Rotational viscosity in the smectic phases of terephthal-bis-butylaniline (TBBA)

Abstract

Measurements of rotational viscosity in the various liquid crystalline phases of TBBA (terephthal-bisbutylaniline) are reported. The quantity measured is the viscous energy dissipation in the liquid crystal as it oscillates in a magnetic field. This dissipation varies greatly in the different smectic phases. It is small in the $A$ and $B$ phases, but large and strongly temperature dependent in the $C$ phase. This behavior is explained in terms of the structure of these phases. The smectic $A$ to smectic $C$ transition is of second order, and the dissipation increases dramatically at the transition point. The critical behavior is found to fit mean-field theory, rather than a predicted heliumlike behavior.