Münster 1999 – wissenschaftliches Programm
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CP: Chemische Physik
CP 33: Poster: Dynamik molekularer Systeme
CP 33.2: Poster
Montag, 22. März 1999, 18:00–20:00, R52/R72
Measuring Diffusion Constants in Mesoporous Systems with Stray Field NMR — •E. Gedat, H.-H. Limbach, and G. Buntkowsky — FU Berlin, Institut f"ur Organische Chemie, Takustr. 3, 14195 Berlin
Translational diffusion constants of chemical compounds in various geometrical and chemical environments can be measured by NMR techniques in a magnetic field gradient. The gradient delivers the spatial resolution, and the time resolution is encoded in the pulse sequence. In general there are two ways of employing magnetic field gradients. Either NMR probes can be employed that allow pulsed gradients, or one can use the gradient of the stray field below the homogeneous area of the magnet. Following the latter, we have constructed and build a stray field NMR setup that can be mounted on common magnets and probes. It provides an accuracy of at least 50 µm vertical displacement. A field calibration of the magnetic stray field of the Bruker MSL 7T superconducting magnet was performed in the field region of ≈ 2.85 T, where a conventional 31P tuned X-nucleus probe of the MSL can be employed for the diffusion measurements. In this region the gradient strength has a maximum and is highly linear, as can be seen from the magnetic field profile plot. A magnetic field gradient value of 38.1 T/m was found. This setup was tested with H2O at fields of 6.93 T (295.00 MHz) and PDMS (Polydimethylsiloxane) at 2.85 T (121.49 MHz). Diffusion coefficient measurements of bulk liquids as well as of guest molecules in restricted geometries are presented.