What are smart and modern materials and how do they respond to their surroundings?
Smart materials that change a property in response to a stimulus, and modern materials developed through new processing, with examples and uses.
A focused answer to AQA GCSE Engineering on smart materials that respond to a stimulus (shape memory alloys, thermochromic and photochromic pigments, piezoelectric materials) and modern materials such as graphene, with their properties and uses.
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What this dot point is asking
AQA wants you to explain what makes a material "smart", give examples with their stimulus and response, and recognise modern materials that exist because of new processing. You should match a smart or modern material to a sensible use and keep the smart-versus-modern distinction clear.
What makes a material smart
Common stimuli are temperature, light, electrical current, pressure and pH. The material does the sensing itself, so a smart material can replace a separate sensor, circuit and actuator with a single component. This is why smart materials are valued in engineering: they simplify a product by combining sensing and action in one material, often with no power supply, fewer parts to fail, and a faster or more reliable response than an electronic equivalent. The trade-off is that a smart material gives a fixed response built into the material, so it cannot easily be reprogrammed the way a microcontroller can; the designer chooses a smart material when the simplicity and self-acting behaviour outweigh the loss of flexibility.
Examples of smart materials
Modern materials
Modern materials exist because of new processing methods rather than a response to a stimulus. Graphene is a single layer of carbon atoms that is extremely strong, light and a good conductor of heat and electricity. Other examples include nanomaterials (engineered at the scale of atoms and molecules) and metal foams that are light but stiff. They are "modern" because the technology to make them is recent, not because they react to their surroundings.
Try this
Q1. Name the stimulus that a thermochromic pigment responds to. [1 mark]
- Cue. Temperature (heat).
Q2. Give one use of a piezoelectric material. [1 mark]
- Cue. A sensor, a gas lighter or igniter, or a microphone.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20183 marksExplain how a shape memory alloy is used in a thermostatic safety valve.Show worked answer →
A good answer links the stimulus to the change in property and the result.
A shape memory alloy (SMA) such as Nitinol returns to a remembered shape when it is heated above a set temperature. In a safety valve the SMA element is set so that, as the temperature rises past the trigger point, it changes shape.
This movement opens (or closes) the valve automatically without any electronics, then the alloy returns to its first shape when it cools so the valve resets. The response to heat is what makes it useful for automatic temperature control.
Markers reward the stimulus (heat), the change (returns to a remembered shape) and the useful result (the valve operates automatically).
AQA 20224 marksExplain the difference between a smart material and a modern material, using one example of each.Show worked answer →
A good answer defines each clearly and supports it with an example.
A smart material changes one of its properties in response to an external stimulus (heat, light, pressure, electricity), and the change is usually reversible. For example, a thermochromic pigment changes colour as its temperature rises and returns when it cools.
A modern material is one developed through new processing or technology that gives it outstanding properties, but it does not respond to a stimulus. For example, graphene (a single layer of carbon atoms) is extremely strong, light and conductive because of how it is made, not because it reacts to its surroundings.
Markers reward the stimulus-response definition of smart with a valid example, and the new-processing definition of modern with a valid example such as graphene.
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Sources & how we know this
- AQA GCSE Engineering (8852) specification — AQA (2017)