Thermal and mesomorphic properties of 8OBA/nABA(n = 3, 4) hydrogen-bonded liquid crystalline complexes

In this paper, a novel hydrogen-bonded liquid crystalline binary complex system was synthesized from pure mesogenic 4-(octyloxy)benzoic acid (8OBA) and non-mesogenic n-aminobenzoic acid (nABA, n = 3, 4) chemicals. Differential scanning calorimeter (DSC) experiments were performed to investigate the thermal properties of the synthesized samples, and polarized optical microscopy (POM) experiments were performed to investigate the mesogenic phase textures. The DSC and POM results showed that the phase sequence was Cr ↔ SmA ↔ SmC ↔ N ↔ I during continuous heating and cooling cycle. In addition, the thermal stability factor, phase transition entropy, and phase transition activation energy were calculated using DSC data. According to the calculated values, it was concluded that the mesogenic phases of the synthesized complexes occur regularly and the most stable phase is the SmC phase. Moreover, the optical tilt angle value for the SmC phase was measured and it was seen that the value increased up to 29° and 30° for 8OBA/4ABA and 8OBA/3ABA complexes, respectively. The formation of hydrogen bonds between the mesogenic and non-mesogenic molecules in the synthesized mesogenic structure was confirmed by Fourier-transformed infrared spectroscopy (FTIR). Furthermore, XRD results showed that the molecular ordering of the synthesized hydrogen-bonded 8OBA/4ABA and 8OBA/3ABA binary complexes occur in a monoclinic structure in the solid phase.