Abstract
The constituent molecules of liquid crystals usually contain an aromatic core and one or more flexible alkyl chains. NMR studies of order parameter profiles in these molecules have revealed [4.1] that the ordering of their rigid segments varies with respect to each other and with temperature. Due to internal degrees of freedom, the chain therefore does not always exist in an all-trans conformation. Specifically, the ratios of deuterium quadrupolar splittings Δv i are temperature-dependent. Attempts were made to interpret these ratios using an ordering matrix for all conformers of the molecule [4.2]. This is only possible if it is assumed that molecular conformation is independent of molecular orientation, thereby separating the internal and overall motions [4.3] of the molecule. This also implies that the internal energy of a conformer is independent of the orientation [4.4]. The temperature dependence of ratios of Δv i was then attributed solely to the variation in S xx — S yy with temperature [4.2]. Others explained this either by the distribution [4.5] or the geometry [4.6] of different conformational states. Prom these studies the conclusion is stated that one single order matrix is insufficient to describe molecules with many conformational states.
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© 1994 Springer-Verlag New York, Inc.
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Dong, R.Y. (1994). Molecular Field Theories of Flexible Nematogens. In: Nuclear Magnetic Resonance of Liquid Crystals. Partially Ordered Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4684-0208-7_4
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DOI: https://doi.org/10.1007/978-1-4684-0208-7_4
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