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An EPR study of order and molecular orientation in liquid crystals MacKay, Alexander Lloyd

Abstract

Using EPR, the temperature dependence of the effective order parameter of the molecule vanadyl acetylacetonate in the nematic liquid crystal 4-methoxy benzylidene-n-butyl aniline was studied. In the resulting data, a discontinuity in slope of the curve of effective order parameter versus temperature was found, indicating a change to a more restricted type of motion at lower temperatures. Similar results were obtained from NMR T₁ measurements on the pure liquid crystal. The discontinuity cannot be interpreted solely as a viscosity effect. Two cholesteric liquid crystal mixtures containing vanadyl acetylacetonate were subjected to a high magnetic field (~20 kilogauss). Prom EPR measurements, a 1.75:1 mixture by weight of cholesteryl chloride and cholesteryl myristate was found to orient its helix axis parallel to the field direction. In a.2 percent by weight mixture of cholesteryl chloride in nematic 4-methoxy benzylidene-n-butyl aniline, the molecules tended to arrange their long axes parallel to the field thus making the helix axis perpendicular to the field.

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