Structure of materials

Structure of materials

1. Arrangement of particles

   • The properties of solid materials depend on how the particles in these materials are arranged, and how they are held together.
   • A solid melts when the forces between its particles are broken. This requires energy.
   • 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
     • the higher the melting point of the solid.

2. Modifying polymers

   • Different polymers have different properties, depending on the small molecules they were made from. But the properties of a polymer can also be change
   • Polymer chains
     • 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
     • 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
   • Plasticisers
     • Plasticisers are small molecules that can be added to polymers during their manufacture.
     • They push the polymer molecules slightly further apart, weakening the forces between them and making the material softer and more flexible.
     • 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
   • Cross-links
     • Chemical bonds can be formed to link together the chains of some polymers. These cross-links make the material tougher and less flexible.

3. Different properties of polymers- Higher tier

   • Low-density polyethene
     • Some polymer chains have side branches. Low-density polyethene (LDPE) is like this.
     • The side branches stop the polymer molecules from lining up regularly. Its structure is not crystalline.
       • This means that:
         • the material has a lower density than HDPE
         • the forces of attraction between polymer
         • molecules are weakened
         • the material is less strong, and has a lower melting point, than HDPE
   • High-density polyethene
     • high-density polyethene (HDPE) does not have side branches.
     • The polymer molecules line up regularly to give a crystalline structure.
       • 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.
   • Various amounts of crystallinity
     • By carefully controlling the amount of branching, it is possible to make polymers with various amounts of crystallinity
       • This means it is possible to make a polymer with the exact properties that are required for a particular purpose.