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LIQUID CRYSTALS Introduction What are Liquid crystals ? Its History & Discovery Any of various liquids in which molecules are regularly arrayed like a solid crystal along one or two dimensions, but are free in the other dimensions as with typical liquids. Liquid crystals often display unusual and often manipulable optical properties such as anisotropic scattering. They can be divided into two classes, Thermo tropic(nematic, chiral nematic, and smectic. ) and Lyotropic.

Transitions to thermotropic phases are initiated by changes in temperature, while those to lyotropic hases can also be initiated by changes in concentration. The Discovery, March 1, 1888 Friedrich Reinitzer, a plant physiologist at the Charles University, in Prague, notices that the plant derivative cholesteryl benzoate has two melting points. New Compounds Identified, 1889 ??” 1908 European scientists identify more than 200 compounds exhibiting liquid crystal behavior, but no commercial uses are found.

Flowing Crystals Get Their Name , January 1, 1889 Otto Lehmann, a physical chemist working in Aachen, Germany, publishes an article on what he terms fliessende Krystalle, or “flowing crystals,” noting that within a certain emperature range cholesteryl benzoate pours like a liquid but refracts polarized light like a crystalline solid. Three Classes of Crystal, November 1, 1922 French crystallographer Georges Friedel publishes an article in which he divides liquid crystals into three categories based on their molecular organization: nematic, smectic, and cholesteric.

Recent Developments Nematic Liquid Crystal Confined in Electrochemically Etched Porous Silicon: Optical Characterization and Applications in Photonics. Liquid Crystals into Planar Photonic Crystals . Manipulating Nematic Liquid Crystals-based Magnetophotonic Crystals. A New Method of Generating Atmospheric Turbulence with a Liquid Crystal Spatial Light Modulator. Three Dimensional Temperature Distribution Analysis of Ultrasound Therapy Equipments Using Thermochromic Liquid Crystal Films .

Simple Optical Methods for Measuring Optical Nonlinearities and Rotational Viscosity in Nematic Liquid Crystals. A Polarizer-free Liquid Crystal Display using Dye-doped Liquid Crystal Gels . Active-Matrix Liquid Crystal Displays – Operation, Electronics and Analog Circuits Design. TET-LCD Driver IC Design 171 . ACF Curing Process Optimization for Chip-on-Glass (COG) Considering Mechanical nd Electrical . Properties of Joints. Introduction to LED Backlight Driving Techniques for Liquid Crystal Display Panels. Optoelectronic Device using a Liquid Crystal Holographic Memory.

Applications Liquid crystal technology has had a major effect many areas of science and engineering, as well as device technology. Applications for this special kind of material are still being discovered and continue to provide effective solutions to many different problems. Oanuary 1, 1950 ??” January 1, 1959) An Early Application , Scientists try using color- changing cholesteric compounds as temperature sensors. In March 1960 James Fergason and two colleagues at Westinghouse Electric Corp. , in Pittsburgh, apply for a U. S. atent for “thermal imaging devices utilizing a cholesteric liquid crystalline phase material. ” (April 1, 1962) RCA Research Begins, RCA physical chemist Richard Williams begins studying the electro-optic behavior of liquid crystals. Several months later he observes acrinkling effect in a liquid crystal sample; in November he applies for a patent to incorporate the effect into electronic displays. (May 1, 1965 )Dynamic Scattering Observed , George Heilmeier observes dynamic cattering in liquid crystals, which becomes the focus of RCA’s LCD investigations.

Over the next several years, the group succeeds in synthesizing room-temperature liquid crystals and builds several prototype LCDs, including an electronic clock and a cockpit display. Modern applications Liquid Crystal Displays (LCDs. ) Liquid Crystal Thermometers Optical Imaging They are used for nondestructive mechanical Helmets and Bullet proof vests Battery testing strips (used in Duracell) Slugs and Snails -Nature beat us to the punch in making use of liquid crystals. The ucus secreted by slugs behaves like liquid crystals.

Conclusion Today several compounds exist in liquid crystal state , such as cholesteryl benzoate. A endless gratitude to the scientists who worked on deligently towards understanding this phenomenon, so now we can focus on the ways to make this product useful to the society. Over the past century many applications such as detection of hot points in microcircuits , the detection of fractures and tumors in humans and the conversion of infrared images has become accessible due to the understanding of pitch in a crystal.

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