DEUTERON RELAXATION AND ANISOTROPIC REORIENTATION OF A NEMATIC LIQUID-CRYSTAL

H-2-NMR relaxation experiments have been used to investigate molecular motion of the nematogen 2-fluorenyl-4'-tetradecycloxy benzoate-d9 (FLOC14-d9). The molecule is perdeuterated in the rigid fluorenyl moiety and in the magnetically oriented nematic phase gives spectra with seven quadrupole doublets. An inversion recovery experiment was used to measure Zeeman order relaxation times T1Z, and a separate broadband Jeener-Broekaert experiment was used to measure quadrupolar relaxation times T1Q. This combination yields spectral densities, J1i(omega-0) and J2i(2-omega-0), for each site i, on the liquid crystal molecule. The spectral density data have been interpreted by fitting the experimental results with a composite diffusion model of molecular motion of nematic liquid crystal molecules. The temperature and frequency dependence of the rotational correlation times is examined and discussed. The rotational motion is found to be statistically correlated with fluctuations of the nematic director, in such a fashion that director fluctuations make negligible contribution to the observed spectral densities.