Synthesis, Characterization, Spontaneous Polarization and Dielectric Relaxation Studies in the Antiferroelectric and Ferroelectric Phases of an Achiral Banana Liquid Crystal: Bent-16

Author： Chalapathi P.

Publisher： Taylor & Francis Ltd

ISSN： 0015-0193

Source： Ferroelectrics, Vol.322, Iss.1, 2005-01, pp. : 53-67

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Abstract

Synthesis and textural characterization along with spectroscopic (IR) confirmation (of supra molecular bond formation) are reported for an achiral Banana Liquid Crystal (BLC) Bent-16, viz., 1,3-phynylene bis(4-hexadecylbenzoate). Bent-16 exhibits a B 2 phase which undergoes a paramorphotic change to B 2 (FE) phase with decreasing temperature. The intra-B 2 i.e., AF to FE transition is confirmed through double peaked spontaneous polarization profiles. Results of calorimetry (T c and ▵H from DSC) agree with polarization thermal microscopy (TM) and confirm first order nature of Isotropic to B 2 phase transition. Low-frequency (5 Hz–12 MHz) dielectric measurements of capacitance C (T) and capacitance dC/dT agree with TM and DSC. Two orientational relaxations viz., a low-frequency (LF ∼ 1 KHz) and a high frequency (HF ∼ 1 MHz) corresponding to a slow and fast time regimes respectively are reported. Arrhenius shift of relaxation frequency f R in LF and HF regions infer comparable activation energy in Antiferroelectric phases with the estimated energies from other experiments in other BLCs. The temperatures trend of dielectric increment ▵ ε and α-parameter estimated from off-centred Debye's dispersion in both the B 2 phases (LF and HF mechanism) support relative confinement of the dipole.