OCR 21st Century C2

Material Choices
1. Nanotechnology
  1. use and control of structures that are very small (1 to 100 nanometres in size)
    1. Naturally- Seaspray, Geckos feet
      1. Accident- smallest particulates from combustion of solid fuels
    2. By design
      1. nanoparticles can be used to modify the properties of materials,
        the use of silver nanoparticles to give fibres antibacterial properties
        adding nanoparticles to plastics for sports equipment to make them stronger
    3. nanoparticles of a material show different properties compared to larger particles of the same material, and that one of the reasons for this is the much larger surface area of the nanoparticles compared to their volume
      1. As nano-particles display different properties to their larger particles, the concern is that they may be damaging to our health e.g. get into our brain via our bloodstream. However, not enough is known yet
Materials
1. Natural
  1. wool, silk, cotton, latex, fur and paper are obtained or made from living things
2. - chemicals or mixtures of chemicals, and include metals, ceramics and polymers
3. Synthetic materials are alternatives and are made from crude oil
Crude Oil
2. crude oil consists mainly of hydrocarbons, which are chain molecules of varying lengths made from carbon and hydrogen atoms only
  1. small percentage of crude oil is used for chemical synthesis and that most is used as fuels
    1. Longer chained molecules have greater melting and boiling points due to the fact that more energy is required to break the intermolecular forces and change its state
      1. smaller molecules have weaker intermolecular forces which can be overcome with less energy.
        Fractional distillation separates the various hydrocarbon compounds. Crude oil needs to be refined into useful products
        Smaller molecules rise because they have weak intermolecular forces and so little energy is required to break the molecules and change the oil to a gas
        Larger molecules have stronger intermolecular forces
        Despite this, the intramolecular forces (covalent bonds between atoms) don't break.
        They are far too strong
Polymers
1. monomers can join together to make very long molecules called polymers, and that the process is called polymerisation
  1. Polymers are plastics
    1. Polythene (Polyethene)
      1. Low-density polyethene molecules have a jumbled amorphous structure. This means that the material has a lower density than HDPE; the intermolecular forces obetween polymer molecules are weakened; the material is less strong, and has a lower melting point, than HDPE.
        High-density polyethene (HDPE) does not have side branches and is crystalline as the molecules line up regularly. This means that: the material has a higher density than LDPE; the forces of attraction between polymer molecules are strong; the material is stronger, and has a higher melting point, than LDPE.
      2. Synthetic alternatives tend to be lighter, more durable, water-resistant and often cheaper
        PVC replaced wood in window frames. Weather resistant, strong and durable
    2. Nylon (replaced silk)
    3. Neoprene
    4. cotton
    5. silk
    6. wool
  2. If the polymer chains are packed close together, the material will have a HIGH DENSITY
Strength- resisting a force
1. Tensile- resistance to a pulling force. E.g. cables/ropes
2. Compressive- resistant to a pushing force. E.g. bricks
Stiffness- ability to bend (rubber is strong but can be bent)
Hardness- difficulty to be cut
Density- mass per unit volume.
1. Objects less dense than water float e.g. ice
  1. Objects more dense than water sink
Increased Chain length
1. Longer chains are stiffer and have higher melting points due to the fact that they have strong intermolecular forces. It is harder for longer chains to slide over each other
Cross linking
1. Chemical bonds can be formed to link together the chains of some polymers. These cross-links make the material stiffer, stronger and more heat resistant. This is because it becomes very difficult to overcome the extremely strong intermolecular forces, therefore a higher MP and BP is required
  1. E.g. sulfur
Plasticicsers
1. Plasticisers are small molecules that can be added to polymers during their manufacture.
  1. Unplasticised PVC, usually called uPVC, is hard. It is used for pipes and window frames. Plasticised PVC is soft. It is used for clothing and flooring.
  2. They push the polymer molecules slightly further apart, weakening the forces between them and making the material softer and more flexible. as the chains can slide over each other
Crystallinity-
1. A crystalline polymer has straight chains with no branches decreasing the distance between chains

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OCR 21st Century C2

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	Erstellt von Pritesh Patel vor fast 9 Jahre