Asymmetry in molecular ordering in the nematic phase: DMR study

Abstract

Deuterium nuclear magnetic resonance (2H-NMR) was performed on the rigid perdeuterated fluorene segment of the compound 2-fluorenyl-4′-tetradecyloxy benzoate (FLOC 14-d9) to unambiguously measure the order parameter U which reflects the degree of asymmetric ordering of the molecule in the nematic liquid crystalline phase. Measurements of U showed this parameter to be finite at all temperatures in the nematic phase indicative of the uniaxial phase U2 described in the Allender–Lee generalized Landau theory. Mixtures of FLOC 14-d9 with compounds consisting of molecules more cylindrical in shape were also studied to examine their effect on the parameter U. Other parameters such as the degree of order S and the orientation of the principal axes of the Maier–Saupe order matrix were measured and are discussed.