الفهرس 
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Abstract
Since the discovery of liquid crystals in 1888(1), several thousand compounds with liquid crystalline phases are presently known(2), and large number of papers have been published on the chemical and physical properties of liquid crystalS Liquid crystals are a Class of materials which exhibit a fourth thermodynamic state. The thermotropic liquid crystals are characterized by a temperature range and a degree of molecular ordering which is between the solid and isotropic liquid ranges • Liquid crystals are so-called because they exhibit some properties of the liquid and some properties of the solid crystalline state. In other words the liquid crystalline state represents a state of matter in which the degrees of molecular order.