Thermal and Dielectric Investigations on Supramolecular Hydrogen Bonded Liquid Crystals

A novel series of linear supramolecular hydrogen bonded liquid crystals (SMHBLC) have been investigated. Complimentary hydrogen bonds are formed between p-n nonyloxy benzoic acid and various p-n alkyloxy benzoic acids whose carbon chain length varied from 5 to 12. The formed mesogens are characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Polarizing Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC). Phase diagram has been constructed through POM and DSC data. An interesting finding is the observation of a new smectic ordering, labeled as smectic X, which has been characterized by various thermal and electrical techniques. Optical tilt angle in smectic C and X phases have been measured. The theoretical mean field value beta deduced from the experimental tilt angle values is observed to be in good agreement with the predicted value. Dielectric studies revealed a low frequency relaxation mechanism in smectic C phase and the corresponding activation energy has been calculated from the corresponding dispersion curves. A worth mentioning observation is the optical shuttering action of the mesogens in nematic phase. Light filtering action of these mesogens in nematic phase has also been evaluated. Low pass, high pass, and band pass filtering action has been observed and discussed.