Smart stuff: the text for the booklet accompanying the Royal Institution Christmas Lectures 2002.
SMART STUFF by Philip Ball – A booklet to accompany
The Royal Institution Christmas Lectures 2002
Delivered by Professor Tony Ryan, December 2002
Lecture 1: The Spider That Spun a Suspension Bridge
Imagine this: a team of engineers arrives to build a bridge across a gorge, but they have no lorries filled with materials. Instead, they eat a hearty breakfast and then begin to pull sticky cables out of their bottoms. Leaping from one side of the chasm to the other, they create a criss-crossing web of cables, each one stronger than steel. If they make a mistake, putting a cable in the wrong place, they simply eat it up and start again.
Because we are not spiders (and not Spiderman either), we’ll never be able to build bridges this way. But this is how a spider makes its web. It can’t dig up iron ore and turn it into steel cables. It has to work with materials made within its own body, put together from the atoms and molecules in the food it eats. Yet despite all our technological capability, we still can’t make a fibre that has all the good points of spider silk.
So scientists would like to know just how the spider does it. If we can unravel the secrets of spider silk, maybe that will teach us how to make new, synthetic materials that are just as good, combining tremendous strength with lightness. Silk is also biodegradable – it disintegrates slowly and harmlessly in the environment – and it is made from renewable raw materials, substances that can be grown again. Spider silk isn’t the only natural material that chemists and technologists would like to imitate. Bone is strong, tough and resilient: it can bend without breaking. The shells of some shellfish are as hard as rock, but not brittle: even thin sheets don’t snap easily. Wood is tough and lightweight. We can make synthetic materials that share some of these properties, but nature constantly seems to do it better. How?
Spinning a web
Many of nature’s materials are fibrous: they are made up of many thin fibres packed or bundled together, like the fibres in rope or netting. Think of hair (and silk, of course), and the stringy texture of meat, wood and plant stems. Fibres are easy for living organisms to make, because the molecules that they use as building blocks are themselves a kind of fibre: they are long chains of atoms, called polymers. You can always weave thick fibres from thinner ones.
The word ‘polymer’ means ‘many parts’. Typically, a polymer molecule is made by starting with small, simple molecules called monomers, each containing a handful of atoms, and linking one of them up to another – and then linking another to that one, and so on like the carriages in a freight train. These monomers might all be identical, as they are in common plastics like polythene (which is short for polyethylene), polystyrene and PVC (polyvinyl chloride) – long names for long molecules! Some natural polymers are like this too. Cellulose, the main polymer in plant fibres, consists of joined-up sugar molecules. Plant fibres from wood, cotton and hemp have been used for many centuries to make paper, textiles and rope. The first synthetic fibre (see Natural or synthetic?), called rayon, was a form of chemically processed cotton cellulose.
But silk is a different kind of natural polymer. It is a protein, whose monomer components are molecules called amino acids. The spider gets amino acids from its food – from eating creatures caught in its web – and uses them to build the molecules of a protein that it will then turn into strands of silk.
Most of our own soft tissues – skin, blood vessels, muscles, tendons and so on – are made from proteins too. There are just 20 different types of amino acid found in proteins, but by shuffling the order in which they appear along the molecular chains, all manner of different materials and properties can be produced: for example, proteins that are stiff, stretchy, transparent, waterproof or sticky.
In spider silk there are usually only half a dozen or so different kinds of amino acid. A spider ‘knows’ how to combine them to make polymer fibres that are astonishingly strong. We might not think of spiders’ webs as strong because we can brush them apart easily. But that’s because the fibres are so thin. If we made steel wire as thin as web silk (about 20 times thinner than one of your hairs), it would break more easily than silk.
Industrial threads
What might we do with fibres this strong? Human-made fibres are used to tether ocean-based oil-drilling platforms to the sea bed, holding them fast even in the most furious storm. Fibres trapped in a block of solid resin, like hair frozen in ice, can make ‘composite’ materials that are both stiff (they don’t bend easily) and tough (they don’t break easily). Fibre-glass is like this, and so is the carbon-fibre material used to make tennis rackets and racing cars. Fibre-composite materials are even used to make aircraft and spacecraft.
The first ever completely synthetic fibre, nylon, was a kind of very crude artificial silk. Whereas the building blocks of silk are natural amino acids, those of nylon are synthetic chemicals. But the chemical links that join these molecules are very similar to those in silk.
Nylon fibres are used for all sorts of things, from textiles to guitar strings. But nylon is nowhere near as strong as silk. In the 1960s, American chemists discovered how to make much stronger fibres from a class of synthetic polymers called aramids. Kevlar, an aramid fibre made by the Du Pont chemicals company, is about as strong as silk, and about as lightweight too. One of its many uses is in bullet-proof jackets and body armour.
Kevlar and silk are strong because of the way their molecular chains are arranged. Making strong fibres isn’t really about ensuring that the individual chains are strong. After all, these chains are very short – in Kevlar, 10,000 of them laid end to end would stretch for only about a millimetre. What really matters is how the chains are bundled together. If you’ve ever tried pulling apart cold spaghetti in the bottom of a pan, you’ll know how the strands get entangled and stuck together. Many polymers are like this. It’s hard to rip a sheet of polythene because the molecular chains are all tangled up. If you pull it hard enough, the plastic stretches as all the tangled chains get lined up with each other – we say that the chains become oriented.
