Mesogenic properties of PAA/6BA binary liquid crystal complexes

Abstract

A novel supramolecular liquid crystal complex has been designed and formed from pure liquid crystals para-azoxyanisole (PAA) and 4-hexylbenzoic acid (6BA). Thermal and microstructural properties of formed PAA/6BA binary liquid crystal complex system are investigated by differential scanning calorimeter (DSC), polarized optical microscopy (POM) and X-ray diffractometer (XRD). Fourier transformed infrared spectroscopy (FTIR) is used to confirm the formation of hydrogen bond between the PAA and 6BA molecules. The XRD results show that the molecular ordering of the hydrogen bonded PAA/6BA complex is arranged in the orthorhombic structure. The DSC and POM results clearly indicate that the PAA/6BA binary complex exhibits liquid crystalline properties due to the hydrogen bonds formed between the PAA and 6BA molecules. The PAA/6BA complex shows the phase transition peaks indicating Cr→N→I and I→N→SmA→Cr phase sequence during continuous heating and cooling, respectively, by DSC. These phase sequences have also been confirmed by POM observations. Furthermore, the effect of the heating rate on the phase transition temperature values is investigated. As the heating rate increases, the phase transition temperature values increase as well. Moreover, the activation energies for the phase transitions of the PAA/6BA liquid crystal complex are calculated by using Kissinger, Ozawa and Takhor methods. The calculated results clearly show that the phase transitions are regular.