Smart Materials (AQA GCSE Design & Technology): Revision Note

Changing material properties through external stimuli

What is a smart material?

• A smart material is one that changes its properties in response to an external stimulus

• External stimuli include:

  • Stress — force, pressure or stretching

  • Temperature — changes in heat (both hot and cold)

  • Moisture — water or humidity in the air

  • pH — acidic or alkaline conditions

• A smart material will react to one of these stimuli and change, giving products additional functionality

What is a shape memory alloy (SMA)?

• A shape memory alloy (SMA) is typically a metal which returns to its original shape (if deformed) when heated

• The external stimulus of a shape memory alloy is temperature

• Shape memory alloys can be bent, stretched or deformed and then heated to return to their desired shape

• An example is in glasses frames (spectacles), where accidentally bent frames can be returned to their original shape by placing them in hot water

• Shape memory alloys help make products longer lasting and durable, or can replace the need for a motor or mechanism

• A high-end example is in sports cars, where air flow panels on the body open and close automatically if the engine starts to overheat during fast driving

What is thermochromic pigment?

• A thermochromic pigment is a pigment (typically of paint) which changes colour when it gets hotter or colder

• The external stimulus of thermochromic pigment is temperature

• Thermochromic pigment can be applied to the outside of products or embedded into them

• A common example is in products for young children and babies, where a parent may want to check the temperature of bath water (using a thermochromic bath toy) or food (using a thermochromic spoon or bowl)

• Another example is on food packaging, where a significant temperature change that could spoil the food inside is communicated using colour-changing labelling

What are photochromic pigments?

• Photochromic pigments are pigments which change colour in reaction to exposure to UV light

• The external stimulus of photochromic pigment is UV

• Photochromic pigment is ideal for products where a user would like to know if they are being exposed to too much UV through sunlight

• Photochromic pigment is commonly used in sun-reactive clothing or sunglasses and safety labels

• Another common use is in glasses which function as both reading glasses and sunglasses, changing their appearance to dark when the lens is exposed to high levels of UV