ANISOTROPIC ULTRASOUND PROPAGATION IN A SMECTIC-C LIQUID CRYSTAL.

The results of longitudinal ultrasound propagation in a magnetically aligned smectic-C liquid crystal (p-p prime Heptyloxyazoxy benzene) are reported. In the smectic-C phase the plane normals can lie anywhere on a cone with the axis along the magnetic field direction in which the sample was cooled. The effects of the layer normal direction and the molecular orientation within the planes on the velocity anisotropy were separated by cooling the sample into the smectic-C phase at particular orientations of the magnetic field and subsequently rotating the magnetic field. The results were analyzed on the basis of a multidomain model where the azimuthal angle of the plane normal around the field direction was averaged over.