Thermodynamic, optical and dielectric properties of the twisted grain boundary phases of the homologous series of 4-n-alkyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy) chalcone

Abstract

Dielectric, thermodynamic and optical properties of the homologous series of newly synthesised optically active non-symmetrical liquid crystalline dimeric compounds 4-n-alkyloxy-4′-(cholesteryloxycarbonyl-1-butyloxy) chalcone (with tail length = 10, 11, 12) having wide temperature ranges of two twist grain boundary (TGB) phases, namely TGBA and TGBC*, have been studied using impedance spectroscopy, differential scanning calorimetry and polarised light microscopy. The dielectric studies have been carried out in the frequency range of 1 Hz–35 MHz for planar and homeotropic configurations. The experimental dielectric spectra display two feeble collective relaxation modes for the planar oriented sample. One mode, which exists in the MHz region, has behaviour similar to that of the soft mode due to amplitude fluctuations. The second mode exists in the low-frequency region (∼100 Hz) and appears due to phase fluctuations, as happens in the case of the Goldstone mode. Results support the recently proposed theory for the soft and Goldstone mode relaxations of TGB phases. Various electrical parameters have been determined for the two TGB phases of the above‐mentioned compounds.