Detection of phase transitions in liquid crystals through optical, thermal and electrical techniques

Abstract

A ferroelectric hydrogen bond liquid crystal is chosen for documentation of phase transition temperature by various techniques. In this article, the identification of phase transition from smectic C* to smectic G* through ten various techniques which includes optical, thermal, dielectric and electrical methods are discussed. Optical textures are the first evidence for the phase transition to occur. Smectic C* is manifested by broken focal conic texture while smectic G* is identified by smooth mosaic texture. An intense peak in the DSC thermogram provided the exact phase transition temperature along with enthalpy value of C* to G* phase. The variation of permittivity and dielectric loss with temperature also evinced C* to G* phase transition temperature. In addition to these, thermo-electric profiles of this sample are constructed between voltage and temperature at a fixed magnitude of current. An anomaly in thermo-electric profiles indicated detection of the phase transition temperature. Lastly thermo-resistive profiles are constructed for different values of temperature. An anomaly in the plot between resistance of the mesogen with temperature clearly indicates the first order C* to G* phase transition temperature.