Thermotropic temperature dependent Lyotropic concentration dependent Metallotropic Nematic Smectic Cholesteric Various forms depending on concentration Thermotropic Liquid Crystals ID: 554130
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Slide1
Liquid Crystals
Thermotropic
(temperature dependent)
Lyotropic (concentration dependent)
Metallotropic
Nematic
Smectic
Cholesteric
Various forms depending on concentrationSlide2
Thermotropic
Liquid Crystals
Rigid Core
Flexible Tails
Rod shaped moleculeSlide3
Liquid Crystals are a Phase
For some molecules, there are extra steps in the phase change between solid and liquid.
Increase in temperature. Decrease in order.
Smectic
Nematic
Crystalline
Liquid
Liquid CrystallineSlide4
Smectic
Liquid CrystalsLess ordered than a crystalline solid.Molecules have orientational
order (they are all “facing” in about the same direction).Molecules are in layers (some positional order, but they behave like liquids (i.e. can move around) within these layers.Slide5
Nematic
Liquid CrystalsLess ordered than smectic phase and crystalline solid.
Molecules have orientational order (they are all “facing” in about the same direction).Molecules have no positional order (there are no layers).Slide6
Liquid Crystal Displays
Use “twisted” nematic phase.Liquid crystals form a helical twist as a result of perpendicular directors (
polarising filters).Liquid crystals act a guide for polarised light.
http://youtu.be/O3aITfU_UvESlide7
Cholesteric
Phase(aka Chiral Nematic)Some types of
nematic liquid crystals spontaneously arrange themselves into a spiral arrangementThe molecules have a nematic arrangment within each layer.Slide8
Cholesteric
Liquid Crystals and TemperatureThe distance for a full twist in the helix is call the “pitch”.Cholesteric liquid crystals reflect light approx. equal to the pitch.
The pitch depends on temperature.At lower temp thepitch is longer.Slide9
Effect of Phase on Opacity