| On the nature of the high-frequency relaxation in a molecular glass former: a joint study of glycerol by field cycling NMR, dielectric spectroscopy, and light scattering. | |
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MedLine Citation:
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PMID: 18465928 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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Fast field cycling (1)H NMR relaxometry is applied to determine the dispersion of spin-lattice relaxation time T(1)(omega) of the glass former glycerol in broad temperature (75-360 K) and frequency (10 kHz-30 MHz) ranges. The relaxation data are analyzed in terms of a susceptibility chi(")(omega) proportional, variantomegaT(1)(omega), related to the second rank (l=2) molecular orientational correlation function. Broadband dielectric spectroscopic results suggest the validity of frequency temperature superposition above the glass transition temperature T(g). This allows to combine NMR data of different temperatures into a single master curve chi(")(omegatau(alpha)) that extends over 15 decades in reduced frequency omegatau(alpha), where tau(alpha) is the structural alpha-relaxation time. This master curve is compared with the corresponding ones from dielectric spectroscopy (l=1) and depolarized light scattering (l=2). At omegatau(alpha)<1, NMR susceptibility is significantly different from both the dielectric and light scattering results. At omegatau(alpha)>1, there rather appears a difference between the susceptibilities of rank l=1 and l=2. Specifically, at omegatau(alpha)>>1, where the susceptibility is dominated by the so-called excess wing, the NMR and light scattering spectra (both l=2) rather coincide with each other and are about three times more intense than the dielectric (l=1) spectrum. This is explained by assuming that the high frequency dynamics correspond to only small-angle excursions. Below T(g), dielectric and NMR susceptibility compare well and exhibit an exponential temperature dependence. |
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Authors:
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C Gainaru; O Lips; A Troshagina; R Kahlau; A Brodin; F Fujara; E A Rössler |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The Journal of chemical physics Volume: 128 ISSN: 0021-9606 ISO Abbreviation: J Chem Phys Publication Date: 2008 May |
Date Detail:
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Created Date: 2008-05-09 Completed Date: 2008-07-21 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0375360 Medline TA: J Chem Phys Country: United States |
Other Details:
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Languages: eng Pagination: 174505 Citation Subset: - |
Affiliation:
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Experimentalphysik II, Universität Bayreuth, D-95 444 Bayreuth, Germany. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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