Translational and Rotational Diffusion of Glycerol by Means of Field Cycling 1H NMR Relaxometry

Field cycling (FC) H-1 NMR relaxometry has been applied to study translational and rotational dynamics of nondeuterated (-h(8)) and partially deuterated (-h(3) and -h(s)) glycerol in a broad temperaturerange. We demonstrate that a low-frequency excess intensity observed in the relaxation dispersion stems from intermolecular dipole dipole interactions mediated by translational dynamics, whereas the main relaxation is attributed to rotational dynamics. A theoretical description of the relaxation processes is formulated accounting for H-1-H-1 as well as H-1-H-2 relaxation channels for the partially deuterated systems. While the intermolecular spectral density is derived from the force-free-hard-sphere model (Fick diffusion with appropriate boundary conditions) of translational motion, the intramolecular relaxation contribution is described by a Cole-Davidson spectral density. This ansatz reproduces very well the dispersion profiles obtained from FC H-1 NMR Moreover, the approach allows extracting the diffusion coefficient D, which is in good agreement with results from gradient H-1 NMR. Thus, H-1 NMR relaxometry has the, potential to become an alternative method for measuring the diffusion coefficient in viscous liquids.