Translational and rotational motion in liquids by means of field cycling NMR

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The aim of the project is to investigate translational and rotational dynamics of viscous liquids by means of 1H and 19F spin-lattice relaxation revealed by applying field-cycling (FC) NMR. The relaxation includes two contributions: The first one is caused by fluctuations of the intramolecular dipole-dipole interactions which are associated with rotational dynamics, while the second one originates from intermolecular fluctuations mediated mainly by translational motion (diffusion). Applying modern FC NMR, which covers a frequency range of 10 kHz – 20 MHz (1H), our preparatory work shows that the inter- and intramolecular relaxation spectrum can be unambiguously separated, without a need of tedious isotope dilution. Thus, NMR relaxometry gives a unique opportunity to study translational and rotational dynamics by a single experiment. The shape of the relaxation spectra provides information about the motional mechanism, and by applying an appropriate model for the intermolecular contribution the diffusion coefficient can be extracted in a broad temperature range. This will be exploited for liquids with progressively increasing complexity concerning dynamics as well as spin properties. In addition, MD simulations will be carried out to provide a broadly applicable description of the intermolecular spectrum. The extracted rotational contribution will be compared with results from 2H NMR and dielectric spectroscopy, both probing molecular rotations. As far as the translational diffusion is concerned, we aim at establishing NMR relaxometry as a complementary method to gradient NMR.