Absolute Measurement of the Critical Properties of Second Sound at the Smectic- A —to—Nematic Phase Transition in 8OCB

Light scattered from the driven free surface of the smectic-A phase of octyloxy cyanobiphenyl (8OCB) provides a low-frequency measurement of second sound. This yields an absolute measurement of the smectic elastic constant, B. There is no dispersion in either the angular or frequency dependence of B for angles 35^∘{}-83^∘{} from the normal and for frequencies from 10-100 kHz. Near the smectic-A---to---nematic phase transition the smectic elastic constant can be described by B=(6.03±0.05)×10⁷ (TNA-T)^0.32±0.015 dyn/cm².