Smart materials behave differently depending on the conditions. e.g. temperature.
Shape memory alloys can return to their original shape after being deformed.
Nitinol is a shape memory alloy.
When cool you can bend it and twist it like rubber
However if you bend it too far, it will stay bent.
If you heat it above a certain temperature, it will return to its original shape.
Nitinol is used in glasses frames and dental braces. In the mouth it warms up and tries to return to its original shape, so gently pulls the teeth with it.
- Nanoscience refers to structures that are 1-100nm in size, of the order of a few hundred atoms, and is the use of nanoparticles
- Nanoparticles are tiny particles.
- Many new nanoparticles are being developed
- Nanoparticles have very different properties to the same materials in bulk.
- Nanoparticles have a high surface area to volume ratio = new industrial catalyst
Other new uses:
- New computers
- Highly sensitive sensors to detect one type of molecule - test water purity
- Stronger and lighter construction materials
- New cosmetics such as suncream and deodorant that do their job without leaving marks on the skin.
- New lubricant coatings using fullerenes - reduce friction in artificial joints and gears
- Nanomedicine uses fullnerenes that are absorbed more easily by the body than most particles, delivering drugs into cells where they are needed.
- Nanotubes conduct electricity - so can be used in tiny electric circuits for computer chips
Forces between molecules determine the properties of plastics.
All plastics have strong covalent bonds holding the atom together in long chains.
- Consist of individual tangled polymer chains, held together by weak intermolecular forces. Which are free to slide over each other.
- Thermosoftening polymers consist of individual tangled polymer chains, The forces between the chains are easy to overcome, so they have low melting points. This allows them to be melted and remoulded.
- Consist of polymer chains with cross-links between them so they have strong intermolecular forces, that hold the chains firmly together.
- Thermosetting polymers consist of polymer chains with cross-links between them so they do not melt when they are heated. They are strong, hard and rigid.
The properties of polymers depend on what they have been made from and the conditions under which they are made.
Low Density (LD) polyethene:
- Made by heating polyethene to about 200'C under high pressure.
- It's flexible and is used for bags and bottles
High Density (HD) polyethene:
- Made at a low temperature and pressure in the presence of a catalyst.
- It's more rigid and is used for water tanks and drainpipes.
Use of Plastics
The use of a plastic depends on its properties:
- Cost to produce
- Resistance to chemicals
- Melting Point
- Ability to be made into fibres