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    5 5 Presentation Transcript

    • Types of Structure
      • When a liquid cools it solidifies
      • The resulting solid may have an orderly structure CRYSTALLINE or POLY-CRYSTALLINE
      Orderly ‘Crystalline’ Structure Shows some irregularity or ‘Poly-Crystalline’ Structure
    • Cooling and Crystal Size
      • Quick cooling results in _________ crystals
      • Slow cooling results in ________ crystals
      SMALL LARGE
    • Non-Crystalline Structures
      • If no orderly structure is present, this is called AMORPHOUS.
      • It is a random structure and this gives it different properties – but what are they..?
    • Amorphous Structures
      • Molecules are arranged randomly – but some regions align…
        • For plastics this gives them extensibility (non reversible)
        • For elastic behaviour in things like rubber, the molecules rotate. This is reversible
    • Plastic behaviour of partly amorphous structure
    • Modelling Amorphous Structures
      • Use spaghetti to model amorphous structures
      • Does a yoghurt pot give any indication that it is made of long chain molecules?
    • Elastic (e.g. Rubber)
    • Young’s Modulus – Amorphous Structures
      • Draw the graph that you think you would get for Stress/Strain for a rubber band
      Strain Stress
    • Young’s Modulus – Amorphous Structures
      • Draw the graph that you think you would get for Stress/Strain for a rubber band
      Strain Stress Molecules ‘lining up’ Molecules fully extended – Less flexible
    • Making Rubber Stiffer
      • Why is some rubber stiffer than other rubber?
      • Would you use the same type of rubber for a car tyre as for a pencil eraser?
    • Vulcanisation
    • Types of Rubber
      • Natural Rubber Vulcanised Rubber
      Stretched Vulcanised Rubber