Thermal Analysis, Calorimetric and Electrical Polarization Studies in Smectic X* Phase of Hydrogen-Bonded Ferroelectric Liquid Crystals

Abstract

Intermolecular hydrogen-bonded ferroelectric liquid crystals are isolated and characterized. Formation of hydrogen bond is evinced by Fourier Transform Infra-Red (FTIR) studies. Phases are confirmed by polarizing optical microscopic (POM) studies and further confirmed by Differential Scanning Calorimetry (DSC) thermograms. Phase diagram is constructed from POM and DSC data and the order of transition possessed by the individual phases are evaluated from the Cox parameter. Summation of the enthalpy values exhibited by the individual complexes both in heating and cooling cycles are compared to verify the thermal equilibrium exhibited by the system. Mono variant smectic X* phase observed in two complexes are confirmed to be smectic ordering from the tilt angle, helix, and spontaneous polarization measurements. Enhancement of smectic X* thermal range is noticed through the phase diagram of the binary mixtures. Unwinding of the helix is measured from helical pitch measurements. From dielectric studies, the threshold values for two field-induced phase transitions E₁ and E₂ are measured. Electric field–temperature (E–T) phase diagram is constructed from the threshold field values obtained with respect to the temperature variation. Further, molecular modeling is proposed for the observed electric field-induced phase transitions.

Keywords:

• Binary mixtures
• field-induced phase transition
• hydrogen-bonded ferroelectric liquid crystals
• smectic X* phase
• spontaneous polarization