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C6 Liquid Crystals

C6 Liquid Crystals. C.6.1 Describe the meaning of the term liquid crystals . Solid particles have an orderly arrangement in which molecules are fixed in position and orientation Liquid particles are free to move around randomly and change their orientation.

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C6 Liquid Crystals

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  1. C6 Liquid Crystals

  2. C.6.1 Describe the meaning of the term liquid crystals • Solid particles have an orderly arrangement in which molecules are fixed in position and orientation • Liquid particles are free to move around randomly and change their orientation. • However, some show properties in between the liquid and solid states. Liquid crystals have some order and some ability to move around. For example, liquid crystals can orient the molecules like a solid, but still move to different positions.

  3. C.6.2 Distinguish between thermotropic and lyotropic liquid crystals. • Thermotropic liquid crystal materials occur as liquid crystals over a certain temperature range between the solid and liquid phases. (LCD TVs, alarm clocks, etc.) • Biphenyl nitriles are commonly used as thermotropic liquid crystals.

  4. C.6.2 Distinguish between thermotropic and lyotropic liquid crystals. • Lyotropic liquid crystals show the liquid crystal state at certain concentrations. • Examples are soap solutions. At higher concentrations the soap molecules group together to form micelles.

  5. C.6.3 Describe the liquid-crystal state in terms of the arrangement of the molecules and explain thermotropicbehaviour. • As a solid, the rod shaped molecules (such as biphenyl nitriles) are fixed in position and arranged in layers. • When these are heated, the order is disrupted to form nematic liquid crystals. The layer arrangement no longer exists. However, they still point in the same direction. • With further heating, the directional order is lost as well as it moves into the liquid phase.

  6. C.6.4 Outline the principles of the liquid-crystal display device. • A polarized lens (polarizer) causes light to vibrate in only one direction. • If a second polarizer was set up perpendicular to the first, then it would block the transmission of light.

  7. C.6.4 Outline the principles of the liquid-crystal display device. • A liquid crystal can rotate the plane of light so it can pass through the second polarizer. This is due to the ability of the liquid crystal molecules to orient in a certain direction.

  8. C.6.5 Discuss the properties needed for a substance to be used in liquid-crystal displays. • Chemically stable • Liquid-crystal phase stable over a suitable range of temperatures • Polar in order to change the orientation when a electric field is applied • Rapid switching speed (Be able to orient quickly)

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