Author(s): Huidan Lu, Jianxiu Wang, Xiangzhi Song
A series of new hydrogen-bonded liquid-crystal complexes formed between para-substitued alkoxybenzoic acids (OBAm, where m denotes the number of the carbon in the alkoxy group, m = 4, 5, 6, 7, 8, 10) and 4′-pyridylazophenyl-4-alkoxybenzoate (PEAPn, where n represents the number of the carbon in the alkoxy group, n = 5, 6, 7 8, 10, 12, 14, 16) have been investigated by Fourier transform infrared (FTIR) Spectroscopy, differential scanning calorimetry (DSC), Polarizing optical microscopy (POM), and variable-temperature X-ray diffraction analysis. All PEAPn themselves are smectic mesogens and the hydrogen-bonded complexes show entiotropic smectic phases. The hydrogen bonding can raise the clear points of the complexes and, at the same time, decrease the melting points. The complexes were found to possess a much wider mesophase range than their corresponding individual components. The influence of the terminal chain lengths of OBAm and PEAPn on the phase transition temperatures is discussed. The results indicate that mostly the mesogenic behavior of the hydrogen-bonded assemblies exhibits a slight odd–even effect.