Orientational ordering of rod- and disk-like mesogens with flexible alkyl chains

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Abstract
A model has been developed by Emsley, Luckhurst, and Stockley to calculate the potential of mean torque for flexible molecules and to account for the observed variations in the segmental order profiles of the chain deuterons in the rod-like liquid crystals 4-n-alkyl-4′-cyanobiphenyl by deuterium NMR spectroscopy. In this paper we have applied this model to two other homologous series, one with a rod-like core (p-alkyloxybenzylidene-p-alkylaniline) and one with a disk-like core (hexaalkyloxytriphenylene), by considering the fragment which contains the deuterated alkyloxy chain. The subtle variations in the segmental order profiles are due to the geometry of the bond that governs the orientation of the chain and the symmetry of the core. The latter point is examined by using discotogens. The model involves segmental interaction parameters Xa and Xcc, and the excess energy of gauche over a trans state Etg. These values are obtained by fitting the theory to the experimental quadrupolar and/or dipolar splittings in mesophases of liquid crystals.

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