Liquid Crystalline System (original) (raw)

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INTRODUCTION: a) History In 1888, Austrian botanical physiologist Friedrich Reinitzer, working at the Karl-Ferdinands-Universität, examined the physico-chemical properties of various derivatives of cholesterol which now belong to the class of materials known as cholesteric liquid crystals. Previously, other researchers had observed distinct color effects when cooling cholesterol derivatives just above the freezing point, but had not associated it with a new phenomenon. Reinitzer perceived that color changes in a derivative cholesteryl benzoate were not the most peculiar feature. Figure 1: Chemical structure of cholesteryl benzoate molecule He found that cholesteryl benzoate does not melt in the same manner as other compounds, but has two melting points. At 145.5 °C (293.9 °F) it melts into a cloudy liquid, and at 178.5 °C (353.3 °F) it melts again and the cloudy liquid becomes clear. The phenomenon is reversible. Seeking help from a physicist, on March 14, 1888, he wrote to Otto Lehmann, at that time aPrivatdozent in Aachen. They exchanged letters and samples. Lehmann examined the intermediate cloudy fluid, and reported seeing crystallites. Reinitzer's Viennese colleague von Zepharovich also indicated that the intermediate "fluid" was crystalline. The exchange of letters with Lehmann ended on April 24, with many questions unanswered. Reinitzer presented his results, with credits to Lehmann and von Zepharovich, at a meeting of the Vienna Chemical Society on May 3, 1888. [1] By that time, Reinitzer had discovered and described three important features of cholesteric liquid crystals (the name coined by Otto Lehmann in 1904): the existence of two melting points, the reflection of circularly polarized light, and the ability to rotate the polarization direction of light. After his accidental discovery, Reinitzer did not pursue studying liquid crystals further. The research was continued by Lehmann, who realized that he had encountered a new phenomenon and was in a position to ABSTRACT Liquid crystaline system is a thermodynamically stable phase which is characterized by anisotropy. LC's are also termed as mesophase as they exhibit isotropic properties and fluid-like behavior under some conditions (change in temperature). LC'S are influenced by number of factors such as concentration, temperature, pH, and presence of salt. Liquid crystals are divided on the basis of shape of the molecules into two groups one is calmitic and other is discotic. The various liquid-crystal phases (called mesophases) can be characterized by the type of ordering. The ordering of liquid crystalline phases is extensive on the molecular scale. The Liquid Crystals are the only holistic representations of the mineral kingdom and most potent form of crystalline energy on earth. Liquid crystal technology has had a major effect many areas of science pharmacy and engineering, as well as device technology. Liquid crystals have a multitude of other uses. They are used for non destructive mechanical testing of materials under stress. As new properties and types of liquid crystals are investigated and researched, these materials are sure to gain increasing importance in industrial and scientific applications such as optical imaging.