• Ordering in nematic liquid crystals from NMR cross-polarization studies

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      https://www.ias.ac.in/article/fulltext/pram/061/02/0249-0262

    • Keywords

       

      NMR; cross polarization; liquid crystals; dipolar couplings; ordering; order parameter

    • Abstract

       

      The measurement of dipolar couplings between nuclei is a convenient way of obtatining directly liquid crystalline ordering through NMR since the coupling is dependent on the average orientation of the dipolar vector in the magnetic field which also aligns the liquid crystal. However, measurement of the dipolar coupling between a pair of selected nuclei is beset with problems that require special solutions. In this article the use of cross polarization for measuring dipolar couplings in liquid crystals is illustrated. Transient oscillations observed during cross polarization provide the dipolar couplings between essentially isolated nearest neighbour spins which can be extracted for several sites simultaneously by employing two-dimensional NMR techniques. The use of the method for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment are considered and their utility illustrated. A method for obtaining proton-proton dipolar couplings, by utilizing cross polarization from the dipolar reservoir, is also presented.

    • Author Affiliations

       

      K V Ramanathan1 Neeraj Sinha2

      1. Sophisticated Instruments Facility, Indian Institute of Science, Bangalore - 560 012, India
      2. Department of Physics, Indian Institute of Science, Bangalore - 560 012, India
    • Dates

       
  • Pramana – Journal of Physics | News

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      Posted on July 25, 2019

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