Nuclear magnetic resonance spectroscopy in cholesteric liquid crystals. I. Orientational order parameter measurements

Abstract

NMR spectroscopy is utilized to measure the ’’nematic’’ orientational order parameter ? in a pure cholesteric liquid crystal for the first time. The character of the ¹⁹F NMR spectra in our sample of cholesteryl m‐fluorobenzoate, and its o‐isomer, is determined by anisotropic chemical shifts, dipolar splittings, random domain alignment, and fast self‐diffusion. The temperature dependence of ? and its value of 0.32 near the transition to the isotropic phase in both compounds closely resemble the behavior of nematic liquid crystals. This may suggest that similar ordering mechanisms are at work in both steryl and nonsteryl liquid crystals.