期刊
ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS
卷 226, 期 11-12, 页码 1149-1168出版社
OLDENBOURG VERLAG
DOI: 10.1524/zpch.2012.0281
关键词
Solid State P-31 NMR; Reorientation Dynamics; Relaxation Processes; Molecular Glass Formers
资金
- Deutsche Forschungsgemeinschaft (DFG) [RO 907/10-1]
We study molecular reorientation in the glass formers triethyl-, tripropyl-, and m-tricresyl phosphate by measuring P-31 NMR spectra, relaxation (T-1 and T-2), stimulated echo decays and two-dimensional spectra over a large temperature range (130-370 K). The results are compared to those from dielectric spectroscopy (DS) and depolarized light scattering (LS). While the time constants tau(alpha) of the primary (alpha-) process in the range 10(-11)-100 s well agree, the stretching of the reorientational correlation function is probe dependent, i.e., the rank-two functions (NMR and LS) essentially agree whereas the rank-one function (DS) is less stretched. The very similar 2D spectra recorded as a function of mixing time demonstrate that the reorientational mechanism does not significantly vary among the super-cooled liquids. A model of combining large- and small-angle reorientation allows for reproducing the 2D spectra and may be taken as generic for the dynamics in viscous molecular liquids. Pronounced secondary (beta-) processes do not only effect the NMR relaxation but can be identified directly in the time domain by the stimulated echo technique. This becomes possible due to its broad time window (10 mu s-100 s). Thus, applying the different 1D and 2D techniques makes P-31 NMR well suited to probe molecular reorientation over a wide dynamic range.
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