Measurement of diffusion in the presence of shear flow.

Détails

ID Serval
serval:BIB_289530ACBFCF
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
Measurement of diffusion in the presence of shear flow.
Périodique
Journal of Magnetic Resonance
Auteur(s)
Lutti A., Callaghan P.T.
ISSN
1090-7807 (Print)
ISSN-L
1090-7807
Statut éditorial
Publié
Date de publication
05/2006
Volume
180
Numéro
1
Pages
83-92
Langue
anglais
Notes
Publication types: Journal ArticlePublication Status: ppublish
Résumé
We demonstrate here a method whereby molecular diffusion coefficients may be measured in the presence of the deformational flow field of a rheo-NMR cell. The method, which uses a repetitive CPMG train of rf pulses interspersed with magnetic field gradient pulses, allows the anisotropic diffusion spectrum to be directly probed. We focus on the cylindrical Couette cell, for which the radial, tangential, and axial directions correspond to the hydrodynamic velocity gradient, velocity, and vorticity directions. While ideal Couette flow does not perturb the vorticity direction, it does perturb diffusion measurements for the velocity gradient direction, and to a lesser extent, the velocity direction. We show that with closely spaced gradient pulses operating in a flow-compensating mode, there exists a diffusion limit below which one cannot measure, that scales as T(2)gamma(4), where gamma is the shear rate and T the gradient pulse repetition period. For a typical rheo-NMR cell, and for the more challenging velocity gradient direction, diffusion rates above 10(-12) m(2) s(-1) can be accurately measured (to 1% error) at shear rates up to 3s(-1). We demonstrate the use of the method in measuring the diffusion spectrum of a lyotropic lamellar phase under shear.
Pubmed
Web of science
Création de la notice
08/07/2013 10:22
Dernière modification de la notice
20/08/2019 14:08
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