C.6 Liquid Crystals

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C.6 Liquid Crystals

• The liquid crystal state
• Intermediate state of matter with properties
  between the solid and liquid state. (nematic
  state)
• Share many physical properties with solid
  crystals, but properties can be easily modified.
• Typically made up of long polar organic
  molecules.
• Liquid Crystal Examples
• Graphite, cellulose, DNA, spider silk solution

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Liquid Crystal State

• Thermotropic liquid crystals
• formed by pure substances over a certain
  temperature range.
• Lyotropic liquid crystals
• Formed by solutions
• Properties determined by both temperature and
  concentration.
• Soap example, pg 321

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LCD devices

• Often use polar molecules
• Ability to transmit light depends on relative
  orientation of molecules.
• Orientation of molecules controlled by
  application of an electric field (voltage)
• Common molecule pentylcyanophenyl
• Chemically stable
• Liquid crystal phase over suitable range of
  temperatures.
• Polar, orientation easily affected by electric
  field.
• Responds to changes of voltage quickly.

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Practice Exercise

• Pg. 322, visuals of molecules

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C.7 Nanotechnology

• The research and technology development in the
  1-100 nm range.
• the science of the very small with big
  potential
• Interdisciplinary, involving chemistry, physics,
  biology, and materials science.

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Producing Nanomaterials

• Top-down approach
• Start with a bulk material and break it down into
  smaller materials.
• Bottom-up approach
• Build the material from atomic or molecular
  species.

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Properties of Nanomaterials

• Very different from their bulk/macro-level
  properties.
• Quantum effects play large role.

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Examples of Nanotech

• Scanning Tunneling Microscope (STM)
• use of ultra fine atomic probe that feels the
  surface of a material rather than sees it.

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Examples of Nanotech

• Carbon nanotubes
• Buckminsterfullerene (bucky ball) C60
• Led to development of nanotubes

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Implications of Nanotech
Current Potential Uses
Agriculture Nanoporous zeolites for slow release of water and fertilizers
Healthcare/medicine Biological nanosensors as diagnostic tools
Energy Nanoscale catalyst-enhanced fuels for better efficiency nanomaterials for fuel cells/batteries/solar cells.
Electronics Carbon nanotube electronic components
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Implications of Nanotech
Current Potential Uses
ICT Flat panel flexible displays using nanotechnology high-density data storage using nanomagnetic effects faster processing using quantum computers.
Water treatment Nanomembranes for water treatment
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Implications of Nanotech

• Possible concerns
• Unknown health effects, immune systems
• Toxicity
• Reactivity and kinetics
• Scientists must be responsible to trial test new
  substances, assess the risks, and engage in
  debate with the public to address facts and
  communicate issues.

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Practice Exercise

1. A carbon nanotube has a diameter of 1 nm and is
   10 µm long. How may diameters does this length
   represent?
2. These tubes are believed to be stronger than
   steel. Explain the tensile strength of the tubes
   on a molecular level.
3. One problem in the synthesis of nanotubes is that
   a mixture of tubes with different lengths and
   orientations is produced. Suggest why this is a
   problem.
4. The wavelength of UV light is in the range 1-400
   nm. Many modern sunscreens contain nano-sized
   particles of titanium dioxide which do not absorb
   ultraviolet radiation. Suggest how these
   nono-particles are able to protect skin from UV
   radiation.