A practical tutorial to set up NMR diffusometry equipment: application to liquid crystals

Abstract

NMR diffusometry is nowadays a well-established and powerful technique to investigate molecular translation in fluid materials. Standard NMR diffusometry approaches are based on pulsed field gradients generated by specific hardware and specially designed NMR probes. Here, we present an alternative set-up that exploits the static gradient present in the fringe field of any commercial superconducting magnet. This stray field diffusometry technique can be particularly useful to study diffusional processes in fast-relaxing and slow-diffusing systems, such as thermotropic liquid crystals, ionic liquids and polymer melts.

Nuclear magnetic resonance studies of translational diffusion in thermotropic ionic liquid crystals

“…The anisotropic spin interactions in LCs lead to spectral splitting and line-broadening as well as correspondingly quick decays of spin coherences. The signal loss due to spin-spin relaxation process, limits the gradient encoding/decoding times (gradient pulse length δ in Figure 1), and thereby places a lower limit on the assessable diffusion coefficients [20].…”

“…To achieve sufficient spin-coherence diffusional dephasing, stronger field gradients can be used as an alternative to the suppression of line broadening. Experiments on LCs have been performed using large static gradients in the stray field of conventional superconducting NMR magnets [20,31,32]. The experimental pulse sequence is as in Figure 1, but with the field gradient field constantly present.…”