Dielectric relaxations in a liquid crystal along with thermistor application.

Abstract

A thermotropic hydrogen bond liquid crystal ClBAO + 6BAO is synthesized by mixing in equimolar ratios of chlorobenzoic acid and hexyloxybenzoic acid. FTIR studies conform the formation of hydrogen bond between the precursors. This mesogen exhibits nematic phase with long thermal range. DSC thermogram specified the transition temperatures and their respective enthalpy values. Dielectric spectroscopy is performed in the range between 5Hz and 13MHz; two types of relaxations, namely type 1 and types 2, are identified and studied extensively. Both of these relaxation are observed to follow Debye relaxation behavior. Type 1 relaxation process, referred as soft mode, is examined at 1kHz; a mild shift in the relaxation frequency is noticed as temperature decreased. Type 2 relaxation is observed at 9.4MHz, and the relaxation frequency magnitude shifted to 10.61MHz with decrement in the temperature. Cole-Cole plots are constructed for both of these relaxation, and the corresponding activation energy is experimentally deduced from the Arrhenius plots. Another interesting observation is the temperature response of this mesogen to resistance. Both positive and negative slopes are identified in thermos-resistive plots thus by modulating the liquid crystal temperature. Perhaps, this is the first report to notice both behaviors in a mono-mesogen segregated by few degrees of temperature. Features of dielectric studies and thermistor applications are discussed in detail.