Design synthesis and characterization of blue phase induced hydrogen bonded nanoliquid crystalline complexes for optical device applications

Abstract

A novel blue phase hydrogen bonded ferroelectric liquid crystal (HBFLC) series has been synthesized from cholesteryl stearate (CHS) and p-n-alkyloxybenzoic acid (nOBA, where n = 2 to 12). Blue phase (BP) liquid crystalline complex is a high potent material for next generation optoelectronic devices. The structural, optical and thermal properties of present HBFLC complex have been characterized by various techniques such as, X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Nuclear magnetic resonance spectroscopy (NMR), Polarizing Optical Microscope (POM) and Differential Scanning Calorimetry (DSC) techniques. Band gap energy of the present HBFLC complex (4.6eV) is estimated by UV-Visible spectrometer. X-ray diffraction reveals the monoclinic nature of the HBFLC complex whereas Scanning Electron Microscopic (SEM) studies disclose the morphology of the present complex. Phase diagram of the CHS+nOBA HBFLC complex is constructed from DSC data and phase behavior is discussed. The lower homologous of CHS+nOBA HBFLC (n = 2 to 6) complex shows BPsm1, BPsm2, BPsm3 while higher homologous (n = 7 to 12) exhibiting orthogonal smectic A* (Sm A*) character with blue phases. A noteworthy observation is that the identification of extended thermal span of the smectic blue phase and induced Sm A* phase in the present HBFLCs. Another important observation is that the BP wider range is reported in the present Hydrogen Bonded Ferroelectric Nanoliquid Crystalline (HBFNLC) complex which is more suitable for photonic devices. In addition, LC parameters such as, phase width, thermal stability factor, phase transition temperature with enthalpy value and the origination of orthogonal phases in CHS+nOBA HBFLC complex have been reported. Another Liquid Crystalline (LC) mixture is prepared from the chiral compound of Cholesteryl Nonanoate (CN) and non-chiral compound of biphenylpyrimidine (BPP). The phase change with temperature and its corresponding texture of the binary mixtures are analyzed by Polarizing OpticalMicr