Probing the structure of porous media using NMR spin echoes

Sen, P. N., Schwartz, L. M., Mitra, P. P. (1994) Probing the structure of porous media using NMR spin echoes. Magnetic Resonance Imaging, 12 (2). pp. 227-230. ISSN 0730-725X

URL: https://www.ncbi.nlm.nih.gov/pubmed/8170306
DOI: 10.1016/0730-725x(94)91523-7

Abstract

The NMR pulsed field gradient spin-echo (PFGSE) amplitude M(k,t) is a direct measure of the diffusion propagator of the molecules of a fluid diffusing in the pores of a porous medium. For small values of k = γgδ, where g is the gradient strength, δ is the duration of the gradient pulse, and γ the gyromagnetic ratio, the PFGSE amplitude gives the diffusion coefficient D(t). The exact short-time diffusion coefficient, D(t)Do=1−(4DotS/(9Vpπ)−DotHS/(12Vp)+ptS/6Vp, provides an important method for determining the surface to pore-volume ratio SVp. Here the mean surface curvature H = 〈1R1 + 1R2〉. Combining early D(t) with the magnetization decay one obtains the surface relaxivity ϱ. The long-time effective diffusion constant derived from PFGSE gives information on the tortuosity of the connected space. The diffusion coefficient measured by PFGSE equals that derived from electrical conductivity only when ϱ = 0. Exact solutions with partially absorbing boundary conditions for a periodic structure are used to illustrate the influence of ϱ on the diffusion coefficient. M(k,t) can be well represented by a convolution of the structure factor of the connected pore space with an appropriate Gaussian propagator. This ansatz provides a model-independent way of obtaining the structure factor.

Item Type: Paper
Uncontrolled Keywords: Restricted diffusion Porous medium NMR surface relaxation NMR pulsed field gradient Surfaceto-volume ratio Formation factor
Subjects: physics > biophysics
physics > fluid dynamics
Investigative techniques and equipment > magnetic resonance imaging
physics
CSHL Authors:
Communities: CSHL labs > Mitra lab
Depositing User: CSHL Librarian
Date: 1994
Date Deposited: 02 Apr 2012 20:31
Last Modified: 10 Feb 2017 20:36
Related URLs:
URI: http://repository.cshl.edu/id/eprint/25878

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