Study and Characterization of Double Hydrogen-Bonded Liquid Crystals Comprising p-n Alkoxy Benzoic Acids with Azelaic and Dodecane Dicarboxlic Acids

Abstract

Two series of double hydrogen-bonded liquid-crystalline complexes have been designed and synthesized. Dodecane dicarboxlic acid (DDC) and azelaic dicarboxlic acid (AC) belong to the same family of dicarboxlic acids having similar structural properties but with increasing H-C-H spacer groups. A successful attempt has been made to form hydrogen bonding between DDC and AC with p-n-alkyloxy benzoic acids (nOBA) by varying the respective alkyloxy carbon number and the physical properties exhibited by the individual series. The first series comprises DDC and p-n-alkyloxy benzoic acids (nOBA) and the other series is formed between AC and nOBA, where n represents the alkyloxy carbon numbers from 5 to 12 (except 6). These two homologous series are analyzed by polarizing optical microscopy (POM), differential scanning colorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and proton nuclear magnetic resonance (NMR) studies. The formation of an inter-hydrogen bond is evinced through FTIR and 1H NMR. An interesting feature of DDC + nOBA homologues series is the stabilization of the higher order smectic C phase with increasing chain length. In the AC + nOBA homologues series a smectic G phase is induced with the increment of alkyloxy number. Phase diagrams of the above complexes are computed and compared. An even–odd effect in both series is discussed with respect to the enthalpy values at the isotropic to nematic phase.