Smart materials

Smart materials

Smart materials react to an external stimulus by changing their characteristics and/or properties

Self-healing polymer

Self-healing polymers react to stress fractures by releasing a resin into the new crack
•Microcapsules of liquid resin are ruptured to bond the polymer back together again

Self-healing concrete

Designed to avoid stress cracks filling with water
•Cracks enlarge over time and water can cause the steel reinforcements to rust and weaken the structure
•Self-healing concrete has spheres of bacteria added to the mixture which contain their own food
•When a crack forms and water seeps in, the bacteria start to feed, producing calcium carbonate which fills the crack

Thermochromic pigments

Hot and cold temperatures trigger a change of colour in special thermochromic dyes
•Applications include:
•Fever scan strips used on infants
•Room thermometers
•Children's cutlery and crockery
•Novelty goods and colour changing clothing
•Some pigments have a permanent change

Photochromic particles

Ultraviolet light reacts with photosensitive silver halide particles within the lenses
•This reaction is commonly seen in prescription sunglass lenses that darken in bright sunlight and return to clear indoors
•The reaction can take up to two minutes to complete
•Over time the particles can lose their ability to revert to clear

Photochromic pigments

UV light stimulates particles in a
special pigment
•The effect only lasts as long as
strong UV light is present
•These pigments are mainly used
for novelty goods and colour
changing paints

Shape memory alloy (SMA)

Nitinol is an SMA of nickel and titanium
•Nitinol needs to be 'set' into a shape which
requires a high temperature of around 540°C
•Once set, the alloy can be
deformed into a different shape
•Heat or electricity is used to
trigger a response in its shape
•When reheated to around 70°C it
will go back to its pre-set shape

Quantum Tunnelling Composite

QTC is a polymer that contains billions of metal particles that don't actually touch each other
•It is an unusual material being both an insulator and
a semi-conductor
•When pressure is applied the polymer becomes a conductor allowing an electrical signal to flow

Piezoelectric material

Piezoelectric material works in two ways:
•Subject it to movement or stress and it produces electricity
•Attach an electrical signal to it and it moves

Piezo transducer

Using a thin layer of piezoelectric material, small transducers vibrate when an electrical signal is sent through the contacts
•These are used in mobile phones and other small electronic devices and toys
•When tapped or spoken into they produce a small electrical charge that can be amplified to create sound or trigger a response in a circuit

Acid or alkali?

PH levels can be detected using litmus paper
•It uses compounds found in different varieties of lichen
•Different colours and shades appear depending on the PH
•Common uses include: Garden soil testing / pool water testing / skincare products - (dermatological testing)