High frequency effective viscosities of nematic liquid crystals with tilted orientation

Abstract

Using quartz crystal resonators, we have measured the effective viscosities of nematic liquid crystals (LCs) in the MHz domain. The LC orientation was switched via the command-surface effect. The dependence of viscosity on orientation cannot be explained by orientational modes. They are attributed to the emission of longitudinal sound, the latter effect requiring a tilt orientation of the nematic director with respect to the surface. Optical investigations confirm the existence of a finite pretilt angle. Sensor applications are discussed.