Phase transition and structural studies of symmetric liquid crystal dimers

Abstract

Liquid Crystal is a thermally stable intermediate phase that appears between solid and liquid phases of compound. There may be several intermediate phases which are also known as mesophases in case of a particular compound. These intermediate phases posses anisotropy properties of the solid and flow property of the liquid. The basic requirement of the occurrence of liquid crystals is that there should be some anisotropy in the geometrical shape of the molecules (rod like or disc like). First discovered by an Austrian botanist, Friedrich Reinitzer in 1888, in a cholestric compound, the progress in the research and application of liquid crystals is steady and rapid in the initial period, slow in the mid period but explosive and fantastic in the last decade. The research field of liquid crystals has developed into a major field of research involving Physicists, Chemists, Mathematicians and technologists. Now a days, the liquid crystals have vast potential in the technological applications such as LCD television, LCD screen of mobile phones, laptop computers, TFT monitors of desk top computers, large display boards in airports/railway stations/ public places etc. newlineLiquid crystals can be broadly classified into thermotropic, lyotropic and metallotropic phases. This classification is based on the processes through which the intermediate phases are achieved. Both the thermotropic and lyotropic liquid crystals consist of organic molecules. The formation of the thermotropic liquid crystal occurs when a solid is heated or an isotropic liquid is cooled. Thermotropic liquid crystals are single component systems that show mesomorphic behavior in a definite temperature range. On the other hand, the mesomorphic behavior of the lyotropic liquid crystals is exhibited in solution and depends on the influence of the solvents on solids or liquids. The constituent units of the thermotropic liquid crystals are either anisotropic molecules or associated groups of many molecules.