Prepared by Dr Diane Aston, IOM3

Prepared by Dr Diane Aston, IOM3

The future is materials
MODULE THREE The future is materials Prepared by Dr Diane Aston, IOM3

The future is materials
The aim of this module is to introduce you to materials which have come to the fore in more recent years. These are the materials that will be helping to shape our future. Materials science and engineering is a fast moving field and by far the majority of the advances in the technology that we take for granted are driven by developments in materials. Functional materials are a relatively new group of materials that have some interesting and useful properties . Prepared by Dr Diane Aston, IOM3

Session 1 Smart materials
Prepared by Dr Diane Aston, IOM3

Aims and objectives The session aims to introduce you to the interesting collection of materials called Smart Materials. At the end of this session you should be able to: Give a broad definition of smart materials and cite an example of a type of smart material; Describe three types of colour changing polymer Describe three useful properties of shape memory alloys Give an example of where piezoelectric ceramics are used Give an example of where quantum tunnelling composite is used Prepared by Dr Diane Aston, IOM3

A quick recap... Everything around us is made from something and all of the materials we rely on come from natural resources found within the Earth’s crust. Materials are used everywhere and they are chosen for particular applications because of their specific useful properties. We split materials up into four main classes : metals, ceramics, polymers and composites. Within these groups we can describe materials as structural or functional. Prepared by Dr Diane Aston, IOM3

Structural & functional materials
Structural materials Functional materials Been using these materials for thousands of years. Chosen for their structural or mechanical properties: Strength Toughness Hardness Stiffness Used in the construction of everything around us. Started to make an impact on our technology in the last 50 years or so. Chosen for their functional properties: Optical properties Electrical properties Thermal properties Magnetic properties Smart behaviour Structural materials are the ones that you will see used in the majority of applications around you. For example many school chairs are made from a moulded polypropylene seat mounted on steel legs. These materials have been chosen because they have the right structural properties for the job, in other words they are strong enough to support the weight of a person sitting on them! Functional materials tend to be used primarily for some other property. The key property of the very pure silica glass fibres that carry high speed broadband and cable TV signals relate to its optical behaviour. The electrical behaviour of semiconducting materials is key to their applications in microchips and other devices. The thermal properties of materials are crucial in some applications, such as insulating materials on space vehicles. The magnetic properties of iron have allowed it to be used in many applications. By alloying with other materials (namely neodymium and boron) we can create supermagnets which have a very large field for their size. Smart materials come under the banner of functional materials because they are used for some other interesting behaviour that they have, aside from their structural properties. Prepared by Dr Diane Aston, IOM3

What are smart materials?
A special group of metallic, polymeric, ceramic and composite materials that exhibit unusual behaviour. They experience a change in one specific property with a change in a specific aspect of their surroundings. Some change colour, opacity, size/shape, electrical conductivity, viscosity, stiffness. Some change with a change in temperature, UV light level, presence of an electrical or magnetic field, strain rate, shear rate, applied pressure. Smart materials appear to be intelligent as they undergo a specific change in one particular property with a change in one specific aspect of their surrounding environment. Prepared by Dr Diane Aston, IOM3

Why are smart materials special?
Change is not controlled by external circuits or microchips. Change is inherent to the material. Change occurs because the structure of the material is changing. Atoms or molecules moving their position very slightly produce a change which is easy to see, measure or detect. The key thing with the change is that it is an inherent property of the material and in most instances the change is reversible (if only on a microscopic level). In order for the change to occur the atoms or molecules change their position or shape very slightly and this produces a change in colour or shape which is either clearly visible or easy to measure or detect. Prepared by Dr Diane Aston, IOM3

