The Effect of Twist on Biaxial Ordering in the Cholesteric Phase
Deuterium magnetic resonance and optics have been used to study chiral nematic materials composed of compounds selectively deuterated at specific sites. The deuterated materials are 4-methoxybenzylidene-4′-butylaniline (MBBA) selectively deuterated in the α position (MBBA-α-d2) and on one aromatic ring (MBBA-2′-3′-5′-6′-d4). To each of these materials was added 4-methoxybenzylidene-4′-[(+)-2-methyl-butyl]aniline (MBMBA) in various quantities to obtain samples of different pitch length. From deuterium spectral patterns, values were obtained for the asymmetry parameter η, from different sites of the molecule. These data show that the mechanism responsible for 2H-NMR biaxiality is anisotropic fluctuations of the molecular long axis. Measurements of η in the vicinity of the blue phase suggest that this phase may be initiated by a characteristic value of η in these materials. New 2H-NMR spectral patterns of the blue phase are shown.
KeywordsLiquid Crystal Asymmetry Parameter Nematic Phase Spectral Pattern Molecular Axis
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