williams liquid crystals
TRANSCRIPT
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Liquid Crystals
Danielle WilliamsDept of Physics
University of Texas at Arlington
http://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.htmlhttp://www.lci.kent.edu/batonnets.html -
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Introduction
Liquid crystals are very important in the study of optics,chemistry and polymer science. The discovery of theliquid crystal happened over a century and since this timethe phenomena has been applied to many products in our society. This presentation will cover the properties,different phases and uses of liquid crystals. It will alsogive illustrations of liquid crystals from the micro
perspective.
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What are liquid crystals ?Liquid crystals form from organic compounds and is
thought of as the phase of matter between the solid andliquid state of a crystal.This phenomena was discovered in
1888 by Austrian chemist Frederich Reinitzer.
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Phases
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Nematic Phase
Molecules in this phaseare long and rod-like inshape. They are free tomove in space.
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Chiral Nematic
This phase iscomposed of nematic
molecules in a helicalstructure about thelayer normal.
The distance that ittakes for the moleculesto complete one turn iscalled the pitch.
= n*p*cos
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Smectic Phase
This phase can bereached at lower temperatures than thenematic phase.
Molecules alignthemselves in layers.(They are restricted totheir plane.)
More order and higher viscosity
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Columnar Phase
Characterized by its stacked columns of molecules.
Discovered in 1977 by Chandrasekhar
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Order Parameter S =
The order parameter in a liquid crystalrange from 0.3 to 0.9
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Electric field Effects
If an electric field isapplied to a liquid
crystal the moleculeswill align in the samedirection as the field.
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Twisted Nematic
This is called thetwisted nematic liquid
crystal and the spacing between the planeschange withtemperature. The
spacing is associatedwith the wavelengthsof light.
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Uses of Liquid Crystals
Flat screen television Wristwatches Laptop screens Digital clocks
Thermometers Switchable windows
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Conclusion We know today that many chemical compounds can
exist in the liquid crystal state, such as cholesterylbenzoate. Thanks to the scientists that worked sodiligently toward understanding this phenomenon, theworld can focus on ways to make this product useful insociety. Over the last century many applications suchas the detection of hot points in microcircuits, thefindings of fractures or tumors in humans and theconversion of infared images have become accessibledue to the understanding of pitch in a liquid crystal.
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