Short- and long-time responses of dielectric permittivities in the shear-induced precessional region of liquid crystal 8CB

Abstract

In the nematic phase of 8CB (4-n-octyl-4′-cyanobiphenyl) under the shear flow, it has been suggested that in the temperature region of α2/α3 < 0, a flow instability occurs: the flow alignment of the director changes to a tumbling motion of the director about the neutral axis. If the transient response of the dielectric permittivity is measured in the tumbling region, damped oscillation of the director has been identified. In our present study, if the shear flow is inverted at a time t0 after the initiation of the flow, we could find that some echo of the tumbling motion can be observed in the dielectric measurements. The amplitude of the echo becomes weak when the temperature is decreased to N-SA phase transition point. These phenomena are discussed on the basis of the critical behavior of the director motion.