Investigation of relaxation processes in MHPB(H)PBC antiferroelectric liquid crystal by dielectric spectroscopy

摘要

The molecular dynamics of a recently synthesized chiral antiferroelectric liquid crystal (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl-4'-(3-butanoiloxyprop-1-oxy)biphenyl-4'-carboxylate (in short MHPB(H)PBC) exhibiting SmA~* and SmC_A~* phases have been studied in the frequency range of 1 Hz to 10 MHz. In the SmA~* phase only one doubly degenerate soft mode relaxation exists which becomes critical at transition temperature and it splits into two modes in SmC_A~* phase, one at high frequency about 500 kHz, the other at low frequency about 40 kHz. Relaxation frequencies of both modes decrease slowly with decrease in temperature. These two observed modes are due to the anti-phase and in-phase azimuthal angle fluctuations of the molecules in the anti-tilt pairs. The temperature dependence of the dielectric strengths and relaxation frequencies, determined by Cole-Cole plot clearly reveals that SmA~* to SmC_A~* transition is weakly first order.