In silk, however, the protein chains are only tangled up in some places. Elsewhere they are packed together side by side in an orderly pattern, rather like crimped hair. This orderliness is like the way atoms are packed in crystals: each spaced the same distance apart, like a troop of soldiers. So in these crimped regions, the silk is basically a crystal.
When a polymer forms a crystal, it can’t easily be stretched or broken if pulled in the direction that the chains are facing. So the key to making strong polymer fibres is to get the chains to crystallise so that they all point along the fibre. All polymers have some ‘crystalline’ regions, where the chains line up, but silk has more than most, and this gives it its strength. The molecular chains of Kevlar are oriented too: they are less floppy than most polymer chains, and so they line up quite easily. It doesn’t really much matter what a polymer’s chains are made from: so long as you can make the chains line up, you can make strong fibres from it.
Synthetic silk
That’s one of the secrets of silk’s success: it’s not so much what it’s made from, but how you make it (see The history of silk). More than 300 years ago, an English scientist named Robert Hooke proposed that silk might be imitated by letting glue get tacky and then pulling it out into a thread. This is pretty much what a spider does with silk itself. Inside the spider’s body are glands where silk protein is made. These proteins are dissolved in water, making a sticky liquid. But the spider draws this stuff out into a thread by squeezing it through a tube in its rear, called the spinneret, and pulling the soft mixture rapidly into a long fibre. It is this ‘spinning’ process that stretches out and aligns the protein chains. We don’t yet know all the secrets of how the spider spins its yarn. If we simply make a tacky solution of silk protein and try to draw it into threads as Hooke suggested, the resulting strands are never as strong as real silk.
Even so, scientists are hoping that it will one day be possible to make silk artificially – perhaps by building an artificial spinneret. To get the raw silk protein, one of the most promising ideas is to reprogramme the genes of bacteria so that they manufacture it.
Spiders ‘remember’ how to put silk together from amino acids because this information is stored in their genes. These silk genes can be copied and pasted into the DNA of bacteria (see DNA and genes), which then produce silk protein themselves.
Some people are uncomfortable with the idea of genetic modification of organisms. Is it better to breed silkworms for their silk, or to breed genetically modified bacteria? Other researchers are trying to insert silk genes into goat DNA, so that the goats make silk protein in their milk. There’s no reason to think this would harm the goats, but is it right to do it? What do you think?
[Box 1: position next to Spinning a web text]
Natural or synthetic?
If people call something ‘synthetic’ or ‘artificial’ today, they often mean it as an insult: it implies that the thing is bland, ‘manufactured’, or possibly harmful. In contrast, nature appears to make things ‘cleanly’ and without waste.
But it would be wrong to think that ‘synthetic’ means bad or toxic, and ‘natural’ means good or safe. After all, some of the most deadly poisons known are made by plants and animals. And sometimes it’s hard to distinguish the natural from the artificial. Some drugs, for instance, contain ‘synthetic’ molecules – ones made in chemical factories – that are identical to molecules extracted from living organisms. The very first plastics were a mixture of natural and synthetic: rubber and celluloid (the plastic used to make photographic movie film) were made by chemical processing of natural polymers.
Normally, if a material is called synthetic, this means it has been made from some raw material by industrial chemical treatment. For plastics, the raw material is usually petroleum oil. A natural material is one made by living organisms, like skin or wood.
[Box 2: position next to Synthetic silk text near beginning]
The history of silk
The secret of silk-making was jealously guarded for centuries in ancient China, where it was first discovered more than 3000 years ago. In Europe, silk textiles were expensive imported materials, carried from the Far East along the Silk Road between China and Istanbul (then called Constantinople) in Turkey. The Romans didn’t know how to breed silkworms until silkworm eggs were smuggled into Constantinople in the 6th century AD. Even then, silk-making in Europe didn’t take off until about 600 years later.
Turning cocoon silk into threads for weaving silk cloth is a very delicate process. The natural silk has to be carefully unwound from the cocoon, and the threads are so fine that they are almost invisible. It could take a whole day to collect a pound of silk. No wonder it cost so much.
Eventually machines were invented for reeling silk from the cocoons and spinning it into threads and textiles. But because silk was still slow to produce, it has always been a luxury. Its great strength, however, meant that it served some purposes that no other fibres could achieve until the invention of strong synthetics like Kevlar. It is used for making parachutes, and Chinese warriors of the 6th century AD used it as padding for armour. In the early part of the 20th century it was even used in bullet-proof clothing.
[Box 3: position next to Synthetic silk text near end]
DNA and genes
DNA is a natural polymer molecule, made up of four different types of monomer. The sequence of these monomers along the chain is a kind of code, containing the information needed to make protein molecules. Each different protein is encoded in a stretch of DNA called a gene. So DNA is a molecular library in which cells store all the blueprints for their proteins.
