Journal
CHEMPHYSCHEM
Volume 14, Issue 13, Pages 3071-3081Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201300257
Keywords
diffusion; liquids; molecular dynamics; NMR spectroscopy; polymers
Funding
- Deutsche Forschungsgemeinschaft [RO 907/15, RO 907/16, FU 308/14]
- Polish Ministry of Science and Education [NN202 105936]
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With the advent of commercial field-cycling (FC) spectrometers, NMR relaxometry has gained new momentum as a method of investigating dynamics in liquids and polymers. The outcome of FC NMR experiments is spin-lattice relaxation time versus frequency (relaxation dispersion). In the case of protons, due to the intra- and intermolecular origin of dipolar interactions, the relaxation dispersion reflects rotational as well as translational dynamics. The latter shows a universal dispersion law at low frequencies, which allows determination of the diffusion coefficient D(T) in addition to the rotational correlation time (rot)(T), that is, FC H-1 NMR becomes an alternative to field-gradient NMR spectroscopy. Subdiffusive translation found in polymers can be accessed by singling out the intermolecular relaxation through isotope dilution experiments, and the mean square displacement can then be revealed as a function of time, thus complementing neutron scattering experiments. Likewise, information on reorientational dynamics is provided by the intramolecular relaxation. Assuming frequency-temperature superposition the corresponding correlation functions can be monitored up to eight decades in amplitude and time, which allows thorough testing of current polymer theories.
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