Synthesis and Characterization of Bent Liquid Crystal Phases by Microscopy, Calorimetry, Spontaneous Polarization and Low-Frequency Dielectric Relaxation Studies in Bent-7

Abstract

Synthesis of the bent-shaped (or Λ-shaped) achiral liquid crystal Bent 7, viz., 1,3-phenylene bis(4-heptyloxy benzoate) with resorcinol as central moiety is reported. Supra molecular formation is confirmed by KBr solid state IR spectra. Polarized Thermal Microscopy(TM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization(PS) experiments infer a bivariant monotropic (cooling), phase sequence viz., Isotropic → B 2 (FE) → B 5 (AF) → solid. Phase transition temperatures determined from temperature variation of Dielectric Constant (or relative permittivity ϵ r (T)) agree with TM and DSC. Dielectric dispersion reveals different re−orientation processes viz., a slow (LF∼ 1 kHZ) and a fast (HF∼ 1 MHz) one in both the B 2 and B 5 phases. Both the relaxations in B5(AF) phase follow Arrhenius shift to infer 1.12 and 0.89 eV of activation energies, respectively. Off-centred dispersion studied through the Cole-Cole plots in B 5 (AF) phase infer the increasing trend of dielectric increment Δ ϵ and distribution parameterα with decreasing temperature. Trends of Δ ϵ and α-parameter suggest a greater fall of response width during slow reorientation and a relative freezing rate during fast reorientation.