Lecture 2: The Trainer That Ran Over the World
Training shoes are made to be treated badly. By the time they wear out, an athlete’s shoes will probably have run the distance from London to Turkey and back. The pounding that they’ll have suffered during that time is equivalent to dropping three blue whales onto them. And they’ll have absorbed enough sweat to fill a bathtub to the brim.
So we shouldn’t be surprised that trainers don’t last forever; it’s amazing that they last even six months. But they are no ordinary shoe. They have been engineered as carefully as a car, and made from many different materials – all hand-picked for the job. After all, if all we wanted was a strong trainer we could make it out of steel – but that wouldn’t help a sprinter break the world record! Instead there are bouncy plastics, waterproof fabrics, panels that reflect light, perhaps Velcro fasteners, and sometimes even pressure-activated lights in the heel! And powerful glues stick the whole thing together.
How do we make materials with all these properties? And how do we stick them together to make a training shoe? And what has this got to do with motor racing and Jumbo jets?
Big stretch
The soles of your training shoes are made from a type of rubber. Natural rubber was used hundreds of years ago by the tribespeople of Central America. It oozes as a gummy liquid from rubber trees. The Central Americans knew how to make waterproof footwear from this gum by coating their shoes or feet with it and letting it dry – the world’s first Wellington boots.
Rubber is a polymer: a material made of long molecular chains. These chains are flexible, and they bunch up into disorderly tangles. If we pull on a piece of rubber, the chains are stretched out and the material gets longer. But it won’t stay that way: once we let go, the rubber snaps back again. This is because the crumpled chains are like springs. By straightening them out, we make the chains store energy; when they spring back, this energy gets released. Some of the energy is converted to heat: the rubber warms up.
Materials like this, which can be stretched to many times their original length and then snap back when you let go, are called elastomers (see Tough or what?). We often call them ‘elastics’, but technically speaking an elastic material is something rather different: it has much less springiness.
Raw rubber gum is, however, very soft – more like gooey putty than the rubber we are familiar with. That kind – the kind used for rubber bands and car tyres – has been stiffened by a chemical treatment called vulcanisation, invented in 1839. This causes the springy chains of rubber gum to become linked to one another, turning the tangle of chains into a stiffer web.
Until the 1930s, natural rubber was the only elastomer known. That’s when the Du Pont chemicals company in the USA began to sell the first ‘synthetic rubber’, a polymer called Neoprene. During the Second World War, the rubber plantations in Malaysia, where most British rubber came from, were cut off. Because rubber was desperately needed for military vehicle tyres and other equipment, synthetic rubber was manufactured in great quantities. Without it, Britain would have found it very hard to fight the war.
Today there are many kinds of synthetic rubber. One of the most successful was a polymer first made in 1956: a kind of polyurethane called spandex. This is widely used as a fibre for sportswear: in stretchy clothing for cyclists and runners, in swimsuits, and as elasticated bandages.
Once rubber is ‘vulcanised’, it can’t easily be turned into a liquid again. So there’s only one chance to mould it into a shape, and it isn’t easy to recycle. Many trainer soles are now made of a so-called thermoplastic rubber, a synthetic material that can be melted and remoulded. Most commercial thermoplastic rubbers are block copolymers: polymers whose chains are made up of shorter chains of different polymers, joined end to end.
If your training shoes give you a ‘spring in the heel’, this won’t be thanks to the rubber soles but to the foamy plastic material that gets squashed between the sole and your foot. This is usually made from a polymer puffed out into a foam by blowing a gas through it while it is still liquid. The cushion enables the shoe to withstand constant pounding: it is an excellent shock absorber. Without this protection, long-distance runners risk damaging their joints from the jarring as their feet hit the ground.
Get a grip
For long-distance running, endurance is the key, and so shoes that cushion against shocks are essential. For sprinters this is less important; what matters most of all is speed. Sprinters’ shoes are being constantly improved to make them lighter and to fit better, but what also matters is getting a good grip on the track.
Grip is important in other sports too. It lets climbers cling to the steepest rock face. The tyres of Formula 1 racing cars are so soft they feel tacky to the touch – this provides a good grip on the roadway as the cars whizz around bends. The tyres, made of a mixture of synthetic rubbers, might last for only a few laps before needing replacement. They offer just the right compromise between grip and speed: if the tyres were too sticky, they’d slow the cars down. Climbers, on the other hand, don’t really mind how slowly they move as long as their boots help them to grasp the rock. ‘Strong men’ who pull cars and lorries from ropes wear climbers’ boots to give them the best grip on the ground.
Why are some materials sticky? It would be better to ask why things don’t stick together all the time, because there is a force of attraction between just about all materials. In that case, why don’t we stick to our seats? The reason is that there are usually very few points where two surfaces come close enough to feel this attractive force – even if we squeeze them. Most surfaces aren’t smooth at all. Even a plane of glass or a sheet of polished metal, if you look at it closely under a microscope, is covered in scratches and pits, like a range of hills seen from the air. When we bring two surfaces like this together, they touch at only a few points where bumps stick out. This means that the attractive forces between the surfaces are actually very small.
