Molecular Dynamics in Nematic Phases: QENS and NMR Spectroscopy

  • M. Riccò
  • M. P. Fontana
Part of the NATO ASI Series book series (NSSB, volume 290)


Molecular dynamics in liquid crystals (particularly smectic and to a lesser extent nematic phases) has been extensively studied by quasi elastic neutron scattering (QENS)1-11 as well as by magnetic relaxation12–17. Nevertheless, these two different techniques have never been combined, probably due to the fact that, quite often, the results obtained did not agree. The situation is particularly difficult in the nematic phase, where translational and rotational time scales are not well separated. There is, however, much interest in this type of combined study, since it is by coupled measurements that we may have a chance to unravel the complexities of the dynamics in these interesting materials. Furthermore, the extensive work on reorientational dynamics performed by Raman and Infrared fluctuation spectroscopy (see Chapter 19) showed several intriguing anomalies: the decrease of the spinning diffusion coefficient (for rotations about the main molecular axis) with increasing temperature, the large discrepancy between the temperature behavior and values of the tumbling diffusion coefficient (for rotations of the main molecular axis) determined with IR and Raman spectroscopy and those found with fluorescence depolarization spectroscopy. Thus it is important to use QENS, which directly probes the motions of atomic nuclei, and 13C NMR, which is directly sensitive to molecular reorientations, to resolve these discrepancies and thus to gain finally a quantitative picture of molecular dynamics in such complex fluids.


Liquid Crystal Nematic Phase Rotational Diffusion Spin Lattice Relaxation Time Nematic Director 
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Copyright information

© Springer Science+Business Media New York 1992

Authors and Affiliations

  • M. Riccò
    • 1
  • M. P. Fontana
    • 1
  1. 1.Dipartimento di FisicaUniversità di ParmaParmaItaly

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