Abstract
Abstract The orientational ordering of three ferroelectric liquid crystals has been studied by 2D carbon-13 nuclear magnetic resonance with variable angle sample spinning. These liquid crystals are esters of α-chloro acids and 4-heptoxy-4′-hydroxybiphenyl, and have very large spontaneous polarization. Since the helical structures of the optically active compounds are retained at a magnetic field of 7.05 T, their racemates were studied. The 2D NMR technique used was separated local field (SLF) spectroscopy with an efficient proton-proton dipolar decoupling sequence BLEW-48 in the evolution period. The carbon-proton dipolar coupling constants were obtained and the order parameters for different molecular segments of the liquid crystal were calculated. The C-13 chemical shifts were measured as functions of temperature and the data were used to obtain the temperature dependence of order parameters. The relations between the order parameters, molecular structures, and phase behavior are discussed.
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