2A15 Off-Magic-Angle Spinningによるコレステリック液晶の高分解能NMR

概要

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High resolution NMR spectra of cholesteric liquid crystals are obtained by Off-Magic-Angle Spinning (OMAS). Using the average potential theory[1], it is shown that the pitch axes of a cholesteric liquid crystal with a positive (negative) magnetic susceptibility anisotropy are aligned along the spinning axis if the angle between spinning axis and the static magnetic field is larger (smaller) than the magic angle and that the helical structure is retained without any distortion due to the static magnetic field. A theoretical analysis shows that the ^<13>C OMAS NMR spectrum of a aligned cholesteric liquid crystal consists of sharp lines and that chemical anisotropies or order parameters can be determined from the difference between each ^<13>C shift of OMAS NMR spectrum and that of MAS. The resolution of OMAS NMR spectra is expected to be improved by spinning at a frequency much higher than a rotational diffusion coefficient. These theoretical results are verified by ^<13>C OMAS NMR experiments on a cholesteric mixtures of p-methoxybenzylidene-p-n-butylaniline (MBBA) and Cholesteryl Chloride (CC).
1998-10-12