Flow Properties of Nematic 8CB: An Example of Diverging and Vanishing α3

Abstract

The temperature dependence of the Leslie viscosities α₂ and α₃ has been measured in the nematic liquid crystal 8CB (octyl-cyano-biphenyl), using a trosional shear flow apparatus. In most nematics studied so far α₃ is found to be everywhere negative, but if the nematic has an adjacent semectic. A phase at lower temperatures, it can be expected that α₃ changes sign and becomes positive in the vicinity of T_NA as a precursory phenomenon of the transition. In fact this influence is dominating the major part of the nematic phase. We have found that for 8CB α > 0 in the whole nematic range (33.5°C-40.1°C), except for a small temperature interval of one degree just below the clearing point. This leads to intrinsic flow instabilities, but the flow can be stabilized by applied electric fields. The results further contain the first measurement of a diverging α₃ in a flow experiment.