Observation of Second Sound Using Light Scattering from a Free Surface Smectic A

A new technique for studying the second sound mode in smectic liquid crystals has been developed. Preliminary measurements for the smectic A phase of 4-n-octyloxy-4'-cyanobiphenyl (80CB) are described. We have developed a technique to prepare well aligned samples with one free surface. This free surface was electrically driven, and the resulting surface displacement was studied using an optical heterodyne technique. The elastic constant, B, and the effective viscosity, ν_eff, were determined from the spectrum of the scattered light.