Hydrodynamic and Nonhydrodynamic Behavior of Layer-Compression ModulusBat the Nematic–Smectic-APhase Transition in 8OCB

We present dynamic compression experiments which show that layer-compression modulus $B$ does not exhibit dispersion in the 100 Hz–1 kHz domain and varies with temperature according to a simple power law over four decades. These results indicate that the saturation effect predicted by Nelson and Toner does not exist for this compound, and that the thermal variation of $B$ determined at higher frequencies by a second-sound technique is not hydrodynamic, contrary to what is claimed. We show that it is affected by two relaxation mechanisms.