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

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