A light scattering study of correlations in molecular orientation of a nematic liquid crystal



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Certain substances exhibit mesophases between the solid and isotropic liquid phases. In these mesophases the substance has anisotropic properties of the solid while simultaneously- displaying fluid properties of a liquid. Such substances are called liquid crystals. The mesophases are of three types: smectic, nematic, and cholesteric, all of which appear in a variety of textures, depending on the environment and history of the substance. The fundamental difference between the mesophases is the type of ordered arrangement of the cigarshaped molecules. Optically these substances behave as positive uniaxial crystals when in the smectic or nematic mesophase. Thermal agitation causes the molecules to fluctuate about their equilibrium positions, and since the molecules are asymmetric, fluctuations of twist, bend, and splay are present. These describe fluctuations in orientation of the molecules in a volume element with respect to the local molecular orientation direction. Splay is a fan-like expansion, the spread turning away from the equilibrium orientation axis. [...]