Ultrasonic Determination of Anisotropic Shear and Bulk Viscosities in Nematic Liquid Crystals

Ultrasonic absorption measurements made in the nematic liquid crystals $p$-azoxyanisole and $p$-azoxyphenetole, which were oriented by an external magnetic field, are used to calculate anisotropic viscosity coefficients. Values of $\frac{\alpha }{f^2}$ and the anisotropy of $\frac{\alpha }{f^2}$ are found to be frequency independent for frequencies of 5-18 MHz in $p$-azoxyanisole and 3-15 MHz in $p$-azoxyphenetole. The relative angular orientation dependence of the two materials is similar.