Synthesis and characterization of hydrogen bonded liquid crystal complexes by 4-octyloxy benzoic acid and some dicarboxylic acids

Abstract

Hydrogen bonded liquid crystal complexes synthesized from mesogenic 4-octyloxy benzoic acid (8OBA) and some non-mesogenic dicarboxylic acids {HOOC(CH2)nCOOH, n = 4, 7 and 8}; referred as ADA/8OBA (n = 4, Adipic acid), AZA/8OBA (n = 7, Azelaic acid) and SEA/8OBA (n = 8, Sebacic acid) are reported. Thermal and microstructural properties of the binary liquid crystal systems are investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The hydrogen bond formed between the 8OBA and dicarboxylic acid is confirmed by Fourier Transformed Infrared spectroscopy (FTIR) assay. The DSC and POM results infer that the binary complexes exhibit mesogenic smectic and nematic phases. All binary liquid crystal complexes exhibited four phase transition peaks to indicate Cr ↔ SmG ↔ SmC ↔ N ↔ I phase sequence during heating and cooling DSC scans. Similar phase sequence is also observed by POM. Effect of the heating rate on the phase transition temperatures and enthalpy changes is investigated. As the heating rate increased, the phase transition temperature and peak heights are increased, but enthalpy value generally decreased. Thermal stability factor and entropy changes are calculated. The phases and transitions are found to follow regular thermal order.