GCSE and A level chemistry exam revision notes on smart materials and some high performance polymer materials

Part 3 SHAPE MEMORY POLYMERS and pH and temperature sensitive-responsive polymers, self-healing materials

Part 3a. SHAPE MEMORY POLYMERS

• These are organic (usually) polymer materials in which deformation (change in shape) can be induced and recovered through temperature changes or stress changes.

• Shape memory polymers (SMPs) are another example of scientists trying to design 'intelligent' and 'self-repairing' materials e.g. like the development of high performance polymers and shape memory alloys.

• Thermally induced shape memory materials (like shape memory alloys, SMA) are easy to manufacture but cheaper than SMAs.

  • The basic principles of manufacture are as follows e.g. for an implant for some minimal invasive surgery procedure

    • The polymer is made and procured into the permanent shape by conventional polymerisation and processing technology.

    • This is followed by the 'programming' process which involves either (a) heating sample to deform, cooling below transition temperature, or (b) directly deforming SMP device at room temperature.

    • This then 'programmes' the polymer device to achieve its desired when activated on reaching the transition temperature.

    • Summarising ...

    • (i) polymer made into the SMP's permanent shape at 37^oC e.g. [=]

    • (ii) the SMP device compressed into temporary shape at room temperature (20-25^oC) e.g. <->

    • (iii) the SMP device undergoes transition to the required permanent shape at 37^oC e.g. back to [=]

• They are used in minimal invasive surgery procedures.

  • This can be achieved with stimuli sensitive implant materials.

  • Degradable implants could be inserted into the body in a compressed (temporary) shape, through a small incision, where they obtain the desired final relevant shape for the particular situation after warming up to body temperature i.e. the SMP device has a transition temperature above room temperature (operating theatre temperature) but below the body temperature of 37^oC e.g. 35-37^oC.

    • After some time, the implant, can be designed to then degrade away!

• SMPs have applications in high performance textiles.

• Self-repairing plastic components in technical devices.

Part 3b. pH-SENSITIVE POLYMERS

• pH-sensitive polymers are materials which can swell by absorbing water when the pH of the surrounding aqueous (water based) media changes.

• The effect is reversible with change in pH in the opposite direction to contract or collapse the material i.e. loses water.

Part 3c. TEMPERATURE-RESPONSIVE POLYMERS

• Temperature-responsive polymers are materials which undergo changes if the temperature changes.

• This is essentially a response to a cooling or heating stimulus.

Part 3d. SELF-HEALING MATERIALS

• Self-healing materials have the natural ability to repair damage themselves due to normal usage and so increase the material's useful lifetime

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INDEX of SMART MATERIALS PAGES

PART 1 CHROMOGENIC MATERIALS - Thermochromic, Photochromic & Electrochromic Materials

PART 2 SHAPE MEMORY ALLOYS e.g. Nitinol & Magnetic Shape Memory Alloys

PART 3 SHAPE MEMORY POLYMERS, pH and temperature sensitive-responsive polymers, self-healing materials

Part 4 LYCRA-SPANDEX

PART 5 High performance polymers like KEVLAR

PART 6 GORETEX, THINSULATE and TEFLON-PTFE

PART 7 PIEZOELECTRIC EFFECT (PIEZOELECTRIC MATERIALS) and PHOTOMECHANICAL MATERIALS

PART 8 CARBON FIBRES

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