Nonconventional hydrodynamics of smectic-A phases of liquid crystals: An experimental study of various compounds with the use of ultrasound.

Abstract

This study concerns ultrasonic velocity and damping in the smectic-A phases of four liquid crystals, using a resonance technique. The compounds studied are terephthal-bis-p-p'-butylaniline (TBBA), octylcyanobiphenyl (8CB), octyloxycyanobiphenyl (8OCB), and p-cyanobenzylidene-p-octyloxyaniline (CBOOA). The results obtained for TBBA reveal abnormal damping behavior which shows that conventional hydrodynamics does not apply in the smectic-A phases of liquid crystals. Analysis of these results shows that anharmonic effects related to fluctuations in the smectic layers have an order of magnitude which is compatible with the lowest-order predictions of the theory of Mazenko, Ramaswamy, and Toner (MRT), when \ensuremath{\delta}${\ensuremath{\eta}}_{5}$0. Measurements taken on 8CB 8OCB, and CBOOA show that anharmonic effects are negligible in these three compounds at ultrasonic frequencies. This result is consistent with the lowest-order predictions of MRT theory. The difference between the behavior of TBBA and that of the other three compounds shows that anharmonic effects only appear at ultrasonic frequencies in compounds with a sufficiently high B/${K}_{1}$ value (B and ${K}_{1}$ are the layer compressibility and splay constants, respectively).