Smart metals The shape memory effect was first observed in a gold- cadmium alloy in 1932. In the 1960’s Nitinol was developed and despite there being other SMAs available it is still by far the most commonly used as it is by far the most versatile SMA. The memory temperature can be controlled by controlling the composition of the alloy and by changing how it is processed it can be designed to show one of three useful properties. Entirely by coincidence, Nitinol is biocompatible so it can safely be used alongside and inside the human body. Nitinol is made by mixing roughly equal numbers of nickel and titanium atoms together and was discovered by researchers at the Naval Ordnance Laboratories in the US in the 1959 and developed throughout the 1960s. By changing its composition very slightly the memory temperature can be finely controlled to be anywhere between about -100ºC and +100ºC. This makes it useful for application in many environments. By changing how the alloy is then processed to shape it can be trained to demonstrate one of three different useful properties. Other shape memory alloys include Fe-Mn-Si, Cu-Zn-Al and Cu-Al-Ni and although they are cheaper than Nitinol they are not as commonly used. The interesting behaviour of Nitinol arises from the fact that its crystal structure changes with temperature and deformation. These transformations are diffusionless, in other words the atoms within the crystals do not have sufficient time or energy to move very far; they remain bonded to the same neighbours, but in a slightly different position. As chemical bonds are not being broken the material does not suffer so readily from fatigue. Entirely by coincidence Nitinol is biocompatible, despite the high nickel content, so many of its more interesting applications relate to its use inside and alongside the human body. Prepared by Dr Diane Aston, IOM3

Superelastic behaviour
Very flexible materials, can be bent without suffering permanent deformation. Used in flexible spectacle frames, mobile phone aerials and under-wired bras. Useful in surgical tools which need to be kink- resistant. The superelastic behaviour of SMAs is often described as pseudoelasticity. If a piece of superelastic wire was trained to remember to be straight, provided huge strains are not introduced (you can’t tie it in a knot!) you can bend it and it will return to its ‘memory’ shape when the load is removed. It can go through this shape change and then recovery millions of times at small strains. In this instance the metal is in its austenite phase at room temperature. The introduction of strain causes the structure to transform to martensite which can accommodate the shape change. When the load is removed the martensite reverts to the more stable austenite phase and the original shape returns. This material has been used for many years to make bendy spectacle frames and it was used for making mobile phone aerials (remember when they had them!). Superelastic Nitinol can be used for making dental braces that slowly pull the wearers teeth back to shape without the need to keep having it tightened by the dentist. It can also be used for reinforcing stents (like the one shown in the photo) and for making kink resistant surgical tools that can be used to follow the contours of blood vessels during keyhole surgery. Prepared by Dr Diane Aston, IOM3

One way temperature memory
Remembers a memory shape above the memory temperature . Can be bent to shape during use and then reset by heating. Trained by heating and then quenching. Can go through thousands of cycles. In one-way shape memory metal the material undergoes a transformation from austenite to martensite as it is cooled from high temperature. This change in structure does not result in a macroscopic change in shape. The martensite is relatively soft and can easily be deformed. During the deformation process defects called twins are introduced into the structure which allow a change in shape without breaking bonds. When this deformed martensite is heated back through the memory temperature the structure reverts to the more stable austenite phase and as it does so it reverts to its memory shape. To train a one-way behaviour the metal must first be formed to its desired memory shape and then clamped while it is heated to high temperature. On quenching the memory shape is fixed and it can then go through the cycle of being deformed and heated an almost infinite number of times. The photograph shows a smart bone plate which has been designed to help the body mend itself faster. The surgeon received the plate in the top shape. This is the deformed condition (the structure is deformed martensite). They screw the two holes at each end of the plate to either end of the broken bone and then activate the memory by warming the plate to body temperature with warm saline solution. Upon heating the plate reverts to its high temperature austenite phase and changes shape. It can be seen in the photo that the bottom plate (the memory shape) is slightly shorter so it keeps the two ends of the bone in close contact and encourages more rapid healing. Couplings made from SMA are used to join the fuel lines on aircraft as they can be made virtually leak-proof. Prepared by Dr Diane Aston, IOM3

