Advanced Topic 289 of 1102 States of Matter & Solutions
Liquid Crystals
Materials with order between liquid and crystal, used in displays.
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In-depth explanation of Liquid Crystals
Liquid crystals are phases of matter that have orientational order like a crystal while retaining the fluidity of a liquid. Their molecules are typically rod-shaped or disc-shaped and tend to align along a common direction called the director. The three main types are nematic, in which molecules align in one direction without positional order, smectic, which adds layering, and cholesteric, which has a twisted helical arrangement. Applying an electric field changes the alignment of the molecules, which alters how light passes through them. This property is used in liquid crystal displays, thermometers and optical devices.
Going deeper: Liquid Crystals
Key ideas: Transition sequence on heating: crystal, smectic, nematic, isotropic liquid, with clearing points marking each transition. Typical molecules are elongated with rigid cores, such as cyanobiphenyls. Thermotropic types respond to temperature and lyotropic types to concentration, as in soap solutions and cell membranes. Display pixels switch in milliseconds with only a few volts.
Common mistakes and connections: Students think liquid crystals are a mixture of liquid and crystal, rather than a distinct mesophase. Another error is saying all liquid crystals are nematic. Colour changes in cholesteric thermometers come from helical pitch changes with temperature. Links to intermolecular forces, polarization of light, display technology and biological membranes.
Visualization of Liquid Crystals
Liquid crystals contain elongated molecules with orientational order like a crystal but flow like a liquid, used in LCD screens. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A twisted nematic liquid crystal layer in a display rotates the polarization of light, and an electric field switches each pixel on or off.
Frequently asked questions about Liquid Crystals
What is Liquid Crystals?
Materials with order between liquid and crystal, used in displays.
Is Liquid Crystals a beginner, intermediate or advanced topic?
Liquid Crystals is a advanced topic in States of Matter & Solutions. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Liquid Crystals?
Study these earlier topics in States of Matter & Solutions first: Crystal Defects, Schottky Defect, Frenkel Defect.
What comes after Liquid Crystals?
The next topics in States of Matter & Solutions are Solution and Solute and Solvent.
Can I practise Liquid Crystals with quizzes?
Yes. The interactive lesson includes a self-check question on Liquid Crystals, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Liquid Crystals fits in States of Matter & Solutions
Liquid Crystals is topic 70 of 109 in States of Matter & Solutions.