Field-induced director dynamics in a nematic liquid crystal: a molecular site dependence?

Luckhurst, G.R., Miyamoto, T., Sugimura, A. and Timimi, B.A. (2002) Field-induced director dynamics in a nematic liquid crystal: a molecular site dependence? Journal of Chemical Physics, 116 (12), 5099-5106. (doi:10.1063/1.1452106).

Abstract

Studies of the field-induced alignment of the nematic director for low molar mass materials using vibrational spectroscopy have revealed some fascinatingly unexpected results. Several studies have found that the relaxation time for the director alignment is dependent on the group in the molecule used to monitor the director orientation. Seemingly this undermines the basic concept of the Leslie-Ericksen hydrodynamic theory of nematics. Here we report complementary studies using deuterium NMR spectroscopy of perdeuteriated 4-pentyl-4'-cyanobiphenyl where the director is aligned by a magnetic or an electric field. This particular technique was chosen because the spectral peaks associated with each rigid group in the molecule are clearly resolved and of comparable intensity. We have investigated the director alignment using different temperatures, electric field strengths and angles between the magnetic and electric fields, each of which influences the director relaxation time. For all of the experiments we find that the relaxation times are independent of the group used to determine the director orientation during the alignment process.

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