Collective and antiferroelectric dielectric modes in a highly tilted three‐ring ester

Abstract

Broadband dielectric spectroscopy was applied to investigate a newly synthesized antiferroelectric liquid crystal, (S)‐(+)‐4′‐(1‐methylheptyloxycarbonyl)biphenyl‐4‐yl 4‐(6‐heptanoyloxyhex‐1‐oxy)benzoate. Near the SmA–SmC* phase transition the soft and the Goldstone modes are observed. The temperature dependence of the soft mode dielectric strength follows the Cure–Weiss law. In a narrow range of temperature the collective and antiferroelectric relaxation modes coexist as a result of the competition between ferroelectric and antiferroelectric order in the successive smectic layers. In the antiferroelectric phase the low frequency, P_L, and high frequency, P_H, modes appear, which can be related to the in‐phase and anti‐phase azimuthal angle fluctuations of the director, respectively. The relaxation frequency of the P_H and P_L modes decreases linearly with decreasing temperature and satisfies the Arrhenius law. Some parameters involved in the extended Landau model of the SmA–SmC* phase transition could be obtained.

Acknowledgements

This work has been supported by the Fund for Scientific Research Flanders, Belgium (FWO, project G.0246.02). S.A.R. acknowledges the receipt of a senior postdoctoral fellowship from the Research Council of K.U.Leuven.