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ABSTRACT
Present supramolecular hydrogen bonded liquid crystal (HBLC) complex is obtained between mesogenic 4-nonyloxybenzoic acid (9OBA) and non-mesogenic citric acid (CA). A phase transition temperature and enthalpy values are calculated by differential scanning calorimetry (DSC) and phase behaviour are identified by polarizing optical microscope (POM). The liquid crystal parameters and structure are characterized by POM, DSC, FT-IR, NMR and optical tilt angle studies. The DSC and POM reveals the smectic and nematic phase transitions in the present complex. The molecular structure of HBLC complex is elucidated by Proton Nuclear Magnetic Resonance (1H NMR). The noteworthy in the present complex is the nematic and Smectic C phase is separated by a Smectic X phase which shows the finger print textures. The Smectic X phase is estimated by varying the mole ratio of the CA+9OBA from 1:1 to 1:3. Molecular tilt with respect to the director the Smectic X and Smectic C phase data are fitted to a power law equation in the optical tilt angle studies and it follows the Mean Field Theory. The 1:2 mole ratio of CA+9OBA shows monotropic Smectic C phase. Another creditable observation is that while the mole ratio of 9OBA mesogenic compound increases the nematic range also increases in the present HBLC complex.
Acknowledgments
The authors (V N Vijayakumar) acknowledge the financial support rendered by Department of Science and Technology (No. SERB/F/7454/2013–2014 dated 21.02.2014), New Delhi and Department of Atomic Energy (No: 34/14/14/2016-BRNS/34039 dated 22/04/2016) – Board of Research in Nuclear Science (DAE-BRNS) and infrastructural support provided by Bannari Amman Institute of Technology.