title: Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry.
abstract: Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(ω) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.
authors.affiliation: Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, Słoneczna 54, PL-10710 Olsztyn, Poland.
authors.forename: D
authors.initials: D
authors.lastname: Kruk
authors.affiliation: Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Meier
authors.affiliation: Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Rachocki
authors.affiliation: Department of Biophysics, Jagiellonian University Medical College, Łazarza 16, 31-530 Kraków, Poland and Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Korpała
authors.affiliation: Ionic Liquid and Solid State Ionics Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221 005, India.
authors.forename: R K
authors.initials: RK
authors.lastname: Singh
authors.affiliation: Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth, Germany.
authors.forename: E A
authors.initials: EA
authors.lastname: Rössler
mesh_terms: D004058:Diffusion; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D013816:Thermodynamics
chemical_list: C412621:1-butyl-3-methylimidazolium hexafluorophosphate; C419324:1-butyl-3-methylimidazolium tetrafluoroborate; D007093:Imidazoles; D052578:Ionic Liquids; C518739:1-ethyl-3-methylimidazolium