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Kevlar is an example of a lyotropic liquid crystal. Outline what is meant by lyotropic liquid crystal.

Important Questions on Materials

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Detergents are one example of lyotropic liquid crystals. State one other example of a lyotropic liquid crystal and describe the difference between lyotropic and thermotropic liquid crystals.
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Name a thermotropic liquid crystal.
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Liquid-crystal displays are used in digital watches, calculators, and laptops. Explain the liquid-crystal behaviour of the thermotropic liquid crystal named in part (a), on the molecular level.
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Describe the meaning of the term liquid crystals. State and explain which diagram in figure 11, a or b, represents molecules that are in a liquid crystalline phase.

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Distinguish between thermotropic and lyotropic liquid crystals and state one example of each type.
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The structure of 4-pentyl-4-cyanobiphenyl, a commercially available nematic crystalline material used in electrical display devices, is shown in figure 12.

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Describe and explain in molecular terms the workings of a twisted nematic liquid crystal.

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IMPORTANT

Compare the positional and directional order in a crystalline solid, a nematic phase liquid crystal, and a pure liquid. Show your answer by stating yes or no in a copy of table 1.

  Crystalline Solid Nematic phase liquid crystal Pure liquid
Positional order      
Directional order      

 

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Outline any two principles of a liquidcrystal display device.