Sticky materials, however, are soft. They can be pressed into all the tiny hills and valleys like putty, filling them up and creating lots of close contact. Such materials are typically polymers, like clingfilm and Blutack. These are called pressure adhesives: they stick when pressed onto a surface, but can be pulled off again.
All glued up
But some adhesives are permanent. About one-fiftieth of the weight of your training shoes consists of glues that stick the other materials together. There is about the same proportion of glue in a Jumbo jet.
You might not much like the idea of an aeroplane being glued together. But this can actually be safer than other ways of fixing parts to one another. When the world land speed record was broken in 1997 by Andy Green, driving a car called Thrust SSC at 763 miles per hour, all the rivets holding the vehicle’s panels together were shaken loose and only the glue stopped the car from falling apart.
Modern glues can be immensely strong. Epoxy resins and adhesives made from polymers such as polyurethane and acrylics hold components together in some spacecraft. In the age of superglue, we have got used to the idea that just about any two surfaces can be bonded strongly and permanently – sometimes unintentionally!
Most glues work in the same way as pressure adhesives: as liquids, they flow into all the nooks and crannies of a surface. But the bond can then be made to last by turning the glue to a solid. In most household glues this is done by dissolving the adhesive itself (some kind of polymer) in a solvent: once squeezed out of the tube, the solvent evaporates and the glue dries hard. Other glues are solidified by ‘curing’: by triggering chemical reactions that form crosslinks between the polymer chains. Epoxy resins are set this way – typically, the resin is mixed with a ‘hardener’, a curing agent that changes the liquid into a rock-hard solid.
One of the most revolutionary ‘adhesives’ used today isn’t a real glue at all. Many training shoes are fastened not by laces but by flaps of Velcro. This is a bit like a pressure adhesive that never wears out: you can pull it apart again and again.
Velcro is a sort of ‘physical glue’: the two surfaces get hooked together. One surface is a mass of little plastic hooks, and the other is a fuzzy tangle of fibres. The hooks get snagged in the fibres, but are flexible enough to be pulled out without breaking.
Velcro is an example of a biomimetic material: it copies a trick learnt from nature. Its inventor was a Swiss engineer named Georges de Mestral, who was an eager hill walker. One day he found that his socks and his dog’s fur were covered in little seed pods or burrs, which were coated with spines that ended in hooks. De Mestral made an artificial material that clung to fuzzy fabrics in the same way, using little nylon hooks. The US military has made a silent Velcro that doesn’t make a ripping sound when opened.
Velcro has an amazing grip. A five-inch patch sticks securely enough to bear the weight of a fully-grown person. And yet it is easy to unpeel such a patch by hand. Peeling a pressure adhesive apart is much easier than pulling the whole bonded areas apart at once. When you peel, all the force of your pull is concentrated along the line where the two surfaces separate, so only a very small fraction of the adhering surfaces is being ruptured at any moment. Sticky tape uses the same principle: peeling is the only way to get it off.
Velcro has an amazing grip. A five-inch patch sticks securely enough to bear the weight of a fully-grown person. And yet it is easy to unpeel such a patch by hand. Peeling a pressure adhesive apart is much easier than pulling the whole bonded areas apart at once. When you peel, all the force of your pull is concentrated along the line where the two surfaces separate, so only a very small fraction of the adhering surfaces is being ruptured at any moment. Sticky tape uses the same principle: peeling is the only way to get it off.
[Box 1: position next to Big stretch text]
Tough or what?
What’s stronger: rubber or glass? We can stand on a thick sheet of glass, while a sheet of rubber will just bend. But we can easily break the glass with a hammer, whereas you can hammer forever at a sheet of rubber.
We tend to use words like ‘strong’, ‘tough’ and ‘hard’ interchangeably, but they mean quite different things. The strength of a material is the amount of force needed to break it. When we talk about strength, we usually mean what is technically called tensile strength. This refers to how hard you have to pull on the material in order to snap it. Steel piano wire has a higher tensile strength than string, for example.
Toughness is a measure of how much energy is needed to break a material. Rubber isn’t all that strong, but it is ‘tough as old boots’, because it absorbs a lot of energy before breaking. Most metals are tough, but glass and porcelain aren’t: they are hard but brittle, and shatter easily.
Stiffness simply means how bendy a material is. If you make two identical rods from different materials, and hang the same weight from both of them, the stiffer material is the one that bends least. A stiff material needn’t be strong: biscuits are stiff. And low stiffness doesn’t imply weakness: nylon isn’t stiff, but it’s strong!
Lecture 3: The Phone That Shrank the Planet
You’re lucky. You’re living through an information revolution that may be as important as the invention of printing five hundred years ago. But this information doesn’t come in books: it is on Internet web pages, and you can read all of them (over a billion, and growing by several million each day) from your home – and some even from on top of a mountain.
Seven years ago, there were about 16 million people in the world who used computer communication networks – sending emails, roving the Internet. That’s about twice the population of London. By the start of last year, this number had grown to 400 million, and by 2005 it is predicted to reach one billion: about one in every six people in the world.
