A neutron scattering study of orientational ordering in the smectic and nematic phases of the liquid crystal, 2',3'-difluoro-4-heptyl-4"-nonyl p-terphenyl

Hamley, I.W., Luckhurst, G.R., Richardson, R.M. and Santos, F. (2002) A neutron scattering study of orientational ordering in the smectic and nematic phases of the liquid crystal, 2',3'-difluoro-4-heptyl-4"-nonyl p-terphenyl. Journal of Chemical Physics, 116 (9), 3887-3899. (doi:10.1063/1.1446435).

Abstract

The orientational order parameters (P) over bar (2), (P) over bar (4), and (P) over bar (6) have been determined by neutron scattering from a mixture of normal hydrogenous and deuterium labeled molecules in the nematic, smectic A and smectic C phases of the mesogen 2',3'-difluoro-4-heptyl-4"-nonyl-p-terphenyl. Since the method relies on a knowledge of the molecular structure, the influence of different molecular conformations resulting from the terminal chains on the values determined was examined in detail. It was shown that the choice of conformation could significantly effect the resulting values of the order parameters. The order parameters were, therefore, determined by assuming a distribution of conformations for the alkyl chains. The relative contributions of these conformations were governed by the Flory rotational isomeric state model. The values for (P) over bar (2) were consistent with those determined by nuclear magnetic resonance but all the order parameters were generally much greater than those predicted by the Maier-Saupe theory.

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