Understandings:
- Liquid crystals are fluids that have physical properties (electrical, optical and elasticity) that are dependent on molecular orientation to some fixed axis in the material.
- Thermotropic liquid-crystal materials are pure substances that show liquid- crystal behaviour over a temperature range.
- Lyotropic liquid crystals are solutions that show the liquid-crystal state over a (certain) range of concentrations.
- Nematic liquid crystal phase is characterized by rod shaped molecules which are randomly distributed but on average align in the same direction.
Applications and skills:
- Discussion of the properties needed for a substance to be used in liquid-crystal displays (LCD).
- Explanation of liquid-crystal behaviour on a molecular level.
Guidance:
- Properties needed for liquid crystals include: chemically stable, a phase which is stable over a suitable temperature range, polar so they can change orientation when an electric field is applied, and rapid switching speed.
- Soap and water is an example of lyotropic liquid crystals and the biphenyl nitriles are examples of thermotropic liquid crystals.
- Liquid crystal behaviour should be limited to the biphenyl nitriles.
- Smectics and other liquid crystals types need not be discussed.
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International-mindedness:
- The production of many electronic goods is concentrated in areas of the world where the working conditions may not be ideal. Should there be internationally set labour standards for all workers? What implications would this have on the cost of consumer goods?
Theory of knowledge:
- Developments in technology mean that we can store more and more information available on an increasingly smaller scale. Does this mean that we can access more knowledge?
Utilization:
- Syllabus and cross-curricular links:
- Topic 20.3—chirality and stereoisomers
Aims:
- Aim 6: Experiments could include investigating a thermotropic liquid crystal and the temperature range which affects these crystals.
- Aim 7: Computer animations could be used to investigate thermotropic liquid crystals.
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