ABSTRACT
The Austrian botanist Friedrich Reinitzer, who studied the function of cholesterol in plants, discovered in 1888 that a cholesterol benzoate crystal, when heated, does not melt like an ordinary crystal but turns at 145°C into a milky liquid, which becomes perfectly clear at 178.5°C. The observation of a nematic liquid crystal between cross-polarizers, a texture formed by black filaments which are singular lines of molecular alignment corresponding to the light extinction positions, connected together by nuclei. Liquid crystal phases are often obtained with elongated molecules consisting of a central rigid stick-shaped part that promotes the order of orientation and flexible ends preventing crystallization and promoting the liquid state. Thermotropic liquid crystals are observed by varying the temperature. Twisted nematics are used in almost all common liquid crystal displays. Defects in crystals are called dislocations. The defects in liquid crystals are called disclinations. The microscopic image of these defects is called a texture.
