Dr. S. B Maulage Dept of Chemistry

LIQUID STATE Liquid Crystals

Introduction The discovery of the liquid crystal happened over a century and since this time the 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 also give illustrations of liquid crystals from the micro perspective.

liquid crystals Liquid crystals form from organic compounds and is considered as one of the phases of matter i.e. phase between the solid and liquid state of a crystal. This was discovered in 1888 by Austrian chemist Frederich Reinitzer.

Phases

Nematic Phase Molecules in nematic phase are long and rod-like in shape. They are free to move in 3D space.

Chiral Nematic This phase is consist of nematic molecules in a helical structure. The distance that it takes for the molecules to complete one turn is called the pitch. λ = n*p*cosθ

Smectic Phase Smectic phase can be obtained at lower temperatures than the nematic phase. Molecules arrange themselves in layers.(They are confined to their plane.) More order and higher viscosity

Effects of Electric field If an electric field is applied to a liquid crystal the molecules will arrange in the same direction as the field.

Twisted Nematic Liquid Cryastal This is called the twisted nematic liquid crystal and the spacing between the planes change with temperature. The spacing is associated with the wavelengths of light.

Applications of Liquid Crystals Flat screen television Wristwatches Laptop screens Digital clocks Thermometers Switchable windows

Conclusion We know today that many chemical compounds can exist in the liquid crystal state, such as cholesteryl benzoate. Thanks to the scientists that worked so diligently toward understanding this phenomenon, the world can focus on ways to make this product useful in society. Over the last century many applications such as the detection of hot points in microcircuits, the findings of fractures or tumors in humans and the conversion of infared images have become accessible due to the understanding of pitch in a liquid crystal.

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