Chemical and optical characterization of linear hydrogen bonded thermotropic liquid crystal dimers

Design, synthesis and characterization of seven linear hydrogen bonded thermotropic liquid crystals derived from mesogenic p-n-heptyloxy benzoic acid (7BAO) and p-n-alkyl benzoic acids (nBA, where n varies from 2 to 8) are described in this work. Hydrogen bonding and chemical environment of the proposed molecular structure have been confirmed by FTIR and 1H, 13C NMR studies respectively. The isolated mesogens are characterized for the optical and thermal behaviour. The phase transition temperatures and their corresponding enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. Polarizing Optical Microscope (POM) and DSC data are further utilized for the construction of phase diagram. Odd-even effect is observed in the corresponding transition temperatures across the isotropic to nematic phase transition. The order of phase transition is examined by computing Navard and Cox ratio from the peak heights of the DSC thermograms recorded. In addition to the above characterization techniques, light filtering action in the nematic phase has also been carried out.