Regensburg 2010 – wissenschaftliches Programm

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SYMR: Symposium Nuclear Magnetic Resonance: from Applications in Condensed-Matter Physics to New Frontiers

SYMR 8: Glasses and Glass Transition

SYMR 8.10: Vortrag

Mittwoch, 24. März 2010, 17:00–17:15, H48

Low-Frequency Excess Contribution in Simple Liquids Revealed by Fast Field Cycling NMR — •Roman Meier, Axel Herrmann, Robert Kahlau, Danuta Kruk, and Ernst Rössler — Experimentalphysik II, Universität Bayreuth, Germany

The main relaxation (α-relaxation) of simple liquids studied by dielectric spectroscopy is well described by a Cole-Davidson (CD) susceptibility. In particular the low-frequency limit follows a Debye behavior χDS∝ ω1. Applying fast field cycling (FFC) 1H NMR and transforming the spin-lattice dispersion data T1 into the susceptibility representation χNMR ∝ ν/T1 we have discovered a low-frequency excess contribution for systems like glycerol and its homologues as well as fluoroaniline. The CD function fails to describe the data due to a retarded transition to the limit ω1, i.e., a “shoulder” is observed on the low frequency side of the a-relaxation peak (ω τα <1) possibly reflecting a slower relaxation process. Actually only a few liquids like o-terphenyl and tristyrene studied by FFC NMR do not show this phenomenon. Collecting dispersion data over a large temperature range, the relaxation strength of the excess contribution is specified quantitatively. Measurements of dilution series of propylene glycol in deuterated chloroform proved an intermolecular origin of the excess contribution. Dilution experiments of deuterated in protonated glycerol suggest this additional contribution being also fully reflected by sole intramolecular spin-spin vectors. A possible explanation of this effect are transient molecular clusters due to chemical interactions (e.g. H-bonds).

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