Measurements of the Rotational Viscosity Coefficient and the Shear-Alignment Angle in Nematic Liquid Crystals

A method is described for the direct measurement of the shear-alignment angle in a nematic liquid crystal. Results of such measurements are reported for the nematic phases of three compounds: PAA (p, p^'-azoxydianisole), MBBA (p-methoxybenzylidene-p^'-n-butylaniline), and HBAB (p-n-hexyloxybenzylidene-p^'-aminobenzonitrile). We also report measurements of the rotational viscosity coefficient for the same compounds. In contrast to a recent report by G\"ahwiller, no orientational instability was found in HBAB.