Effect of DC bias and cell thickness on the characteristic dielectric parameters of the relaxation modes of an antiferroelectric liquid crystal

The temperature and bias field dependent dielectric parameters of an antiferroelectric liquid crystal (AFLC) (S)-4-(1-methylheptyloxycarbonyl)phenyl-4′-(6-pentanoyloxyhex-1-oxy)biphenyl-4-carboxylate (4H6Bi(S)) have been investigated in the frequency range 0.1 Hz-10 MHz for homogeneously aligned sample cells of thicknesses 10 and 4 μm. This material possesses non polar paraelectric SmA⁎, polar ferroelectric SmC⁎ and anti polar antiferroelectric SmC⁎A phases. Dielectric strength and relaxation frequency of the soft mode are almost independent of the cell thickness. On the other hand, dielectric strength of Goldstone mode (observed in the SmC⁎ phase) is significantly diminished, whereas its relaxation frequency is increased with the decreasing cell thickness. The dielectric strengths of the usual antiferroelectric relaxation modes increase with DC bias whereas the relaxation frequencies are independent of both the DC bias and cell thickness. The domain mode in the SmC⁎ phase and a new relaxation mode in the SmC⁎A phase appear as a consequence of helix unwinding taking place due to application of DC bias.