By the end of this unit you should have developed a knowledge and understanding of:

• what constitutes a smart material

• the difference between a modern and smart material

• why different types of smart or modern materials are suitable for different applications

• common smart and modern materials

• the benefits of using smart materials

• how modern materials are used in products

Materials - definitions

Smart Materials

Smart materials are modern materials but modern materials are not necessarily smart materials….confusing! 🤯

What this means is that modern materials are those that have been discovered or invented fairly recently in the history of man such as Titanium, Plywood etc.

For a material to be 'smart' it really needs to have certain properties. This is the definition of a smart material:

Smart materials are designed (synthetic) materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.

In simple terms, when you do something to the material it physically changes but can also change back.

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.

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.

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.

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’.

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.

Many years ago if you wanted bright signs you would have made them from Neon which is a gas which is encapsulated in a glass container and glows when ignited. Electroluminescent wire gives the same effect but in a flexible wire with no gas and can be powered by AA batteries and lasts for hours.

The Piezoelectric effect is achieved by applying an input to a quartz crystal causing a desired output to be seen. If it is put under strain, a small electrical charge is produced. They come in two forms: sensors such as those in airplanes to convert the vibrations in the wings into electricity or they can be actuators that change shape or form when an electrical signal is applied such as the tiny piezo speakers found in smartphones.

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.

Textiles are another area where great advances have been made. Kevlar is a modern fabric which can resist a bullet. Materials can repel dirt or water and there is even a fabric which refracts light; essentially an invisibility cloak. As well as having their own unique properties fabrics can incorporate other smart materials such as thermo/photochromic pigment etc.

Glass was once a very basic material used simply for glazing and drinking vessels. Nowadays it is a very advanced material allowing for touch sensitivity, images and video and even heat and electricity to be conducted. Sapphire and Gorilla Glass are scratch resistant and can even have oleophobic and hydrophobic coatings. Glass can also react to light, filtering out UV rays, tinting to reduce light, can become mirror like and can even be self cleaning. A recent development is organic solar cells which can coat glass yet remain invisible while converting light into energy.

Smart grease is a particularly sticky and viscous gel with almost magical shear characteristics. It is used to control movement, producing a dampened, slowed down feeling. For example, smart grease is used on volume control knobs and soft close toilet seats. It is also used in cases for glasses and has replaced the system of gears and springs once used to slow down drawer opening mechanisms on CD and DVD trays. 

It can also be used in prototype applications to improve performance or it can be used in novel applications such as wound-up motors to provide uniform speed and torque output.

This material consists of nano-size silicon flakes each covered with a Titanium compound. The flakes possess amazing light scattering properties if mixed with clear varnishes or polymers. They can have a variety of uses but are commonly used to spray cars for a ‘two-tone’ effect.

QTC is unique in being an insulator and a conductor. Small metallic particles are combined with rubber. In normal use the rubber stops the flow of electricity (insulates) but when pressed the metal particles compress making the material a conductor. This means traditional micro switches which were prone to water damage can now be replaced with QTC and can be sewn into fabrics.