%0 Journal Article %J Journal of Physical Chemistry B %D 2007 %T Quantifying the diffusion of a fluid through membranes by double phase encoded remote detection magnetic resonance imaging %A Telkki, V. V. %A Hilty, C. %A Garcia, S. %A Harel, E. %A Pines, A. %K mri %X

We demonstrate that a position correlation magnetic resonance imaging (MRI) experiment based on two phase encoding steps separated by a delay can be used for quantifying diffusion across a membrane. This method is noninvasive, and no tracer substance or concentration gradient across the membrane is required. Because, in typical membranes, the T-1 relaxation time of the fluid spins is usually much longer than the T-2 time, we developed and implemented a new position correlation experiment based on a stimulated spin-echo, in which the relaxation attenuation of the signal is dominated by T-1 instead of T-2. This enables using relatively long delays needed in the diffusion measurements. The sensitivity of the double encoded experiment detected in a conventional way is still low because of the low filling factor of the fluid inside the NMR coil around the sample. We circumvent this problem by using the remote detection technique, which significantly increases the sensitivity, making it possible to do the measurements with gaseous fluids that have a low spin-density compared to liquids. We derive a model that enables us to extract a diffusion constant characterizing the diffusion rate through the membrane from the obtained correlation images. The double phase encoded MRI method is advantageous in any kind of diffusion studies, because the propagator of fluid molecules can directly be seen from the correlation image.

%B Journal of Physical Chemistry B %V 111 %P 13929-13936 %8 Dec 20 %@ 1520-6106 %G English %U ://WOS:000251615400011 %N 50 %M WOS:000251615400011 %! Quantifying the diffusion of a fluid through membranes by double phase encoded remote detection magnetic resonance imaging %R Doi 10.1021/Jp076760e %0 Journal Article %J Nature %D 1992 %T Quantification of the Disorder in Network-Modified Silicate-Glasses %A Farnan, I. %A Grandinetti, P. J. %A Baltisberger, J. H. %A Stebbins, J. F. %A Werner, U. %A Eastman, M. A. %A Pines, A. %K time %X

Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional O-17 dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

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