The growth of mobile phones is just as spectacular. Twenty years ago they didn’t exist. Now it is predicted that there will be more than a billion mobile-phone users in the world by 2003. Already 45 million people use mobile phones in the UK – almost three-quarters of the population.
Why have these changes happened? Have we become hungrier for information, and more eager to talk to each other? Not really. But the technologies that let us do these things have become much, much cheaper.
Thirty years ago computers filled entire rooms and took hours to do the simplest task. Ten years ago, some people carried mobile phones as big (and as heavy) as a carton of milk. Today you can fit a powerful computer in your briefcase, and a mobile in your pocket. Perhaps in 10 years’ time we’ll laugh at today’s ‘clunky’ devices as we carry our computers in wristwatches and our phones in ear-rings.
In other words, communication and information technologies have got cheaper and more available mainly because they’ve got smaller. And this is because new materials and new ways of making and shaping them have allowed the electronic components of these devices – the electrical circuits, the batteries, the screens and loudspeakers – to shrink. The information revolution has been driven by the right materials.
Chips with everything
Computers, phones, televisions and CD players are all electronic: they work by sending electrical signals down wires and shunting them between electronic components. Today’s computers are friendly – they speak to us, they show us nice pictures, they offer us help. But all this is the result of signals hurtling around electrical circuits carved into little square wafers of silicon, called microchips. There are several chips in your mobile phone, and they enable it to do things that once only a large computer could manage, like playing games.
Silicon conducts electricity, but not as well as the copper used in old-fashioned electrical wiring: it is a semiconductor (see What makes a semiconductor conduct?). Its electrical conductivity can be controlled by altering its chemical composition – by mixing small amounts of other substances, such as boron and phosphorus, in with the silicon. It is this control that lets electronic engineers make devices such as transistors out of silicon. They have special techniques for cutting up thin layers of silicon into slabs and channels too small for the eye to see, which are the components and wires of a chip’s circuitry. It’s rather like making sandwiches small enough for a tea party of fleas.
As these methods for making silicon circuits have got better, the circuits have shrunk. The wires can now be so narrow that five thousand side by side would measure a millimetre across. This means that more and more components can be crammed onto each chip. The devices that the chips control have got correspondingly smaller, lighter and smarter. There are about as many transistors on some of today’s chips as there are people in Britain!
How long can this continue? At the present rate, in about 15 years’ time electronic devices on chips will be almost as small as individual molecules. But can you make a wire or a transistor from a single molecule? Well, scientists have done that already. As long ago as the 1970s, some researchers were predicting a technology called molecular electronics, in which individual molecules are wired together in circuits. Over the past 10 years, that dream has started to come true. For example, tubular molecules called carbon nanotubes have been used to make transistors: one transistor for each molecule. But it is a very big step from making individual devices to wiring thousands or millions of them up into circuits as fast and reliable as those on today’s silicon chips. We don’t know yet if it will be possible to make computer circuits from molecules.
There is another option, however. We can forget about electronics entirely, and start transmitting and processing information using light. This is called photonics, because the smallest ‘particle’ of light is called a photon.
A lot of IT and telecommunications already uses light. When you speak on a ground-line telephone, the signal encoding your voice is sent hurtling at the speed of light along a fibre-optic cable – a kind of ‘light wire’. But at each end of the fibre-optic network the signal is converted between a string of light pulses and a stream of electrical pulses. This hybrid technology is called optoelectronics. It’s a cumbersome business – imagine trying to hold a conversation with your friend in which your words first have to be translated into French and then re-translated into English. Some engineers would like to do the whole thing in the same language: to use photonics for both sending and processing the information. Some even dream of light-based computers, which could be faster than electronic ones.
In optoelectronics the light source is usually an electrically powered laser. Scientists can now make lasers small enough that thousands will fit on a pinhead, so they match the scale of silicon chips. Each of them contains a material that converts electrical pulses directly into light. The colour of the laser light depends on what this material is. For telecommunication, the light signals are encoded in infrared light, which is invisible. Infrared lasers are typically made from a semiconducting material called gallium arsenide.
But information technologists would like lasers spanning a wide range of colours. If you use more colours, you can send more information (more phone calls, say) simultaneously down a fibre-optic line, just as you can broadcast many radio signals at once using different frequency bands. But it also turns out that you can focus a blue laser to a smaller spot than an infrared laser.
This could be important for CD and DVD technology. Here the information on a disk – it might be music, video, words – is read by a laser beam and converted to an electronic signal so that you can see or hear it. If you can write the information smaller, you can get more onto the disk. A single CD might then contain many hours of music, not just a single album. But to read this ‘smaller print’, you need a more finely focused laser. Blue lasers could enable you to do that.
Until the mid-1990s, there were no good blue-light lasers suitable for small-scale optoelectronic devices. Then Japanese scientists discovered how to make a material called gallium nitride emit blue light. They developed the first long-lasting blue-light semiconductor lasers.
