MEASUREMENT OF RHEOLOGICAL PROPERTIES FOR SMECTIC-A LIQUID-CRYSTAL BYUSING ULTRASONIC RHEOMETER AND ROTATIONAL VISCOMETER

The relationship between the rheological properties and the alignment direction of liquid crystals was studied using a rotational viscometer and an ultrasonic rheometer. 4-Cyano-4'-n-octylbiphenyl (8CB) was use d for the sample. The measurements of viscosity for 8CB were carried o ut using the rotational viscometer having parallel plate geometry. The parallel plates were made from glass and covered by polyimide film wi th rubbing to align the liquid crystal molecules, The oriented structu re of 8CB was examined using a polarizing microscope optical system wh ich was built in the rotational viscometer. When the direction of shea ring was perpendicular to the layers of smectic 8CB, the apparent visc osity was higher than that in the case of no-rubbing. Viscoelastic pro perties at ultrasonic frequency (3 MHz) were examined by the ultrasoni c rheometer using a fused-quartz delay line. When the shear wave vibra tion was perpendicular to the smectic layers, G' was observed, However , when the shear wave vibration was parallel to the smectic layers, G' was not observed. (C) 1997 Elsevier Science S.A.