Rotational Viscosity of a Smectic-CLiquid-Crystalline Phase

Abstract

We report measurements of the rotational viscosity coefficient in the smectic-$C$ and nematic phases of heptyloxyazoxybenzene. The measurements are interpreted in terms of a model of the smectic-$C$ phase in which the molecules reorient about the normal to the smectic layers. Extrapolated to the nematic-smectic transition temperatures, the viscosity in the smectic-$C$ phase is lower by a factor of 0.4 than that in the nematic phase. A reverse pretransition effect is observed in the nematic phase.