X-ray Photographic Studies of Liquid Crystals I. A Cybotactic Nematic Phase

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Abstract
The X-ray diffraction patterns of the nematic phase of bis-(4′-n-octyloxybenzal)-2-chloro-1, 4-phenylenediamine show major maxima at two diffraction angles. The ones at the larger angle are due to the interaction of neighboring, parallel molecules and the average distance between the long axes of the molecules can be calculated using the formula 2d sin θ = 1.117γ. The maxima at the smaller diffraction angle are related to the length of the molecule; the observed diffraction pattern is explained by assuming that a part of the molecules are organized in groups (cybotactic groups) in such a way that the ends of the molecules lie in fairly well defined planes making an angle of about 45° with the direction of the long axis of the molecules. At lower temperatures the large majority of the molecules are arranged in these groups, and the groups appear to be fairly rigid. At higher temperatures the groups become less prominent, but they do not completely disappear.