Solid-liquid interfaces of ionic liquid solutions--Interfacial layering and bulk correlations.
The influence of the polar, aprotic solvent propylene carbonate on the interfacial structure of the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate on sapphire was investigated by high-energy x-ray reflectivity. Experiments at solvent concentrations between 17 mol. % and 83 mol. % bridge the gap between diluted electrolytes described by the classical Gouy-Chapman theory and pure ionic liquids. Analysis of our experimental data revealed interfacial profiles comprised of alternating anion and cation enriched regions decaying gradually into the bulk liquid. With increasing solvent concentration, we observed a decrease in correlation length of the interfacial layering structure. At high ion concentrations, solvent molecules were found to accumulate laterally within the layers. By separating like-charged ions, they reduce their Coulomb repulsion. The results are compared with the bulk structure of IL/solvent blends probed by x-ray scattering and predictions from fundamental fluid theory.
Institute of Physics, Johannes Gutenberg University Mainz, 55128 Mainz, Germany.
Markus
M
Mezger
Institute for Theoretical Physics, Eberhard Karls Universität Tübingen, 72076 Tübingen, Germany.
Roland
R
Roth
Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
Heiko
H
Schröder
Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
Peter
P
Reichert
European Synchrotron Radiation Facility, 38043 Grenoble, France.
Diego
D
Pontoni
European Synchrotron Radiation Facility, 38043 Grenoble, France.
Harald
H
Reichert