Amplitude and phase fluctuation modes of a newly synthesized anti ferroelectric liquid crystal material 4F6Bi

Abstract

Frequency and temperature dependent dielectric spectroscopy of a newly synthesized anti ferroelectric liquid crystal (AFLC) material namely “(S)-(+)-(1-methylheptyloxycarbonyl)phenyl 4′-(6-perfluoropentanoyloxyhex-1-oxy) biphenyl-4-carboxylate ((S) (4F6Bi))” has been carried out in the frequency range 1 Hz to 1 MHz under planar anchoring conditions of the molecules. 4F6Bi possesses paraelectric (SmA ⁎), ferroelectrics (SmC ⁎), and wide range anti ferroelectric (SmC A ⁎) phases. The SmA ⁎ phase shows soft mode relaxation related with the tilt fluctuations. Its relaxation frequencies are highly temperature dependent and decreases with decrease in the temperature. Dielectric strength is small (~ 1.0–2.5) but increases with decrease in temperature and follows Curie–Weiss' law. The SmC ⁎ phase shows Goldstone mode with its dielectric strength slowly increasing with decreases in the temperature, and shows maximum value (~ 64) just above the SmC ⁎–SmC A ⁎ transition at 118.1 °C. Goldstone mode relaxation frequency has been found to be almost invariant with temperature (~ 3.5 kHz). Two modes of dielectric relaxation have been observed in the SmC A ⁎ phase due to anti ferroelectric ordering of molecules.