Rugby School Thailand Design & Technology Senior School

8.7 Smart materials

Syllabus content

• The working properties, common uses and environmental impact of the following:

– pigments ○ phosphorescent ○ photochromic ○ thermochromic

– shape memory alloys (SMA) ○ nickel ○ titanium

– hydrogels

– shape memory polymers.

A smart material is a material that responds, in a reversable way, to a change in environmental conditions.

Smart pigment

Pigment is what gives a material its colour, it’s in nature and even in our skin; it is what makes something a particular colour or hue.

By replacing traditional pigments with smart pigments we can affect the colour of a materials by subjecting them to heat or light.

Smart pigments have a variety of practical uses and can be incorporated into fabrics and polymers in the same way that you might mix in a paint or dye to colour a material while it is being formed.

Phosphorescent pigment

Phosphorescent materials have the unique ability to absorb light and then use that light to provide low level illumination in dark or low light conditions. The pigment can be used in paint or polymers, and products using this pigment are commonly referred to as a ‘glow in the dark’.

Photochromic pigment

‘Photo’ relates to light and ‘chroma’ to colour. Therefore Photochromic pigments change colour when exposed to sunlight. Common examples are paints and fabrics designed to change from white or clear to coloured when exposed to sunlight.

Thermochromic pigment

‘Thermo’ relates to heat and ‘chroma’ to colour. Therefore Thermochromic pigments change colour when exposed to heat. Common examples are baby spoons, kettles and thermometers.

Shape memory alloys (SMA's)

SMA’s are alloys that have a material memory. In other words they remember their original shape. Some have an elastic memory so when deformed, will bounce back into shape like the flexible spectacle frames. Others will remember their shape when heated and return to their ‘shaped’ position when they cool down. Perhaps the most common is Nitinol (Nickel Titanium) used for glasses and dental braces.

**Hydrogels

Smart hydrogels can change their hydrophilicity, swelling ability, physical properties, and molecules permeability, influenced by external stimuli such as pH, temperature, electrical and magnetic fields, light, and the biomolecules' concentration, thus resulting in the controlled release of the loaded drugs

***Smart fluids

Fluids no longer have to exhibit the properties we were once taught in science. A magnetorheological fluid is a fascinating smart fluid with the ability to switch back and forth from a liquid to a near-solid under the influence of a magnetic field. It is usually used for applications in braking. Magnetic oil adheres to metal and there are many more.

Van der Waals ferrofluid speaker - yanko design

**Shape memory polymers

Shape-Memory Polymers (SMPs) are considered a kind of smart material able to modify size, shapes, stiffness or strain in response to different external (heat, electric and magnetic field, water or light) stimuli including physiological ones such as pH, body temperature and ion concentration

Two frequently used SMPs are polylactic acid (PLA) and thermoplastic polyurethane (TPU), owing to their excellent shape memory properties, biodegradability, and biocompatibility.

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