Surface layering and melting in an ionic liquid studied by resonant soft X-ray reflectivity

The molecular-scale structure of the ionic liquid [C ₁₈mim] ⁺[FAP] ⁻ near its free surface was studied by complementary methods. X-ray absorption spectroscopy and resonant soft X-ray reflectivity revealed a depth-decaying near-surface layering. Element-specific interfacial profiles were extracted wi...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2013-03, Vol.110 (10), p.3733-3737
Main Authors: Mezger, Markus, Ocko, Benjamin M., Reichert, Harald, Deutsch, Moshe
Format: Article
Language:English
Subjects:
Anions
Electron density
Fluorine
Infrared reflection
Ionic liquids
Melting
Molecules
Physical Sciences
Reflectance
Resonance
Resonance scattering
Surface temperature
Temperature
X-rays
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Summary:The molecular-scale structure of the ionic liquid [C ₁₈mim] ⁺[FAP] ⁻ near its free surface was studied by complementary methods. X-ray absorption spectroscopy and resonant soft X-ray reflectivity revealed a depth-decaying near-surface layering. Element-specific interfacial profiles were extracted with submolecular resolution from energy-dependent soft X-ray reflectivity data. Temperature-dependent hard X-ray reflectivity, small- and wide-angle X-ray scattering, and infrared spectroscopy uncovered an intriguing melting mechanism for the layered region, where alkyl chain melting drove a negative thermal expansion of the surface layer spacing.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1211749110