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Liquid Crystals: A Fascinating State of Matter
- 3. LEARNING OBJECTIVES History The structures of liquid crystals The different types of liquid crystal and their arrangement Properties of liquid crystal Applications of liquid crystals Conclusion
- 4. States of matters Solid Liquid Gas Liquid crystals
- 5. Solid All solids have fix shape, fix volume, ductile and high melting and boiling point. It is due to solids have high attractive forces among the atoms and molecules which holds the atoms together.
- 6. Liquid Attractive forces between the molecules is weak as compared to the solid but strong as compare to gas. The molecules of liquids have more empty spaces as compare to the solid, moves around each other but molecules remain close to each other so fluid do not have fix shape and adapted the shape of container.
- 7. Gas Gases have less attractive forces among the molecules. The molecules are far away from each other. Gases move randomly so the molecules of gas will expand and fill the container.
- 8. Liquid crystals A liquid crystal is a phase between solid and liquid states(phases). Liquid Intermediate Phase Crystal Hea t Cool Melt Solidify Heat Cool
- 9. Examples
- 10. Crystals vs liquid crystals A crystal is a highly ordered structure which possesses long-range positional & orientational order. For many substances these two types of order are destroyed simultaneously when the crystal melts to form a liquid For some substances, these orders are destroyed in stages. These are liquid crystals.
- 11. A Brief History of LCs Liquid crystals was discovered by Reinitzer and Lehmann in 1888. Cholesteryl benzoate showed two melting points each. The crystal of this material melted at 145.5 ◦C into a cloudy fluid, which upon further heating to 178.5 ◦C became clear Cholesteryl benzoate 145.5 ◦C 178.5 ◦C
- 12. In 1973 the discovery of the most technological and commercial important class of liquid crystals , 4-alkyl-4-cyanobiphenyl. This material found in calculators or mobile phones.
- 14. Types of liquid crystals
- 15. Structural phases of liquid crystals Nematic drived from the Greek word, ‘nema’ which means “thread”. No positional order Molecules in same direction When temperature is increases molecules will be allign immediately In nematic crystal phase molecules are arranged parallel Nematic
- 16. Nematic liquid crystals are widely used in electro-optic display devices The classical examples of LC displaying a nematic phase is the Cyanobiphenyl
- 17. Sematic Sematic phase occurs at temperature below nematic or cholesteric. Molecules allign themselves approximately parallel & tend to arrange in layers. Chiral sematic C liquid crystals are useful in LCDs
- 18. Cholesteric The first liquid crystal Cholesteric that was observed through a polarising microscope is cholesteryl benzoate. Thus, CHOLESTERIC liquid crystal OR chiral nematic liquid crystal E.g. cholesteric benzoate: LC 145C, isotropic 178C Cholesteric liquid crystals have great potential uses as Sensors Thermometer Fashion fabrics that change colour with temperature Display devices
- 19. Properties of liquid crystals Liquid crystal can flow like a liquid, due to loss of positional order. Liquid crystal is optically birefringent, due to its orientational order Transition from crystalline solids to liquid crystals caused by a change of temperature – gives rise to THERMOTROPIC liquid crystals. Substances that are most likely to form a liquid crystal phase at a certain temperature are molecules that are ELONGATED & have some degree of RIGIDITY.
- 20. Applications Liquid crystals can be found in the following devices: Digital watches Pocket TVs Gas pumps Parking meters Thermal imaging Cell phones Helmets and bullet-proof jacket Digital signs Electronic games calculators
- 21. Conclusion We know today that many chemical compounds can exist in the liquid crystal state, such as cholesteryl benzoate. The world can focus on ways to make this product useful in society. Over the last century many applications such as the detection of hot points in microcircuits, the findings of fractures or tumors in humans and the conversion of infrared images have become accessible due to the understanding of pitch in a liquid crystal.