Ambient Smectic Ordering in Hydrogen-Bonded Liquid Crystal Homologous Series

Abstract

A homologous series of compounds with an inter-hydrogen bond formed between p-n-alkyloxy benzoic acids (nABA) and alkyl aniline were synthesized and characterized. The mesogenic p-n-alkyloxy benzoic acids (where n represents the alkyloxy carbon number from 3 to 12 except 4 and 6) formed a hydrogen bond with liquid-crystal intermediate 4-dodecyl aniline. The isolated homologous series compounds were analyzed by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (P-NMR), and dielectric studies. The occurrence of an ambient smectic ordering in some of the isolated mesogens was one of the interesting features of these homologous series. The phase diagrams of the p-n-alkyloxy benzoic acids and the present homologous series were computed and compared and it can be mentioned that there exists a correlation between the alkyl chain length and mesogenic phases induced. Further, some of the mesogens exhibit monotropic smectic F and smectic G transitions. The hydrogen bond formation was evinced through FTIR and P-NMR spectral studies. Results of free p-n-alkyloxy benzoic acids and the hydrogen-bonded homologous series are discussed in the light of increment alkyloxy carbon number, mesogenic phases exhibited, and mesogenic thermal range.