Self-assembled liquid crystalline materials with fatty acids: FTIR, POM and thermal studies

Two new series of liquid crystalline materials with non-mesomorphic fatty acids, viz. nonanoic (C₉), capric (C₁₀), undecanoic (C₁₁), tridecanoic (C₁₃), myristic (C₁₄), palmitic (C₁₆) and stearic acids (C₁₈), are prepared with non-mesomorphic proton acceptors, viz. (4-pyridyl)-benzylidene-p-n-alkylanilines (PyBnA; n = 12 and 16). The smectic phase structures formed between the proton donor (fatty acid) and proton acceptor moieties are found due to the intermolecular hydrogen bonding (HB) and are monotropic. The presence of HB is confirmed by Fourier transform infrared spectroscopy in all the compounds. The characteristic optical textures of smectic phases are observed through polarizing optical microscope, provided with a hot stage and a camera. The phase transition temperatures and the enthalpy changes across the phase transitions are determined by differential scanning calorimetry. The smectic phase exhibited by the HB complexes is confirmed by miscibility studies as smectic-B. The stacking interactions in layers are found to influence the mesomorphism in these HB complexes.