A 2H NMR study of orientational order, phase transitions and dynamics in a liquid crystalline compound

Abstract 2H-NMR spectroscopy is employed to investigate the orientational order in the nematic and smectic A, B, and crystal G phases formed by 4-(2-methylbutyl)phenyl 4′n-heptylbiphenyl-4-carboxylate-d18. Evidence of the lock in the trans-conformation of the first two methylene groups of the n-heptyl chain is found in the Sb and G phases. The dynamics of the aromatic molecular core are studied in a temperature interval including the SA-SB transition, by the analysis of the deuterium Zeeman and Quadrupolar relaxation times using the rotational diffusion model. Hence the diffusion constants related to the molecular spinning and tumbling motions are evaluated.

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