title: Mesoscopic Correlation Functions in Heterogeneous Ionic Liquids.
abstract: A common feature of ionic liquids composed of cations with long aliphatic side chains is structural heterogeneities on the nanometer length scale. This so-called microphase separation arises from the clustering of aliphatic moieties. The temperature dependence of the liquid bulk structure was studied by small-angle X-ray and neutron scattering for a set of methylimidazolium ([C18C1im]+, [C22C1im]+) based ionic liquids with tris(pentafluoroethyl)trifluorophosphate ([FAP]-), bis(trifluoromethylsulfonyl)imide ([NTf2]-), and bis(nonafluorobutylsulfonyl)imide ([NNf2]-) anions. The experimental data is quantitatively analyzed using a generalized Teubner-Strey model. Discussion of the resulting periodicity d and correlation length ξ shows that the structural heterogeneities are governed by the interplay between the alkyl chain length, the geometry of the anion, and entropic effects. Connections between the mesoscopic correlation functions, density, and entropy of fusion are discussed in comparison to alcohols. The observed dependencies allow predictions on the mesoscopic correlation functions based on macroscopic bulk quantities.
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Weiss
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.|Institute of Physics, Johannes Gutenberg University Mainz , 55128 Mainz, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Mars
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Hailong
authors.initials: H
authors.lastname: Li
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Kircher
authors.affiliation: Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH , Lichtenbergstr. 1, 85748 Garching, Germany.
authors.forename: Oxana
authors.initials: O
authors.lastname: Ivanova
authors.affiliation: Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH , Lichtenbergstr. 1, 85748 Garching, Germany.
authors.forename: Artem
authors.initials: A
authors.lastname: Feoktystov
authors.affiliation: Max Planck Institute for Solid State Research , Outstation at Heinz Maier-Leibnitz Zentrum, Lichtenbergstr. 1, 85747 Garching, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Soltwedel
authors.affiliation: Max Planck Institute for Intelligent Systems , Heisenbergstr. 3, 70569 Stuttgart, Germany.|Institute for Theoretical Physics IV, University of Stuttgart , Pfaffenwaldring 57, 70569 Stuttgart, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Bier
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.|Institute of Physics, Johannes Gutenberg University Mainz , 55128 Mainz, Germany.
authors.forename: Markus
authors.identifier: 0000-0001-9049-6983
authors.initials: M
authors.lastname: Mezger