Optical Shuttering and Filtering Action in Nematogens of Supra Molecular Hydrogen-Bonded Liquid Crystals

Abstract

A novel series of linear supra molecular hydrogen-bonded liquid crystals (SMHBLC) have been isolated. Complimentary hydrogen bonds are formed between various alkyloxy benzoic acids. The formation of hydrogen bond is conformed by FTIR studies. This series exhibits rich phase variance as evinced by various textures through polarizing optical microscopic (POM) studies. Differential scanning calorimetry (DSC) studies revealed that the transition temperatures and corresponding enthalpy values are elucidated from the DSC thermograms. 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. This phase has been characterized by various techniques. Optical tilt angle in smectic C phase of various homologues has been measured and fitted to theoretical values. The critical exponent β value estimated by fitting the data of tilt angle is found to agree with the Mean Field prediction. Light filtering action of these mesogens in nematic phase has been studied. It is interesting to find that the magnitude of the cut off frequencies in higher homologues is almost similar while lower homologues behave as a band pass filter. Another unique feature is the observation of a notch filtering action in one of the homologue. Yet another interesting finding is the optical shuttering action of the mesogens in nematic phase. On application of an external field at a threshold field, these mesogens inhibits light thus behaving as optical shutters. In view of the above properties, these mesogens can be exploited for commercial applications.