Two way temperature memory
The material ‘remembers’ different structures above and below the memory temperature. As it is heated or cooled it changes from one structure to the other. Change in structure generates a force, so can be used as a switch in a temperature controlled circuit. In this instance the alloy ‘remembers’ one structure and one shape below its memory temperature and another structure and shape above it. As it is heated and cooled through this temperature it will change shape between the two states. The wire in the photo has been formed into a coil (it is not a spring; deforming it in either condition can make it forget!). At room temperature it is about 1cm long and dropping it in boiling water results in the coil opening out and almost doubling in length. When it is removed from the water it reverts to its low temperature tightly coiled state. As it changes shape a force is produced and this can be used to open or close a switch in a temperature controlled circuit, such as the one that switches a boiling kettle off or the one in your central heating thermostat. Two-way shape memory metal wire can be trained to change shape when it is heated simply by passing an electrical current through it. This ability lends itself to some interesting applications as artificial muscles. If two wires are connected either side of a joint changing the length of one of them will cause the joint to bend or straighten. Prepared by Dr Diane Aston, IOM3

Smart polymers A number of different types of smart polymers which exhibit useful behaviour Thermochromic materials Photochromic polymers Electrochromic polymers Shape memory polymers Strain and shear rate sensitive polymers Prepared by Dr Diane Aston, IOM3

Thermochromic polymers
Appear to change colour at a given temperature. Based on polymers called leucodyes or liquid crystals. Change occurs because molecules are changing position. Available as pigments, paints and inks and used in many everyday applications Thermochromic polymers appear to change shape at a given temperature (their memory temperature) and they are based on two systems – liquid crystals and leucodyes. In each case the smart material undergoes a change in structure at a particular temperature giving a change from coloured to transparent. In leucodyes the change happens over a temperature range of a few degrees but in liquid crystals just a degree or so. The leucodye systems tend to be cheaper but less accurate and these can be found as a marketing gimmick in many objects such as spoons, bath ducks, egg timers, the kettle in the photos, t-shirts and takeaway coffee-cup lids. The colour changing pigment is incorporated into another material to give the apparent colour change. The body of the kettle in the photo is made from pink polypropylene but before it has been formed to shape this has been mixed with a small amount of a thermochromic pigment which is blue at room temperature. When the water in the kettle starts to warm the structure of the thermochromic pigment changes and it changes from being coloured to transparent. Eventually as the water is boiling the steam warms the whole of the kettle body causing it to become pink all over. As the kettle cools back to below the memory temperature of the polymer the pigment will revert to its low temperature blue-coloured state. The change from coloured to transparent has a limited number of cycles and many thermochromic materials are affected by exposure to UV light. Prepared by Dr Diane Aston, IOM3

Photochromic polymers
Appear to change colour with a change in the level of UV light. Used for coatings on spectacle lenses. Can also get photochromic paints and pigments. Photochromic materials have been around for many years and the most well known use is as a coating on spectacles so that they change into sunglasses on a bright day. In this case the structure of the photochromic coating is such that at low levels of UV it is colourless and transparent. At higher levels of UV the structure of the coating changes and it becomes tinted. As the process is reversible when you go back inside to a lower level of UV the coating reverts to its low UV state and becomes colourless again. Prepared by Dr Diane Aston, IOM3

Electrochromic polymers
Liquid crystal-based materials that change colour at the flick of a switch. The polymer molecules are charged so they align in the presence of an electrical field giving an opaque or tinted appearance. When the applied field disperses the molecules return to a random arrangement and the material becomes transparent. Electrochromic polymers tend to be based on liquid crystals, the molecules of which have a similar geometry to a pencil or matchstick – in other words they are relatively long in one dimension compared to the other two. These stick-shaped molecules can either be randomly arranged in which case the material appears transparent, or very ordered in which case the material appears coloured or opaque. In an electrochromic material these molecules are also charged. Without an electrical field present the molecules are randomly arranged and the coating appears colourless. When an electrical field is applied the charged particles align and form an ordered structure causing a colour change. These materials are still not that common but they can be used for interior and exterior windows in domestic or commercial buildings. Prepared by Dr Diane Aston, IOM3

