Engineering materials (smart materials)
There is no clear-cut definition of a smart material. The name is commonly applied to materials or components that exhibit some kind of useful response to an external change such as light, heat or pressure. Some of these materials have been discovered eg quartz a naturally occurring piezoelectric material (this produces an electrical signal when squeezed) while others have been manufactured for a particular purpose eg hydrogels (developed by NASA for absorbing body fluids while astronauts were wearing space suits).
The term smart is often applied to complete products to emphasise that they seem to have a ‘mind of the own’ although some products contain components that are ‘intelligent’ or ‘smart’. Many smart materials have originated in the 21st Century but some have a longer history eg the use of bi-metallic strips from the 17th Century and porous ceramics used in the ancient world.
Developments in scientific knowledge have resulted in the design and manufacture of a wide range of metals, plastics and composites with specific and desired properties.
This list provides some suggested activities that can be used with students to demonstrate the properties and applications of some of the most common smart materials.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to health and safety and that they carry an appropriate risk assessment. Further information is provided in our health and safety guidance
Shape Memory Alloys
This Video clip can be used to introduce the topic of Shape Memory Alloys.
When a smart wire is heated it contracts. When it is cooled it remains the same length. If a force is now applied to it, it stretches back to its original length.This is because the smart wire is made of an alloy of nickel and titanium in a 1:1 ratio. The alloy can exist in three different forms, each with a different arrangement of the nickel and titanium atoms. Initially, smart wire is in the Deformed Martensite form. When it is heated, the atoms rearrange into the Austenite form, and this leads to a contraction in its length. The Austenite form is the ‘remembered’ form of the alloy. When the Austenite cools down, the alloy changes to Twinned Martensite. The Twinned Martensite form is the same size and shape as the Austenite on a macroscopic scale, so that there is no visible change in the wire when it cools. If a force is now applied to the wire, it stretches as it changes from the Twinned Martensite to the Deformed Martensite form. The form that is most stable depends on the conditions.
A knowledge of the structure of metals and their alloys will be required to fully explain these properties.
The Catalyst article 'Using Shape Memory Alloys can be used to introduce how they can be used:
http://www.nationalstemcentre.org.uk/elibrary/resource/2627/using-shape-memory-alloys
This article describes the use of smart materials to help people with disabilities
Metals and Smart Alloys
This booklet produced by the Science Enhancement Programme (SEP) is mainly aimed at Key Stage 4 but can be used as an introduction to Memory Shape Alloys. The following two activities can be used to model the way in which the latest ‘smart’ or ‘shape memory’ alloys work and introduces some of their applications.
Activity B1 page 36 shows a good way of introducing the principles of the shape memory effect using a model of a robotic arm. The model uses two pieces of thin smart wire connected to a lever on either side of a pivot. When a battery is connected to one of the smart wires, the wire contracts (by about 5%) and the lever moves. If the battery is disconnected, and current is now passed through the other wire, the lever moves back in the opposite direction. When a smart wire is used like this it is also called muscle wire.
Activity B5 page 41 demonstrates how the principles of training a smart alloy can be explored quite simply using a piece of memory wire. Training a sample of a smart alloy generally involves a complex process of treatment over a number of cycles in which it is deformed, heated and cooled.
This can be followed up by using the activity 'Which Material?2:
http://www.nationalstemcentre.org.uk/elibrary/resource/8874/which-material-2
In this activity students investigate the properties of smart springs and see how they might be used as muscles in a robotic arm.
Some other medical applications of shape memory alloys can be found at:
QTC - Making the Most of a Novel Material
This Catalyst article can be used to introduce Quantum Tunnelling as a composite designed by accident.
Its resistance decreases dramatically under pressure. In this article, David Bloor of Durham University describes how QTC was discovered and how his team set about exploring this strange new material.
QTC: A Remarkable New Material to Control Electricity
This booklet provides a comprehensive overview of the discovery, properties and applications for QTC with suggestions for teachers on how to introduce the ideas in the classroom, plus student activity sheets and notes for teachers and technicians.
QTC (Quantum Tunnelling Composite) was invented (or discovered) by David Lussey in 1997. It was an ‘accidental’ discovery as he was trying to develop an adhesive that would conduct electricity.
QTC consists of tiny nickel particles embedded in a rubbery polymer material. When QTC is deformed in some way - by squeezing, stretching or twisting - the nickel particles get closer to each other and the material becomes a conductor. The more it is deformed, the closer the particles get and the better the material is at conducting electricity
This unique property opens up a vast range of domestic and industrial applications - finger sensors for robots to give them touch-sensitivity, a musical keyboard that you can fold up, switches with no moving parts, clothing with electrical controls made of fabric, and amazingly sensitive ‘electronic noses’ are just a few.
Thermochromic Pigment
This video clip can be used to introduce Thermochromic materials.
Thermochromic materials are typically microencapsulated, with the microcapsules having a diameter typically between 3 to 5 µm, which is significantly larger than traditional pigment particles. The active mixture of compounds often contains leuco dyes in a low-melting point solvent that is a solid at room temperature. These dyes have two forms, one coloured and one colourless. When the solvent is solid, the dye is in its coloured form. When the temperature is increased and the solvent melts, the dye changes to its colourless form. By mixing a microencapsulated thermochromic pigment with a thermoplastic polymer, versatile products can be made that change colour when the temperature changes, for example, a bath toy that changes colour to warn when the water is too hot.
Thermocolour film changes colour from black through red, green and to blue as the temperature increases. Students can use this film to investigate the thermal conductivity of different materials. Initially, students could compare the effect of placing a beaker of hot water on thermocolour film which has been placed on a metal lid with film which has been placed on a plastic lid. They should find that a coloured halo spreads out rapidly on the metal lid, but slowly on the plastic lid.
Targeted drug delivery is an example of an application of microencapsulation.
Smart Grease
'Silly putty' can be used as an introduction to Smart Grease. The following video clip demonstrates the properties of Silly putty:
http://www.nationalstemcentre.org.uk/elibrary/resource/7284/putty
Silly putty is a viscoelastic polymer or dilatent compound which has engineering applications like smart grease.
This class of material has the remarkable property that it usually behaves as a soft mouldable plastic (like chewing gum), but instantly becomes a rubber if impacted.
Smart putty is made from a silicone polymer. A silicone is a polymer with a backbone of alternating silicon and oxygen atoms with organic functional groups attached. The most widely used silicone is polydimethylsiloxane, which has the formula [-Si(CH3 ) 2 O-]n . In smart putty, there are silicone molecules that have hydroxyl groups, -OH, and these result in cross-linking between the silicone polymer molecules. Smart putty is viscoelastic, and at low temperatures behaves like an elastic solid, but at high temperatures it will flow like a viscous liquid. The cross-linking between the silicone chains allows the material to stretch when pulled slowly, because the cross-links can re-form with other parts of the chain. However, the material breaks when pulled quickly as the cross-links do not have time to form in new positions.
Students can investigate:
Symbol">·
The behaviour of smart putty under different conditions and compare this behaviour to that of a solid or liquid.
Symbol">·
They can compare the effects of stretching the smart putty slowly or quickly.
Symbol">·
The drop height and subsequent bounce height of a small sphere of smart putty. This behaviour is similar to an elastic solid.