Structural investigation of some calamitic liquid crystals and fabrication of liquid crystal based sensors for detection of hydrazine vapour and mercuric ion in water

Abstract

Liquid crystal (LC) is referred as curious state of matter and its impact on modern technology has been profound because of its unique mesogenic properties. LCs have potential applications in numerous areas, especially in the field of display, electro-optics, thermoconducting materials and fast switching devices. The characterization of the liquid crystalline behavior is usually achieved by three techniques: polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). POM is based on birefringent property of LC materials. DSC is based on fact that all the phase transitions (solid-mesophase, mesophase-mesophase and mesophase-isotropic phase) are accompanied with an enthalpy change. The XRD reveals structure of the mesophase. It is of fundamental interest to understand molecular structure and interactions responsible for formation and stability of LC phases. Raman spectroscopy having molecular origin has this potential and in addition it can determine the accurate transition temperature. Recently, LCs have proved themselves as a fresh entrant for developing innovative sensing systems. The alignment of LC molecules is extraordinarily sensitive to molecular and chemical binding. The detection through LC based sensor can be carried out in ambient light without applying electrical current or molecular labeling. Also the optical signal in LC based sensor can be visualized easily with the naked eye without any need of complex instruments. These important characteristics of LC based sensors make them well suited for simple detection high sensitivity and low-cost assays. The present thesis has been systematically organized into seven chapters. newline