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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

http://en.wikipedia.org/wiki/Image:Shilirren_texture.jpg

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Nematic Phase

Molecules in this phaseare long and rod-like inshape. They are free tomove in space.

http://en.wikipedia.org/wiki/Image:Shilirren_texture.jpg

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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

http://www.lci.kent.edu/fcd.html

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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

http://shopper.howstuffworks.com/products/Hewlett+Packard+f2105+%28Black%2C+Silver%29+21+inch+LCD+Monitor/SF-1/PID-25727430

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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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