Liquid crystals

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Liquid crystals (LCs) are a state of matter that have properties between those of a conventional liquid and those of a solid crystal .

Transcript of Liquid crystals

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Liquid crystals (LCs) are a state of matter that have properties between those of a conventional liquid and those of a solid crystal.

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Yerra BharathG V S R Pavan Kumar

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History In 1888, Austrian botanical

physiologist Friedrich Reinitzer, examined that Cholesteryl benzoate had two distinct melting points. 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.

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vs.vs.

AnisotropicAnisotropic

Liquids and gases(uniform properties in all

directions).

Liquid Crystals have orientational order

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Liquid crystals are highly anisotropic fluids that exists between the solid and liquid phases.

This dual physical properties is referred to as mesomorpism.

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Characteristics of liquid crystals

1. Positional order2. Orientational order3. Bond orientational order

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The orientation of Liquid Crystals can be affected by…

Pressure Temperature Electrical Field

S. Palmer, LCTec Displays, Inc. 2005

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Classification Based on breaking order of the

solid state

1. Thermotropic liquid crystals

2. Lyotropic liquid crystals

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Thermotropic phases are those that occur in a certain temperature range.

Types1. Nematic2. Cholesteric (Chiral Nematic)3. Smectic

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There are 2 basic phases Nematic & Smectic

Anisotropic substances may go through one or several

Liquid Crystal Phases

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Smectic phases

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The chiral nematic phase) (left, also called the Cholesteric phase, and the smectic C* phase (right).

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The molecules in nematic structure maintain a parallel or nearly parallel arrangement to each other along the molecular axes. They move in three directions and can rotate about one axis hence the structure is one dimensional.

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Cholesteric (Chiral Nematic)

It is modification of

nematic liquid crystal because many compounds of this are derivatives of cholesterol

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p refers to the chiral pitch, is the distance it takes for the director to rotate one full turn in the helix.

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Smectic The molecules in this phase

show a degree of translational order which was not present in the nematic.

Nearly 8 to 9 smetic phases are

labeled by alphabets.

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Lyotropic liquid crystals

Structure of lyotropic liquid crystal

The red heads of surfactant molecules are in contact with waterwhereas the tails are immersed in oil (blue): bilayer (left) and micelle (right)

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A lyotropic liquid crystal exhibit liquid-

crystalline properties in certain concentration ranges.

Many amphiphilic molecules show lyotropic liquid-crystalline phase Examples: 1. Sodium laurate in water 2. Dhosphatidly Choline in water.

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The Nematic phase is most commonly The Nematic phase is most commonly used in Liquid Crystal Displays used in Liquid Crystal Displays

(LCD)(LCD)

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Computer MonitorLight Shutters

Small Displays

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Liquid Crystal Displays (LCDs)

Liquid crystal thermometers Helmets and Bullet-proof vests:

Battery testing strips (used by DuraCell)