Study of the Orientational Order in Liquid Crystals by X-Ray Scattering

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Abstract
This review presents the analysis of the possibilities of the X-ray scattering method to study the orientational order and short-range correlations in liquid crystals. The general theory of X-ray scattering in nematic liquid crystals is presented and various approximations and assumptions made in the literature, are critically analysed. A simple model of the nematic phase is introduced which allows for the direct calculation of the scattering intensity. The comparison between the model results and the existing experimental data enable one to single out the most important molecular parameters, which determine the distribution of the intensity in reciprocal space and to justify the method for the measurement of the nematic order parameter. The investigation of different types of intermolecular correlations in liquid crystals with the help of low-angle scattering is also discussed. Finally, there is a section on the influence of smectic fluctuations on the X-ray scattering data, with the emphasis on the nematic phase with two competing fluctuating density waves of different wave vectors.