Moving pictures
You may have noticed in the last few years that a new type of traffic light is appearing. Each light is made from dozens of tiny ‘bulbs’ which switch on and off instantly, whereas the older lights glow and dim more slowly. These new lights are made from light-emitting diodes (LEDs). Like semiconductor lasers, they convert electricity directly to light. LED traffic lights became possible only after gallium nitride became available, because this material could provide green light sources as well as blue.
Displaying information is a crucial part of information technology. LED display screens are now used for showing train and bus times, spelt out in glowing red dots. Full colour is possible too. Television screens produce colours by mixing tiny dots of red, blue and green light – and LED displays can produce colour this way too. But whereas televisions are cumbersome and fragile, LED displays are robust and flat.
If you go to Piccadilly Circus, you can see big LED billboards showing movie-type advertising on huge colour screens. Have you seen the movie Blade Runner, where a detective in the future lives in a city haunted by giant, floating advertising screens? It makes you wonder how much we will welcome these new possibilities.
But how about a TV that you can roll up like a piece of paper and slip into a briefcase? Scientists in Cambridge have found out how to make LEDs in a whole range of colours from plastics that conduct electricity and act like semiconductors. These materials are flexible and should eventually be cheap to produce. There are already prototypes – trial versions – of plastic LED screens, some small enough to fit on a wristwatch. And new flat display screens are also being developed from other materials, such as ‘electronic ink’ (see E-ink).
Crystals that flow
You may have noticed in the last few years that a new type of traffic light is appearing. Each light is made from dozens of tiny ‘bulbs’ which switch on and off instantly, whereas the older lights glow and dim more slowly. These new lights are made from light-emitting diodes (LEDs). Like semiconductor lasers, they convert electricity directly to light. LED traffic lights became possible only after gallium nitride became available, because this material could provide green light sources as well as blue.
The screen on your mobile phone uses a device called a liquid-crystal display (LCD). The screen is divided up into a grid of spots called pixels. Each pixel is like a door that can be opened or closed, letting light through or blocking it off.
The door is made from a peculiar material called a liquid crystal. It sounds like a contradiction: aren’t crystals hard and solid, whereas liquids flow? But to scientists, a crystal is defined slightly differently. It is a material whose parts are lined up regularly, like soldiers standing in ranks. In a crystal like diamond, all the atoms are stacked in an orderly way, as if they are oranges on a greengrocer’s stall.
The molecules of a liquid are free to move around – this is why liquids flow. But in most liquid crystals the molecules are shaped like rods: long and thin. Like logs floating on a river, they tend to line up with each other, even while they keep moving. This means that the molecules in liquid crystals have orientational order – they point roughly in the same direction – but positional disorder – they aren’t necessarily spaced an even distance apart.
In an LCD pixel, light can get through only if the molecules all point in a certain direction. This direction can be switched electronically, turning the cell light or dark.
Liquid crystals have been known since the 1880s, but it wasn’t until the late 1960s that scientists found anything useful to do with them. That was when the first LCDs were invented. Today LCDs are a multi-billion dollar industry. And liquid crystals have other uses too. One kind changes colour at different temperatures, and is used in cheap and shatterproof thermometers.
Full power ahead
Mobile phones are only mobile because you don’t have to plug them into the mains electricity supply: they have their own batteries. It’s only in the past decade or so that batteries have become small, powerful and long-lasting enough to be used in portable devices like this.
An Italian scientist called Alessandro Volta (after whom the electrical volt is named) found in 1800 that a current would flow down a wire between a zinc and a silver disk when they were laid one on top of the other, connected by paper soaked in salty water. This was the first battery.
Batteries don’t provide power for ever: eventually they run down, unless they can be recharged. Not all batteries can be recharged. Car batteries are rechargeable, but they are big and heavy, with electrodes containing lead. Mobile phones and laptop computers usually use rechargeable lithium batteries. The earliest lithium batteries were developed in the 1980s, but they had a tendency to burst into flames, which is not really what you want a mobile phone to do. A new, safe and reliable form of lithium battery was first sold by Sony in 1991. The improvement was largely a matter of finding better materials for the battery components. Scientists are still searching for new materials to make lithium batteries even more powerful and durable. Who knows – perhaps one day you may never have to charge up your mobile for its (or your) entire lifetime.
[Box 1: position next to Chips with everything after It’s logical box]
What makes a semiconductor conduct?
Metals conduct electricity: that’s why electrical cables are made from copper wire. Some materials – many plastics, for instance – don’t conduct electricity: they are insulators. Because electrical cables are coated with plastic, we can hold them without getting electrocuted. Semiconductors sit somewhere in between: they do conduct electricity, but not as well as metals. If we think of a flow of electricity as like a flow of traffic, then conductors like metals are similar to a road filled lane to lane with heavy, swift-moving traffic, semiconductors are like a road with only one or two cars on it, and insulators are like a road blocked off by road works
In this picture the cars represent electrons: electrically charged particles that every atom contains. An electrical current corresponds to a flow of electrons. In electronic devices made from the semiconductor silicon, the ‘traffic’ is directed by electrical signals from other devices. This enables components like transistors to ‘talk’ to each other.
