Smart materials

• material categories

  • traditional - materials that have been used for many centuries
  • modern - materials developed in the last century
  • smart - materials that change physical properties
• smart materials are modern materials but the definition of a smart material: are designed (synthetic) materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli - stress, temperature, moisture, pH, electric or magnetic fields

  when you do something to the material it physically changes but can also change back
• smart pigment can change the colour of a product/material due to external factors

  • thermochromic pigment - change when exposed to heat - baby spoons
  • photochromic pigment - change when exposed to sunlight - paints and fabrics
  • phosphorescent pigment - absorb light and then use light when in low light/dark conditions - paint or polymers (glow in the dark)
• shape memory alloys (SMAs) and shape memory polymers (SMPs)

  • materials where large deformation can be induced and recovered through temperature or stress changes
  • the deformation occurs due to martensitic phase change
• electroluminescent wires

  • same effect as neon but in a flexible wire
  • no gas, be powered by AA batteries and can last for hours
• piezoelectric materials

  • materials that produce a voltage when stress is applied
  • can apply in the reverse manner as voltage will produce stress within the sample
  • structures made from this material can bend, expand or contract when voltage is applied - speakers found in phones
• smart fluids

  • magnetorheological - has the ability to switch back and forth from a liquid to a near-solid under the influence of a magnetic field
  • usually used for breaking applications - magnetic oil
• smart textiles

  • materials can repel dirt or water and even refract light (invisibility cloak)
  • fabrics can incorporate other smart materials such as thermo/photochromic pigment
  • kevlar - can resist a bullet
• smart glass

  • glass can react to light, filtering out UV rays, tinting to reduce light, can become mirror like and can even be self-cleaning
  • solar cells coat glass and stay invisible while converting light into energy
  • sapphire and gorilla glass - scratch resistant
• smart grease

  • is a sticky viscous gel with shear characteristics
  • used to control movement, producing a dampened slowed down feeling
  • used on volume control knobs and soft close toilet seats
• chameleon nanoflakes

  • nano-sized silicon flakes covered with a titanium compound
  • possess light scattering properties if mixed with clear varnishes or polymers
  • commonly used to spray cars for a 'two-tone' effect
• quantum tunnelling composite (QTC)

  • small metallic particles combined with rubber
  • causes it to be an insulator and conductor due to the separate properties of the materials
  • can be sewn into fabrics to stop microswitches being exposed to water damage
• polymorph

  • a modern material that is sometimes considered a smart material
  • thermoplastic properties becoming malleable enough to shape in temperatures as low at 75 degrees
  • becomes soft in hot water and when cooled it becomes hard and rigid allowing it to be cut and drilled