Smart ceramics These are probably the oldest group of smart materials. Although the effects were first discovered in natural minerals such a quartz and this is still used in some instances, we now tend to use complex man-made minerals with a crystal structure designed to give the most exaggerated effect. Smart ceramics can be described as: Piezoelectric Pyroelectric – used in thermal imaging cameras Ferroelectric – used in RAM for computers Prepared by Dr Diane Aston, IOM3

Piezoelectric ceramics
First discovered by the Curie brothers in 1880 in quartz. Now lead zirconate titanate (PZT) most commonly used. They generate an electrical field when pressure is applied to change their shape. They change shape when an electrical current is applied. Found a wide variety of uses: Microphones and guitar pick ups Car air-bag actuators Linear motors Damping systems, e.g. in skis Flat panel speakers Energy harvesting Piezoelectric materials can be used either as a sensor to detect something happening (in which case a change in shape is used to generate an electrical signal) or an actuator to cause something to happen (in which case a current is passed through the material to change its shape). Small quantities of these materials tend to be incorporated into larger smart systems and these can be used in many areas. In a guitar pick-up or microphone the crystal changes shape with the vibration in the air. This is converted into an electrical signal and sent to the amplifier. In a car air-bag actuator the crystal changes shape on impact and this triggers the air-bag to go off. The crystals will go through many cycles of changing shape very precisely allowing them to be incorporated into tiny motors designed to move something over a small distance. The autofocus function on the digital camera in your mobile phone is likely to be controlled by a piezoelectric linear motor. Separate piezoelectric crystals can be used as sensors and actuators in systems designed to detect and damp out unwanted vibrations. Small piezoelectric transducers can be used to turn any flat, solid surface into a speaker. A current is passed through the crystal in the transducer to make it vibrate. This sets up vibration in the air that your ears pick up as music. In order to amplify the sound the transducer can be placed on a solid surface and that will vibrate too. Manufacturers of electronic devices such as tablets, laptops and mobile phones are exploring the use of piezoelectric materials to turn the device screen into a speaker rather than using a traditional electromagnetic speaker. Prepared by Dr Diane Aston, IOM3

Smart Composites Quantum tunnelling composite (QTC) is made of a fine nickel powder dispersed in a polymer resin. Discovered in 1990s and now exclusively produced and licensed by Peratech, the company set up by the inventor, at their site in North Yorkshire. The material is now used in applications worldwide and has even been into space! This material was created as a happy accident as its inventor was trying to make a conducting glue! After some initial experimentation on his own and with staff at Durham University he set up Peratech to develop the material further and find uses for it. Prepared by Dr Diane Aston, IOM3

Useful properties of QTC
With no applied pressure it is a near perfect electrical insulator. If enough pressure applied it is a reasonable metallic conductor. Electrical resistance of varies with applied pressure in a predictable way. The current flows by electrons jumping between the sharp points on spiky metal particles. Materials that behave as insulators until pressure is applied have been around for many years, particularly those made by embedding carbon particles in a polymer matrix. In this case the carbon particles have to touch to conduct so there is a more defined line between conduction and insulation. In the case of QTC the metal particles do not actually have to be in contact with each other. The particles are very rough and covered in sharp points. These allow electrons to jump the gap between particles by a phenomenon known as quantum tunnelling. The closer the particles are to each other, the higher the probability of the electrons jumping and so the better the material conducts. There is predictable relationship between the conductivity of the materials and the amount of applied pressure. Prepared by Dr Diane Aston, IOM3

