Translational and rotational diffusion of glycerol by means of field cycling 1H NMR relaxometry.
Field cycling (FC) (1)H NMR relaxometry has been applied to study translational and rotational dynamics of nondeuterated (-h(8)) and partially deuterated (-h(3) and -h(5)) glycerol in a broad temperature range. 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 (1)H-(1)H as well as (1)H-(2)H 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 (1)H NMR. Moreover, the approach allows extracting the diffusion coefficient D, which is in good agreement with results from gradient (1)H NMR. Thus, (1)H NMR relaxometry has the potential to become an alternative method for measuring the diffusion coefficient in viscous liquids.
Experimentalphysik II, Universität Bayreuth, Bayreuth, Germany.
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Meier
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Rössler