Structure of materials

Arrangement of particles
1. The properties of solid materials depend on how the particles in these materials are arranged, and how they are held together.
2. A solid melts when the forces between its particles are broken. This requires energy.
3. he stronger the forces between the particles, the more energy is needed to break the particles out of the solid structure. The more energy that is nee
  1. the higher the melting point of the solid.
Modifying polymers
1. Different polymers have different properties, depending on the small molecules they were made from. But the properties of a polymer can also be change
2. Polymer chains
  1. Many polymers, such as polyen, contain long molecules that lie side by side. These can uncoil and slide past each other, making the material flexliabl
  2. Long polymer chains have stronger forces of attraction than shorter ones. By making the chains of a polymer longer, a stronger and less flexible mater
3. Plasticisers
  1. Plasticisers are small molecules that can be added to polymers during their manufacture.
  2. They push the polymer molecules slightly further apart, weakening the forces between them and making the material softer and more flexible.
  3. 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
4. Cross-links
  1. Chemical bonds can be formed to link together the chains of some polymers. These cross-links make the material tougher and less flexible.
Different properties of polymers- Higher tier
1. Low-density polyethene
  1. Some polymer chains have side branches. Low-density polyethene (LDPE) is like this.
  2. The side branches stop the polymer molecules from lining up regularly. Its structure is not crystalline.
    1. This means that:
      1. the material has a lower density than HDPE
      2. the forces of attraction between polymer
      3. molecules are weakened
      4. the material is less strong, and has a lower melting point, than HDPE
2. High-density polyethene
  1. high-density polyethene (HDPE) does not have side branches.
  2. The polymer molecules line up regularly to give a crystalline structure.
    1. This means that:
      1. the material has a higher density than LDPE
      2. the forces of attraction between polymer molecules are strong
      3. the material is stronger, and has a higher melting point, than LDPE.
3. Various amounts of crystallinity
  1. By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity
    1. This means it is possible to make a polymer with the exact properties that are required for a particular purpose.

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