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

Yerra BharathG V S R Pavan Kumar

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.

C

molecule

Chemical structure of Cholesteryl benzoate molecule

vs.vs.

AnisotropicAnisotropic

Liquids and gases(uniform properties in all

directions).

Liquid Crystals have orientational order

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

This dual physical properties is referred to as mesomorpism.

Characteristics of liquid crystals

1. Positional order2. Orientational order3. Bond orientational order

The orientation of Liquid Crystals can be affected by…

Pressure Temperature Electrical Field

S. Palmer, LCTec Displays, Inc. 2005

Classification Based on breaking order of the

solid state

1. Thermotropic liquid crystals

2. Lyotropic liquid crystals

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

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

There are 2 basic phases Nematic & Smectic

Anisotropic substances may go through one or several

Liquid Crystal Phases

Nematic phase

Smectic phases

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

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.

Cholesteric (Chiral Nematic)

It is modification of

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

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

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.

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)

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.

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

(LCD)(LCD)

Computer MonitorLight Shutters

Small Displays

Liquid Crystal Displays (LCDs)

Liquid crystal thermometers Helmets and Bullet-proof vests:

Battery testing strips (used by DuraCell)