Pretransitional anomalies in the shear flow near a second-order nematic-smectic- a phase change.

Pretransitional anomalies in a shear flow near a second order nematic-smectic- A ( NA ) phase transition temperature T(NA), for liquid crystals (LC's), taking into account the fluctuations of the local smectic order parameter above the T(NA), are investigated. It is shown that the tumbling instability of the Couette shear flow for polar LC compounds, such as 4-n-octyl- 4(') -cyanobiphenyl (8CB), in the vicinity of T(NA), e.g., at a few tens of mK from T(NA) in the nematic phase, occurs at any shear rate gamma;.