Smart Materials (WJEC GCSE Chemistry: Combined Science)

• Smart materials are ones which can have their properties changed in a reversible way 
  • For example, a material might be able to have its shape changed, but can revert back to its original shape if the conditions are changed, such as being heated up 

Photochromic pigments 

• These materials change colour depending on the light intensity 
• These materials are used in photochromic lenses for glasses
  • These lenses will darken when exposed to UV light so can be used as sunglasses on sunny days but normal glasses when they are no longer in sunlight

Thermochromic pigments

• The term 'thermo' refers to heat and 'chroma' means colour 
• These materials therefore change colour as the temperature changes
• These materials are used in colour changing mugs and strip thermometers 

Image from Adobe

The mug changes colour at different temperatures

Polymer gels

• Polymer-gels are able to absorb up to 1000 times their own volume in water 
• The water molecules join weakly to the polymer chains causing the gel to swell 
• If the gel is placed into dry conditions, it will release the water slowly 
• Uses of these include nappies and granules which are added to soil to help plants retain water 

Shape-memory alloys

• Alloys are mixtures of metals
• They can revert to their original shape when heated
• They are also used in sporting equipment like helmets, and car bodies 
• Another use is in surgical plates for joining bone fractures: 
  • As the alloy is warmed by the body, it applies tension which allows for quicker healing

Shape-memory polymers

• This type of polymer can be bent out of their original shape but revert back when heated 
• These are used in car bumpers so that if a collision occurs it can be returned to its original shape 
• They are also used in helmets and gum-shields 

Diagram to show a shape-memory polymer

The heat will cause the polymer to revert back to its original shape