Ultrasonic impedometric studies in a smectic B liquid crystal (BBOA)

Abstract

The behaviour of a smectic B phase (BBOA) has been investigated by means of shear wave reflectance techniques in the case of propagation parallel to the normal of the layers. No transmission of the shear wave has been observed. In addition, the experimental results in the A and B phases show a relaxational process, which leads to an apparent finite value for the shear modulus. Our results are discussed in the frame-work of the de Gennes-Sarma model and appear to support this model

Shear wave attenuation in smectic-A liquid crystals

“…The observation of an apparent rigidity coefficient in smectic-A phases suggests, following the idea of a coupling between the shear flow and the director fluctuations, that the smectic-B phases which correspond to the second model (C44 = 0) would present in fact an apparent rigidity coefficient G' = c44 ~ 0 at ultrasonic and at higher frequencies. This is supported by our earlier study of the smectic-B phase of N-pbutyloxybenzylidene-p-n-octylaniline (BBOA) [19] where we have observed an apparent rigidity coefficient G' = C44 whereas it was expected that we would observe the behaviour predicted by the second model (C44 = 0) since the interlayer correlation is weak ( 2 layers) [20] compared to the ultrasonic penetration depth.…”