Rayleigh Scattering of Light by Liquid Crystals
Liquid crystals are rather peculiar compounds constituted of long shaped organic molecules. Between the isotropic and the crystalline states they show intermediate phases called nematic, smectic-A, smectic-C. In all these “mesophases” the rod-like molecules are arranged with a long range orientational order. As early as 1937 Chatelain1 observed a remarkable scattering of light by the nematic phase: the scattered intensity was typically 104 times larger than in the isotropic phase and the light was strongly depolarized. To explain this observation the old concept of “swarms” was used. This concept was abandoned only thirty years later with the interpretation of de Gennes2: the scattering properties of nematics are in fact due to orientational fluctuations of the molecules. These fluctuations, excited by thermal energy, are controlled by the elastic properties of the nematic. In other “mesophases” a different elasticity gives rise to other kind of orientational fluctuations: thus can be understood a reduced scattering for smectics-A and an intense scattering again for smectics-C. Here I will first present briefly the most common phases of liquid crystals and their elastic properties. The readers interested in a more detailed description should refer to reference 3. I will then distinguish the various types of orientational fluctuations responsible for light scattering. The change from one type to the other can be continuous near second order or weakly first order phase transitions: thus the more fundamental problem of phase transitions can be tackled in the last section.
KeywordsLiquid Crystal Photon Correlation Spectroscopy RAYLEIGH Scattering Nematic Phase Isotropic Phase
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- 1.P. Chatelain, Bull. Soc Franç Min 50, 280, 1937.Google Scholar
- 2.P.G. de Gennes, C.R. Acad. Sci., 266 B, 15, 1968.Google Scholar
- 3.P.G. de Gennes, “The Physics of Liquid Crystals”, Oxford Press 1973.Google Scholar
- 4.Groupe d’Etudes des Cristaux Liquides (Orsay), J. Chem. Phys. 51, 876, 1969.Google Scholar
- 6.Orsay Liquid Crystal Group in Liquid Crystals and Ordered fluids, Plenum Press, New York.Google Scholar
- J.D. Litster, Capri School, 1974.Google Scholar
- 10.Y. Galerne, J.L. Martinand, G. Durand, M. Veyssié, Phys. Rev. Lett., 29, 561, 1971.Google Scholar
- 11.C.Y. Young, N.A. Clark, Proceeding of Kent Conference on Liquid Crystals, 1976.Google Scholar
- 13.D. Salin, I.W. Smith, G. Durand, J. Physique, 35, 165,1971.Google Scholar
- 14.M. Delaye, P. Keller, Proceedings of Kent Conference, 1976 and to be published.Google Scholar
- 18.M. Delaye, J. de Physique, C3, 99, 1976.Google Scholar
- 19.H. Birecki, J.D. Litster, Proceeding of the Kent Conference, 1976.Google Scholar