Applications of QTC Sports Fencing jacket touch senor Training shoes pressure analysis Functional textiles Consumer electronics Touch sensitive screens Mouse buttons and games controllers Wii board and dance mats Flexible piano keyboard and drums Flexible qwerty keyboard Medicine Blood pressure cuff tension check Respiration monitor Functional prosthetic limbs Industrial Variable speed controllers for tools Sensing for robotics QTC has found many uses where it is either used as a simple pressure controlled switch or a variable resistor controller. The switches are very reliable as they contain no moving parts and the material is now available as ink which can be screen printed on to surfaces. The applications of this material are described in great detail on the Peratech website where you can also read about how the material is being used in touch sensitive screens for devices such as smart phones and tablets. Prepared by Dr Diane Aston, IOM3

Smart fluids Not all smart materials are solid! Magneto-rheological fluids consist of fine iron particles suspended in a liquid such as glycerol or vegetable oil. In the a absence of a magnetic field the material behaves as a liquid. When a magnetic field is applied the particles in the materials align and the liquid becomes solid. Used in braking and damping systems. Prepared by Dr Diane Aston, IOM3

Session 1 Summary Smart materials are an interesting collection of metals, polymers and ceramics with some useful properties. Smart materials can act as sensors and actuators that can be incorporated into larger systems to add a degree of automation or functionality. New uses for smart materials are being found all the time and these developments are being led by materials specialists. Prepared by Dr Diane Aston, IOM3

Activity time! Investigating thermochromic polymers Investigating shape memory alloys Investigating QTC Prepared by Dr Diane Aston, IOM3

Session 1 activities Investigating thermochromic polymers Investigating shape memory alloys Investigating QTC Prepared by Dr Diane Aston, IOM3

Investigating thermochromic polymers
Artefacts containing thermochromic pigments such as colour changing baby feeding spoons, bath ducks and egg timers are relatively cheap and readily available. Thermochromic sheet and paints are available from Mindsetsonline. You could also have a go at some of the experiments in the SEP Publication Hot and Cold: exploring temperature changes with thermocolour film, available from the National STEM Centre eLibrary. If you do not have the facilities to carry out practical work you could get your students to research thermochromic polymers and come up with an idea for a new application. Prepared by Dr Diane Aston, IOM3

Investigating shape memory alloys
In order to be able to do any practical investigative work on these materials you will need some samples. The best place to get them (if you haven’t already) is Mindsetsonline who sell shape memory metal superelastic wire, one-way wire and springs and wire and two-way coils. A range of activities are available in the SEP publication Metals and Smart Alloys available from the National STEM Centre e-library. If you do not have the facilities to carry out practical work you could get your students to research SMAs and come up with an idea for a new application. Prepared by Dr Diane Aston, IOM3

Investigating QTC QTC samples are available to purchase at a very low cost from Mindsetsonline and you can get ideas of activities you can do with the material in the SEP publication QTC: A Remarkable New Material to Control Electricity available from the National STEM Centre elibrary. If you do not have the facilities to carry out practical work you could get your students to research QTC and come up with an idea for a new application. Prepared by Dr Diane Aston, IOM3

Session 1 useful links The Wikipedia articles on thermochromic, photochromic and electrochromic polymers, shape memory alloys, nitinol and piezoelectric ceramics contain some useful technical information. The National Physical Laboratory do a considerable amount of research on piezoelectric materials (and they also have some good general education resources!) The Peratech site contains a wealth of interesting and useful information on QTC. The National STEM Centre eLibrary contains many useful publications and ideas for activities relating to all types of smart materials. You need to register to use the site but it doesn’t cost anything to do this. Although you can buy some examples of smart materials over the counter, some are a bit trickier to source. The best supplier we have found is Mindsetsonline who sell most of the smart materials discussed in this module. The IOM3 Discovery Boxes also contain examples of all these smart materials, for more information on how to borrow a box contact Prepared by Dr Diane Aston, IOM3

Prepared by Dr Diane Aston, IOM3

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