Recent Experimental Investigations in Nematic and Cholesteric Mesophases

  • Orsay Liquid Crystal Group


The development of the Frank thermodynamical description of liquid crystals has recently allowed quantitative predictions on the static and dynamical behavior of the nematic and cholesteric mesophases. We report here the results of our experimental investigations to measure the parameters introduced by the theory, in two main directions: (a) the magnetically induced cholesteric to nematic phase transition, in low concentration mixtures of cholesteryl esters in nematic materials, appears as a general method for measuring the “twist” elastic constant of the nematic solvent; (b) the study of the thermal fluctuations of anisotropy in nematic materials, observed by high resolution spectral analysis of the Rayleigh light scattered by the liquid crystal, allows the determination of the Leslie viscosity coefficients. Finally, we report on the observation of a new type of disclination line in cholesteric mesophases (double disclination line).

This paper is a short review of the experimental work performed during the current year by the Orsay Liquid Crystal Group on the physical properties of liquid crystal mesophases. The aim of this effort has been to test recent theoretical predictions concerning some elastic, magnetic and optical properties of liquid crystals, in the frame work of the continuum thermodynamical model. Our results have been partially published in form of letters, and experimental details can be found therin. We would like to emphasize here that the continuum model of liquid crystals is not a formal speculation; it can indeed lead to an accurate characterization of the physical behavior of the mesophases, and it gives powerful methods for the measurement of the anisotropic physical constants involved in elastic and hydrodynamical properties of liquid crystals.

We first describe an experiment of magneto-elasticity, which allows the determination of the “twist” elastic constant(1) of a nematic material. We then report on results concerning the damping of thermal fluctuations of anisotropy in a nematic mesophase, which give at the present time 4 out of the 5 Leslie viscosity coefficients(2). Finally, we describe a new type of defect (“disclination”) line recently observed in cholesteric mesophases.


Liquid Crystal Nematic Liquid Crystal Disclination Line Thickness Increment Recent Experimental Investigation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    F.C.Frank, Discuss.Faraday Soc. 25, 19 (1958)CrossRefGoogle Scholar
  2. 2.
    F.M.Leslie, Quant.Journ.Mech. and Appt Math. 19, 337 (1966)Google Scholar
  3. 3.
    E.S.Sackmann, S.Meiboom, L.C.Snyder, J.Am.Chem.Soc. 89, 5891 (1967)Google Scholar
  4. 4.
    P.G. de Gennes, Sol.State Com. 6, 163 (1968)CrossRefGoogle Scholar
  5. 5.
    R.B.Meyer, Appl.Phys.Let. 12, 281 (1968) 14, 208 (1969)CrossRefGoogle Scholar
  6. 6.
    G.Durand, L.Léger, F.Rondelez, M.Veyssié, Phys.Rev. Let. 22, 227 (1969)CrossRefGoogle Scholar
  7. 7.
    R.Cano, Bull.Soc.Franç.Mineral. 91, 20 (1968)Google Scholar
  8. 8.
    V.Zwetkoff, Acta Physicochim. U.R.S.S. 18, 358 (1943)Google Scholar
  9. 9.
    V.Freedericks, V.Zwetkoff, Sov.Phys. 6, 490 (1934)Google Scholar
  10. 10.
    P.Chatelain, Acta Cryst. 1, 315 (1948)CrossRefGoogle Scholar
  11. 11. Gennes, Compt.Rendu 266 B 15 (1968)Google Scholar
  12. 12.
    J.L.Eriksen, Arch.Ratl.Mech.Anal. 4, 231 (1960)CrossRefGoogle Scholar
  13. 13.
    Groupe d’étude des cristaux liquides, J.Chem.Phys. (to be published)Google Scholar
  14. 14.
    R.B.Meyer, Phys.Rev.Let. 22, 918 (1969). However, in the geometrical conditions used for the determination of the 4 viscosity coefficients given in this paper, a recent computation has shown that the damping of the modes is not sensitive to piezoelectric effects (0.Parodi, to be published)Google Scholar
  15. 15.
    Orsay Liquid Crystal Group, Phys.Rev.Let. 22, 1361 (1969)CrossRefGoogle Scholar
  16. 16.
    V.Zwetkoff, Acta Physicochim. URSS, 6, 865 (1937), corrected, for the magnetic anisotropy values, following ref. 9Google Scholar
  17. 17.
    O.Parodi, to be publishedGoogle Scholar
  18. 18.
    M.Miesowicz, Nature, 158, 27 (1946)CrossRefGoogle Scholar
  19. 19.
    F.Grandjean, Compt.Rend. 172, 71 (1921)Google Scholar
  20. 20.
    Orsay Liquid Crystal Group, Phys.Let. 28 A, 687 (1969)Google Scholar
  21. 21.
    Groupe Expérimental d’Etudes des Cristaux Liquides, Col.Soc.Franç.Phys. Montpellier (1969), to be published in J.PhysiqueGoogle Scholar
  22. 22.
    M.Kleman, J.Friedel, Col.Soc.Franç.Phys. Montpellier (1969), to be published in J.PhysiqueGoogle Scholar
  23. 23.
    H.Zocher, Phys.Z. 28, 790 (1927)Google Scholar
  24. 24.
    C.W.Oseen, Trans.Faraday Soc. 29, 883 (1933)CrossRefGoogle Scholar
  25. 25.
    P.Chatelain, M.Brunet-Germain, Comptes Rendus, 266 571 (1968).Google Scholar

Copyright information

© Plenum Press, New York 1970

Authors and Affiliations

  • Orsay Liquid Crystal Group
    • 1
  1. 1.Service de Physique des SolidesFaculté des SciencesOrsayFrance

Personalised recommendations