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Abstract Some recent applications of the Oseen-Zocher-Frank elastic theory of nematic and cholesteric liquid crystals are reviewed. (1) The effects of a static magnetic field H are calculated in detail. In particular, for a cholesteric system, the spiral structure is distorted by the field and the period increases with H, up to a critical field Hc at which a nematic phase is expected. Hc is inversely proportional to the pitch of the unperturbed helix, and should be observable in systems with long periods. A cholesteric → nematic transition of this type has in fact been qualitatively observed. (2) The optical striations which are observed when a cholesteric liquid is inserted in a region of variable thickness have been shown by Cano to correspond to discontinuities of the torsion. The transition region between regions of different pitch has been analyzed in terms of a “disclination line” normal to the helical axis. (3) In a nematic liquid crystal the long wavelength thermal fluctuations of orientation can be analyzed from macroscopic elastic considerations: these large fluctuations are responsible for the strong scattering and depolarization of light measured by Chacarontelain. The angular dependence of the scattering intensity can thus be explained without any assumption on “swarms”.
P. G. de Gennes (1969) studied this question.