[Box 2: position next to Moving pictures]
E-Ink
In Steven Spielberg’s film Minority Report, people read newspapers on which the words are constantly changing to update the news. This isn’t science fiction – something like it exists already, called electronic ink (e-ink).
One version of e-ink consists of tiny round capsules, about the size of pollen grains, scattered over the surface of the ‘paper’. The capsules contain black and white powders, rather like very fine chalk and coal dust. Each capsule is sandwiched between transparent electrical contacts, and electricity can be used to draw the black particles to either the top or the bottom of the capsule, so that appears black or white when you look at it from above. If the ‘paper’ is covered with lots of tiny electrodes, each one can turn that part of the paper black or white and back again. The e-ink can be switched as many times as you like, spelling out different patterns of black and white – different words, for example, or grainy images like newspaper photos. So far, researchers have only made quite crude ‘grids’: the black and white patches are big. But in principle they could be made very small, like the pixel grids of a laptop computer screen. A single sheet of this electronic paper could show you an entire library, page by page.
Lecture 4: The Plaster That Stretches Life
Ouch! I’ve cut myself – get a sticking plaster! We’ve all done it, but have you ever thought what a plaster really is? After all, you wouldn’t cover a cut with sellotape, would you? What makes a sticking plaster so good at helping a wound to heal?
Well, it does more than just stick. There are several different materials in a plaster. The main strip is made from cotton or soft plastics such as PVC or polythene. Little holes let moisture out and air in, allowing the wound to ‘breathe’. The most expensive plasters are made from a waterproof but breathable fabric similar to Goretex, which is used for weatherproof clothing.
This strip is coated on one side with a polymer adhesive. (We looked at these in The Trainer That Ran Over the World.) Plasters have to be sticky enough to stay put, but not so much that you can’t get them off again!
Then there’s a pad of absorbent material, in case the wound still bleeds a little. This is usually made of cotton, impregnated with an antiseptic to stop infection and coated with a non-stick gauze that stops dried blood from sticking to it.
So as we rush for the medical cabinet, it’s a carefully designed object that we grab to patch up our wounded finger. A sticking plaster is really designed to be a kind of artificial skin. Like skin, the plaster is soft and flexible, it lets moisture through, and it stops the wound getting irritated or infected while it heals. Some medical companies sell fast-drying liquids – a kind of flexible superglue – that can be used in place of sticking plasters. These cover small wounds with a thin waterproof layer of polymer that is even more like real skin.
But some wounds need even better protection than this. You can’t cover large, severe skin burns with a plaster. As a burn heals, the patient’s body makes new skin at high speed to cover the wound as quickly as possible. So it doesn’t do a very good job: the skin is papery, inflexible and disfiguring, and is called scar tissue.
Some burn wounds can be covered with skin grafts: patches of skin taken from other parts of the patient’s body. But this might not be possible if the burns are too big. So scientists have made various types of artificial skin from plastics and other polymers, which protect bad burn wounds and help to reduce scarring.
Medicine owes an awful lot to chemistry. In 1900 you could expect, on average, to die when you were 45. A hundred years later, you can hope to live to at least 75. And you’ll suffer less during that time – what would it have been like, 200 years ago, to go into a big operation without any anaesthetics or pain killers? In those days medicine was like torture.
These improvements in health are partly thanks to all sorts of new chemicals: new drugs to prevent or cure disease, new materials and instruments for surgery – and also simple stuff that helps us stay clean and healthy, such as soaps, disinfectants and toothpaste.
Soap story
The ancient Romans had a huge empire and stacks of gold, but they probably smelt terrible. They didn’t know how to make soap – only the Gauls of northern Europe, who the Romans called dirty barbarians, knew that.
Soap is clever stuff, because it makes grease dissolve in water. If you get butter (which is greasy) on your fingers, you can’t wash it off under the tap. But if you rub them with soap first, the grease disappears. Soap is made of tadpole-shaped molecules which have a part that dissolves in water (the ‘head’) and a part that dissolves in oil and grease (the ‘tail’). When soap meets grease, the tails stick into it, leaving the heads poking out at the surface. This gives a blob of grease a water-soluble coat. It disguises the grease as something that ought to dissolve in water. And so it does. Soaps are sometimes called detergents.
You probably don’t wash your hair with toothpaste or clean your teeth with shampoo. But they both contain the same kinds of detergent. If you take a look at the list of ingredients on a few bottles or tubes, you’ll probably soon find the chemicals sodium lauryl sulphate or ammonium lauryl sulphate. These are similar to the molecules in soap, with the same ability to surround oils and fats in a water-soluble coat. Detergents like this create a soapy foam when you rub shampoo into your hair or brush your teeth.
But there’s obviously more to shampoo and toothpaste than that. Both are concocted from many ingredients to make them more effective and more appealing. In shampoo, chemical additives make sure that the mixture has the right acidity. A very mildly acidic shampoo smoothes down the tiny scales on the surface of your hairs and makes the strands look lustrous. Other ingredients give it the right consistency – about as thick as warm honey – and add pleasant smells and colours.
