Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of
molecular diffusion paths (notably, the probability distribution of molecular displacements over
typically micrometers, covered during an observation time of typically milliseconds) and has thus
proven to serve as a most versatile means for the in-depth study of mass transfer in complex materials.
This is particularly true with nanoporous host materials, where PFG NMR enabled the first direct
measurement of intracrystalline diffusivities of guest molecules. Spatial resolution, i.e., the minimum
diffusion path length experimentally observable, is limited by the time interval over which the pulsed
field gradients may be applied. In “conventional” PFG NMR measurements, this time interval is
determined by a characteristic quantity of the host-guest system under study, the so-called transverse
nuclear magnetic relaxation time. This leads, notably when considering systems with low molecular
mobilities, to severe restrictions in the applicability of PFG NMR. These restrictions may partially be
released by performing PFG NMR measurements in combination with “magic-angle spinning” (MAS)
of the NMR sample tube. The present review introduces the fundamentals of this technique and
illustrates, via a number of recent cases, the gain in information thus attainable. Examples include
diffusion measurements with nanoporous host-guest systems of low intrinsic mobility and selective
diffusion measurement in multicomponent systems.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:84603 |
| Date | 06 April 2023 |
| Creators | Kärger, Jörg, Freude, Dieter, Haase, Jürgen |
| Publisher | MDPI |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:article, info:eu-repo/semantics/article, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 2227-9717, 147 |
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