LIQUID CRYSTALS WHAT ARE THEY?. STRUCTURE OF SOLIDS, LIQUIDS AND GASES All matter is made up of miniscule particles called molecules In a pure material

LIQUID CRYSTALSWHAT ARE THEY?

STRUCTURE OF SOLIDS, LIQUIDS AND GASES• All matter is made up of miniscule

particles called molecules• In a pure material these are identical• Mixtures contain different molecules• Two different types of molecules are

shown in green and blue• In a solid material, the molecules are

tightly bound in a regular 3-dimensional structure and cannot move: this is called a crystal

• In a liquid material the molecules are more loosely bound to each other, farther apart and arranged randomly, which allows them to move

• In a gas the molecules are free to zoom about with very large distances between them, although they do bounce off each other and the walls of the container.

What do you think happens if the molecules are long, like rods, and not spheres?

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RODLIKE MOLECULES

• Elongated molecules can be ordered both in their position and their orientation

• In a solid crystal, both can be ordered and the molecules are firmly bound and cannot move

• In a liquid, both can be random and the molecules are more loosely bound to each other and farther apart, which allows them to move

• In a gas the molecules are free to zoom about freely with very large distances between them and random orientations

What do you think happens in a liquid, if the molecules all point in the same direction?

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Solid

Liquid

Gas

THIS IS A LIQUID CRYSTAL

• In a liquid crystal the elongated molecules are ordered in their orientation, but may be positioned randomly

• They are loosely bound to each other and far enough apart, so they are free to move

• Liquid crystals flow freely like a liquid, but they are milky in appearance and have many of the optical properties of a solid crystal

• Solid crystals can melt to give liquid crystals, or ordinary liquids

• Liquid crystals can transform to become ordinary liquids at higher temperatures

These behaviours are illustrated in the following slides for increasing temperatures

Liquid Crystal

Solid

Liquid

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Amount of Heat

SOLID

Crystal

GlassParticles held together in

RANDOM fixed positions & orientations

Particles held together in ORDERED

fixed positions & orientations

LIQUID CRYSTAL

LIQUIDParticles held together in

movable positions & random orientations

GASParticles no longer held

together – free to move and rotateMelting/Freezing

PointClearing

PointBoiling Point

Rodlike particles held together in movable

positions & DEFINED orientations

INCREASING TEMPERATURE

TemperatureTemperature

Solid

SOLID

Crystal



Particles held together in ORDERED fixed positions &

orientations

LIQUID CRYSTAL

LIQUID

Rodlike particles held together in

movable positions & DEFINED orientations

Particles held together in movable positions & random

orientations



PointClearing

PointBoiling Point


Amount of Heat


Solid

Liquid Crystal

SOLID

Crystal




orientations

LIQUID CRYSTAL

LIQUIDParticles held

together in movable positions & random

orientations



PointClearing

PointBoiling Point




Amount of Heat


Solid

Liquid Crystal

Liquid

SOLID

Crystal




orientations

LIQUID CRYSTAL

LIQUID



Particles held together in movable positions & random

orientations

GASParticles no longer held together – free to move and rotate

Melting/Freezing Point

Clearing Point

Boiling Point


Amount of Heat


Solid

Liquid Crystal

Liquid

Gas

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LIQUID CRYSTALS WHAT ARE THEY?. STRUCTURE OF SOLIDS, LIQUIDS AND GASES All matter is made up of miniscule particles called molecules In a pure material