are attributed to the difference in the probing depth between different techniques. Considering such a difference, more detailed information of the surface structure can be obtained by combination analysis with other complemental techniques.

Permanent Link: http://hdl.handle.net/11104/0304449