NOTES

• Smart materials:

  • Smart materials react to an external stimulus by changing their characteristics and/or properties
• Self-healing polymer:

  • Self-healing polymers react to stress fractures by releasing a resin into the new crack
  • Microcapsules of liquid resin are ruptured to bond the polymer back together again
• Self-healing concrete:

  • Designed to avoid stress cracks filling with water
  • Cracks enlarge over time and water can cause the steel reinforcements to rust and weaken the structure
  • Self-healing concrete has spheres of bacteria added to the mixture which contain their own food
  • When a crack forms and water seeps in, the bacteria start to feed, producing calcium carbonate which fills the crack
• Thermochromic pigments:

  • Hot and cold temperatures trigger a change of colour in special thermochromic dyes
  • Applications include:
  • Fever scan strips used on infants
  • Room thermometers
  • Children's cutlery and crockery
  • Novelty goods and colour changing clothing
  • Some pigments have a permanent change
• Photochromic particles:

  • Ultraviolet light reacts with photosensitive silver halide particles within the lenses
  • This reaction is commonly seen in prescription sunglass lenses that darken in bright sunlight and return to clear indoors
  • The reaction can take up to two minutes to complete
  • Over time the particles can lose their ability to revert to clear
• Photochromic pigments:

  • UV light stimulates particles in a special pigment
  • The effect only lasts as long as strong UV light is present
  • These pigments are mainly used for novelty goods and colour changing paints
• Shape memory alloy (SMA):

  • Nitinol is an SMA of nickel and titanium
  • Nitinol needs to be ‘set’ into a shape which requires a high temperature of around 540°C
  • Once set, the alloy can be deformed into a different shape
  • Heat or electricity is used to trigger a response in its shape
  • When reheated to around 70°C it will go back to its pre-set shape
• Quantum Tunnelling Composite:

  • QTC is a polymer that contains billions of metal particles that don’t actually touch each other
  • It is an unusual material being both an insulator and a semi-conductor
  • When pressure is applied the polymer becomes a conductor allowing an electrical signal to flow
• Piezoelectric material:

  • Piezoelectric material works in two ways:
  • Subject it to movement or stress and it produces electricity
  • Attach an electrical signal to it and it moves
• Piezo transducer:

  • Using a thin layer of piezoelectric material, small transducers vibrate when an electrical signal is sent through the contacts
  • These are used in mobile phones and other small electronic devices and toys
  • When tapped or spoken into they produce a small electrical charge that can be amplified to create sound or trigger a response in a circuit
• Acids and alkalis:

  • PH levels can be detected using litmus paper
  • It uses compounds found in different varieties of lichen
  • Different colours and shades appear depending on the PH
  • Common uses include: Garden soil testing / pool water testing / skincare products – (dermatological testing)