Berlin 2012 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 30: New Perspectives of Scattering at Soft Matter
CPP 30.8: Talk
Wednesday, March 28, 2012, 17:30–17:45, C 264
Resonant Soft X-Ray Reflectivity - A tool to study the near-surface structure of complex liquids — •Markus Mezger1, Benjamin Ocko2, Harald Reichert3, and Moshe Deutsch4 — 1Max-Planck-Institut für Polymerforschung, Mainz — 2Brookhaven National Laboratory, Upton NY, USA — 3European Synchrotron Radiation Facility, Grenoble, France — 4Bar-Ilan University, Ramat-Gan, Israel
X-ray reflectivity (XRR) became one of the leading techniques to study the near-surface structures of liquids. However, standard XRR is not atom-specific and can determine only surface-normal total electron density profiles. In complex liquids, this generally leads to ambiguities in the assignment of molecular moieties to reconstructed interfacial profiles. Resonant x-ray scattering techniques can overcome this limitation by enhancing and modulating the scattering contrast between different molecular moieties.
We present the first fluorine K-edge resonant soft-XRR study of the surface structure of a complex fluid, the ionic liquid [C18mim]+[FAP]−. Analysis of the x-ray absorption spectroscopy and resonant XRR data reveal a depth-decaying near-surface layering. The contributions of specific molecular moieties was unambiguously determined with sub-molecular resolution. Temperature-dependent XRR, SAXS, and FTIR uncover an intriguing melting mechanism for the layered region, where alkyl chain melting drives a negative thermal expansion of the surface layer spacing that has hitherto never been observed for an isotropic liquid.