Shear wave attenuation in smectic-A liquid crystals

Abstract

We have studied the shear impedance of two smectics-A when the propagation of the shear wave is along the normal to the layers. We observed that the real part and the imaginary part of the shear impedance differ significantly, indicating a relaxation process. We analysed our results on the basis of a coupling between the director fluctuations and the shear flow

Ultrasonic study of the shear mechanical impedance of butyloxybenzylidene octylaniline near the crystalline-B-smectic-A phase transition

“…The low value of the dynamic viscosity (1]' ~ 6 cp at 15 and 25 MHz) suggests that the data in the Sm-A phase are in the c~i > 1 regime. The presence of dispersion in the Sm-A phase is not specific to 40.8 and has already been observed in Sm-A phase of other liquid crystals that do not have an A-B transition [15]. Two processes may contribute to the dispersion in the Sm-A and B phases : relaxation of dislocations which do not have enough time to migrate during the period when the film is sheared, and director fluctuations which are coupled to the shear flow.…”