Berlin 2008 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 11: Glasses I (joint session DF/DY)
DY 11.3: Talk
Tuesday, February 26, 2008, 10:15–10:30, EB 407
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 — •Catalin Gainaru1, Oliver Lips2, Anna Troshagina1, Robert Kahlau1, Alexander Brodin1, Franz Fujara2, and Ernst A. Rössler1 — 1Experimentalphysik II, Universität Bayreuth, D-95444 Bayreuth — 2Inst. f. Festkörperphysik, TU Darmstadt, Hochschulstraße 6, D-64289 Darmstadt
Recently we introduced a new approach to disentangle α-peak and excess wing (EW) contributions in the dielectric spectra of glass formers, assuming that the α-process obeys frequency-temperature superposition (FTS) in the full temperature range above the glass transition temperature Tg. Based on this scenario, a comparison between the orientational correlation functions of rank l=1 (probed by dielectric spectroscopy – DS) and l=2 (probed for the first time over a broad frequency range by field cycling NMR and light scattering – LS) is carried out. For the glass former glycerol DS, NMR and LS spectra are scaled according to FTS over 15 decades in frequency. Significant differences in the spectral shape of the susceptibilities of different ranks are recognized on both sides of the relaxation peak, while the time constants turn out to be the same. Regarding the systematic differences observed at high frequencies, they are explained by assuming that the fast dynamics (EW) proceeds via small angles. Below Tg, NMR and DS reflect the same dynamics down to cryogenic temperatures.