C.6 Liquid Crystals The liquid crystal state Liquid Crystal Examples 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

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

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.

Practice Exercise Pg. 322, visuals of molecules

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.

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.

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

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

Examples of Nanotech Carbon nanotubes Buckminsterfullerene (bucky ball): C60 Led to development of “nanotubes”

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

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

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.

Practice Exercise: A carbon nanotube has a diameter of 1 nm and is 10 µm long. How may diameters does this length represent? These tubes are believed to be stronger than steel. Explain the tensile strength of the tubes on a molecular level. 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. 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.