Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

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Summary

You should now be familiar with the following concepts:

  • Above Tg polymers are rubbery, whereas below Tg they are glassy

  • Rubbery behaviour arises from the polymer's ability to change its conformation at high temperatures

  • Glassy behaviour arises from the polymer's lack of ability to change its conformation at low temperatures

  • Many factors affect the Tg of a polymer. Some factors are to do with the chemistry of the polymer:

    • chain length
    • chain flexibility
    • side groups
    • branching
    • cross-linking
    • the presence of plasticisers

    Other factors are to do with the method of measuring Tg:

    • strain rate
    • cooling or heating rate
     
  • You should also understand the theory of kinetics, which explains how glasses form and noted that there are many different experimental methods for measuring the glass transition temperature in polymers.

  • Finally you should have observed how the behaviour of a rubber ball varies when it is bounced above, below and near its Tg and seen how the behaviour of silly putty varies at different strain rates.