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NMR Experiments on Molecular Dynamics in Nanoporous Media: Evidence for Lévy Walk Statistics

Published online by Cambridge University Press:  10 February 2011

Rainer Kimmich ,
Tatiana Zavada  and
Siegfried Stapf
Rainer Kimmich
Affiliation:
Universität Ulm, Sektion Kernresonanzspektroskopie, 89069 Ulm, Germany
Tatiana Zavada
Affiliation:
Universität Ulm, Sektion Kernresonanzspektroskopie, 89069 Ulm, Germany
Siegfried Stapf
Affiliation:
Universität Ulm, Sektion Kernresonanzspektroskopie, 89069 Ulm, Germany
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Abstract

Field-cycling 1H and 2H NMR relaxometry and field-gradient 1H NMR diffusometry were applied to polar and nonpolar liquids filled into porous glasses and fineparticle agglomerates (SiO2, ZnO, TiO2, globular proteins). The orders of magnitude of the length scales of the pore spaces ranged from 100 to several 102 nm. Pronounced differences of the spin-lattice relaxation dispersion for “weak” (nonpolar) and “strong” (polar) adsorption were found. In the latter case, the correlation times of the adsorbate orientation are up to eight orders of magnitude longer than in bulk. Trans-lational diffusion in liquid surface layers was directly studied with the aid of field-gradient NMR diffusometry in systems where the free liquid was frozen. The spin-lattice relaxation dispersion can be explained on the basis of reorientations mediated by translational displacements (RMTD) of adsorbate molecules on the surfaces. Thisprocess appears to be enhanced by a Levy walk mechanism so that the propagator adopts the form of a Cauchy distribution. The evaluated surface correlation functions are characterized by surface correlation lengths in the same order as the pore diameters, that is, up to three orders ofmagnitude larger than the length scale of dipolar interaction.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 464: Symposium FF – Dynamics in Small Confining Systems III , 1996 , 313
Copyright
Copyright © Materials Research Society 1997

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References

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