NMR determination of the physical properties of nematics

Luckhurst, G.R., Sugimura, A., Timimi, B.A. and Zimmermann, H. (2005) NMR determination of the physical properties of nematics. Liquid Crystals, 32 (11-12), 1389-1396. (doi:10.1080/02678290500124692).

Abstract

Certain physical properties of nematics can be obtained from the field-induced static and dynamic director orientations in thin films. Here we describe how deuterium nuclear magnetic resonance (NMR) spectroscopy can be used to investigate the field-induced director orientation in nematic liquid crystals. This powerful approach is illustrated with specifically deuteriated 4-pentyl-4'-cyanobiphenyl (5CB) subject to the magnetic field of the spectrometer and an electric field applied at an angle to it. A series of deuterium NMR spectra was acquired as a function of the applied electric field, which can be used to explore the static director orientation. When the electric field is applied to the nematic, the director moves from being parallel to the magnetic field to being at an angle to it (the turn-on process) because Delta epsilon and Delta chi are both positive for 5CB. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field (the turn-off process). Deuterium NMR spectra were recorded during the turn-on and the turn-off alignment processes as a function of time. Analysis of these results for the static and dynamic experiments, based on the predictions of continuum theory, provides the physical properties of the nematic.

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