Experimental Observation of Induced Thermochromic Effect and Nematic Defects in Hydrogen Bonded Liquid Crystals

T. Vasanthia, V Balasubramanianb, S. Radjarejesrib, V.N. Vijayakumara aDepartment of Physics, Condensed Matter Research Laboratory (CMRL), Bannari Amman Institute of Technology, Sathyamangalam 638 401, India bDepartment of Science, Sona College of Technology, Salem 636 005, Tamil Nadu, India

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Hydrogen bonded liquid crystal mixtures are derived from: (i) non-mesogenic compounds of diglycolic acid (DGA), (ii) mesogenic compounds of 4-amyloxybenzoic acid (5OBA) and (iii) 4-hexyloxy benzoic acid (6OBA). The existence of intermolecular H-bond is confirmed with FTIR and validated using the density functional theory studies. Polarized light microscopy and differential scanning calorimetry are used to observe the phase variations and transition temperature. In addition, enthalpy values of different mesogenic phases are determined. It is worth mentioning that the nematic mesogenic defects with S=±1 and S=+1/2 are also analyzed. In order to discuss the induced higher order smectic F phase and its stability, the density functional theory study is applied. The band gap energy of the hydrogen bonded liquid crystal mixtures is found to be 5.1780 eV, based on the HUMO-LUMO approach. This induced thermochromic effect of hydrogen bonded liquid crystal mixtures is a useful phenomenon that can be utilized in optical device applications. In this paper, variation on liquid crystal parameters as well as the formation of H-bond between an acceptor and a donor, along with the extension of a chain length, are also reported.

DOI:10.12693/APhysPolA.139.139 topics: nematic defect, smectic F, thermochromic effect, POM