Chapter 9 - Smart Materials

What is the core definition of a smart material?

A material with one or more properties that are dramatically altered by an external stimulus.

To be classed as a smart material, a material must exhibit a physical change in response to an external stimulus and then what must happen when the stimulus is removed?

It must return to its original form.

Name four types of properties in a smart material that can be affected by a stimulus.

Colour, shape, volume, and conductivity.

List four examples of external stimuli that can affect a smart material.

Changes in temperature, levels of light, moisture, and pressure.

What kind of material can be programmed to remember a specific shape?

Shape memory alloys (SMAs).

What happens to a shape memory alloy (SMA) when it is bent out of shape and then exposed to a given temperature?

It will return to its programmed shape.

Name three ways a shape memory alloy can be activated.

Changes in weather, body temperature, and electrical current.

What is a common example of a shape memory alloy, which is an alloy of nickel and titanium?

Nitinol.

Why are dental braces made of Nitinol wire considered a smart material application?

Body heat activates the wire, causing it to exert a constant force to pull teeth into the correct position.

What smart material is used as triggers for sprinklers in fire alarm systems?

Shape memory alloys (SMAs).

Name two brand names for shape memory alloys mentioned in the source.

Nitinol and Memoflex.

What smart material changes its colour or opacity with a change in temperature?

Thermochromic pigment.

The prefix 'thermo' in thermochromic relates to heat, while the root 'chroma' relates to what?

Colour.

How can thermochromic pigments be incorporated into other materials like polymers?

They can be mixed in as an additive, giving the host material the same colour-changing properties.

Name two common consumer products that use thermochromic pigments.

Colour-changing mugs and bath items for children.

What is another name for phosphorescent pigment?

Glow in the dark material.

What external stimulus do phosphorescent materials respond to?

Light (natural or artificial).

How do phosphorescent materials work?

They absorb energy from light sources and then emit that light in the dark.

Name three common uses for phosphorescent pigments.

Watch faces, toys, stickers, paints, and safety signs (e.g., fire exit signs).

Photochromic pigment changes colour or opacity in response to what specific external stimulus?

The level of ultraviolet (UV) light.

What is a well-known application of photochromic pigments?

Spectacle lenses that are clear indoors but darken like sunglasses in bright sunlight.

Besides spectacles, name two other applications for photochromic pigments.

Clothing and novelty items.

Electroluminescent wire is made from copper wire coated in what substance?

Phosphor.

What stimulus causes electroluminescent wire to glow?

An electrical current flowing through it.

Name two properties of electroluminescent wire that make it suitable for outdoor use.

It is flexible and waterproof.

List three applications for electroluminescent wire.

Lighting, clothing/costumes, and accessories for bicycles/vehicles.

What energy conversion do piezoelectric materials perform?

They convert mechanical energy into electrical energy, and vice versa.

What specific type of mechanical energy is converted to an electrical charge by piezoelectric materials?

Pressure or vibrations.

Name two applications where piezoelectricity is used to generate a result.

Creating a spark in lighters, tripping burglar alarms, or generating sound for fire alarms.

While all smart materials are modern materials, are all modern materials necessarily smart?

No, modern materials are not necessarily smart.

Unlike most metals that expand when heated, the SMA Nitinol _

contracts

What modern material is an insulating rubber containing tiny particles of metal?

Quantum-tunnelling composite (QTC).

Quantum-tunnelling composite (QTC) is an insulator when resting and a _ when pressure is applied.

conductor

How does Quantum-tunnelling composite (QTC) become a conductor?

When squashed, the tiny metal particles within the rubber meet and allow the flow of electric current.

What type of modern material has the ability to repair itself, extending product lifespan?

Self-healing materials.

Name two examples of self-healing materials.

Polymers that can heal knife cuts, metals that resist corrosion, or concrete that can heal when cracked.

What type of modern material can be formed by a magnetic field and is used in hydraulic suspension?

Ferrofluids.

How do ferrofluids allow car suspension to be hard or soft as needed?

The strength of the applied magnetic field can be varied to change the suspension's properties.

What is Polymorph?

A polymer that becomes malleable when heated to about 62°C and hardens when it cools.

Due to its ability to be reheated and reshaped, Polymorph is perfect for what two applications?

Modelling and creating ergonomic handles.

A material's reaction to an external stimulus is called its _

functional reaction

What is the primary reason SMAs are only commercially viable in high-cost applications?

They are expensive.

The property of thermochromic pigment may transform from opaque to _ or change colour.

transparent

The reaction of photochromic pigments to UV light is described as a _ reaction.

reversible

Why is Quantum-tunnelling composite (QTC) often used in outdoor applications instead of microswitches?

Water might otherwise damage tiny microswitches, whereas QTC is more robust.

What is an alloy?

A mixture of two or more elements, where at least one is a metal.

What is a polymer?

A large molecule formed from many identical smaller molecules known as monomers.