Abstract
Hypothesis: Room Temperature Ionic Liquids (RTILs) bulk's molecular layering dominates their structure also at the RTIL/sapphire interface, increasing the layer spacing with the cationic alkyl chain length n. However, the negatively-charged sapphire surface compresses the layers, increases the layering range, and affects the intra-layer structure in yet unknown ways. Experiments: X-ray reflectivity (XR) off the RTIL/sapphire interface, for a broad homologous RTIL series 1-alkyl-3-methylimidazolium bis(trifluoromethansulfonyl)imide, hitherto unavailable for any RTIL. Findings: RTIL layers against the sapphire, exhibit two spacings: da and db. da is n-varying, follows the behavior of the bulk spacing but exhibits a downshift, thus showing significant layer compression, and over twofold polar slab thinning. The latter suggests exclusion of anions from the interfacial region due to the negative sapphire charging by x-ray-released electrons. The layering range is larger than the bulk's. db is short and near n-independent, suggesting polar moieties' layering, the coexistence mode of which with the da-spaced layering is unclear. Comparing the present layering with the bulk's and the RTIL/air interface's provides insight into the Coulomb and dispersion interaction balance dominating the RTIL's structure and the impact thereon of the presence of a charged solid interface.
Original language | English |
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Pages (from-to) | 33-45 |
Number of pages | 13 |
Journal | Journal of Colloid and Interface Science |
Volume | 661 |
DOIs | |
State | Published - May 2024 |
Bibliographical note
Publisher Copyright:© 2024 Elsevier Inc.
Funding
We thank ESRF for beamtime at ID15A, ESRF's Partnership for Soft Condensed Matter (PSCM) for support, and Dr. T. Buslaps (ESRF) for assistance and advice. We also thank PETRA-III for beamtime at LISA (funded by BMBF ErUM-Pro grants 05K16FK1 and 05K19FK3 ), and Drs. Sven Festersen and Benjamin Runge (Kiel University, Germany) for assistance and discussions. Contributions by Dr. Julia Haddad (Physics Dept., Bar-Ilan University, Israel) and Dr. Ben Ocko (NSLS-II, Brookhaven National Laboratory, USA) to this study in experiments, analysis, and discussions are gratefully acknowledged. We thank ESRF for beamtime at ID15A, ESRF's Partnership for Soft Condensed Matter (PSCM) for support, and Dr. T. Buslaps (ESRF) for assistance and advice. We also thank PETRA-III for beamtime at LISA (funded by BMBF ErUM-Pro grants 05K16FK1 and 05K19FK3), and Drs. Sven Festersen and Benjamin Runge (Kiel University, Germany) for assistance and discussions. Contributions by Dr. Julia Haddad (Physics Dept. Bar-Ilan University, Israel) and Dr. Ben Ocko (NSLS-II, Brookhaven National Laboratory, USA) to this study in experiments, analysis, and discussions are gratefully acknowledged.
Funders | Funder number |
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Physics Dept. Bar-Ilan University | |
Brookhaven National Laboratory | |
European Synchrotron Radiation Facility | |
Bundesministerium für Bildung und Forschung | 05K16FK1, 05K19FK3 |