Toothpaste isn’t just a sweetened soap; it is also an abrasive, like very fine grit. It contains a powder of a mineral-like substance, such as calcium carbonate (chalk). The grains grind away when you brush to remove plaque from your teeth. Chemicals containing fluoride are added to make your tooth enamel harder and more resistant to decay. Flavourings make the toothpaste taste nice (minty, banana, you name it), and the whole mixture is thickened into a stiff paste. It’s certainly an improvement on the days when people had to brush their teeth with baking soda, which killed off bacteria and prevented decay but tasted pretty foul.
Cell wars
The ancient Romans had a huge empire and stacks of gold, but they probably smelt terrible. They didn’t know how to make soap – only the Gauls of northern Europe, who the Romans called dirty barbarians, knew that.
Even a simple medical operation could be fatal 100 years ago. It was very hard to prevent wounds from becoming infected by bacteria – and an infection could spread rapidly. Most deaths at that time were caused by bacterial diseases like pneumonia and tuberculosis, which are fairly easy to treat now.
Perhaps the most important advance in chemical medicine (chemotherapy) was the discovery of antibiotics: substances that kill bacteria. The first antibacterial drug, a synthetic red dye called Prontosil Rubrum, was discovered in 1933. It was the first of a class of drugs called sulfonamides, which were later replaced by penicillin, a natural antibiotic discovered in 1928 by Alexander Fleming.
Many living organisms produce antibacterial chemicals to protect themselves, and these have supplied chemists with a rich source of antibiotics. Chemists have improved natural antibiotics by altering their chemical structure to make them more potent. But because antibiotics have been over-used during the past 50 years or so, bacteria have been able to develop resistance to many of them. The more we use antibiotics, the more we give an advantage to natural mutant forms of bacteria that are resistant to them, and so the more they thrive. This is a race we might not win – unless we use these drugs more carefully.
A bacterial or a viral infection creates a full-scale war inside us. The bacteria or viruses are the invaders, seeking to multiply and to colonise our bodies. The cells of our immune system spring to the defence, tracking down and attacking the invaders. In cancer patients, the body is at war with itself: some of our cells have become renegades, multiplying rapidly and paying no heed to what they are supposed to be doing. These cancerous cells grow into deadly tumours.
Drugs generally disrupt these rogue cells or viruses. But often they also wreak havoc where they are not meant to, harming our own healthy cells. This is why antibiotics make us feel so dreadful. Medical scientists would like to deliver drugs more accurately: for example, making sure that they end up in cancer cells and nowhere else. Such a drug would be a ‘magic bullet’, finding its way to the target like a homing missile.
Spare parts
Many people lose limbs because of accidents or war. If they can get an artificial limb at all, it’s usually not much more than a model of the real thing made from metal and plastic. But researchers are hoping that it will be possible soon to make artificial limbs that can be wired up to the brains of their wearers so that they can move and control them just by thinking about it – or even replacement limbs made of real flesh and blood.
Even if we never need an artificial limb, many of us will lose the use of some important part of our body during our lives. Our sight and hearing fade as we get older. Our muscles weaken and our bones get brittle and liable to break if we fall. We might suffer liver or kidney failure; our hearts get weak and jittery. Our blood vessels become hardened and clogged; our minds start to disintegrate.
Sometimes it is possible to put these things right with surgery. Over 20,000 people have now had heart transplants, and hundreds of thousands have been given new kidneys. But transplants don’t always work or last for long, and there are always many more people in need of one than there are donors. So there is a huge demand for artificial organs.
We often think of our heart as our most vital and precious organ. But in fact an artificial heart is one of the easiest organs to make. It doesn’t do anything very complex: it is really just a pump that drives the blood through our veins. Artificial hearts, made mostly from tough and flexible polymers, were developed in the 1970s, and the first artificial-heart transplant was made in 1984, enabling the person who received it to survive for nearly two years. Several hundred people have now received artificial hearts – but only for a short time, to keep them alive while they await the transplantation of a real heart. They’re still just a short-term solution.
The basic problem with any implants like this is that they don’t really fool our bodies. Our cells can tell when they come into contact with a substance that isn’t a natural part of the body. This is why some transplants are rejected by the patient’s immune system: it may be a real kidney, but it’s someone else’s kidney, and that’s not good enough. The body regards anything ‘foreign’ as an invader.
So if we stick a material like a plastic or metal implant in our body, the body goes on the defensive. Our cells might try to break the implant down and dissolve it. If they can’t do that, they will treat the surface of the material as if it is a wound, and start to build up scar tissue around it. We don’t want that to happen.
Biomedical engineers therefore have to disguise implants as well as possible. Take artificial arteries, for instance. They are made from plastics and are surgically inserted to replace the hardened, clogged arteries of patients suffering from the disease called atherosclerosis. But the synthetic materials attract blood cells called platelets, which gather on the surface and start to form new clots and blockages. One way of preventing this is to coat the artificial artery walls with the same anti-clotting agent that is produced naturally by the cells of real arteries.
Kitchen chemistry
What would you rather eat: chips or raw potatoes? Clearly, cooking alters the flavour of foods. This is because the heat causes chemical reactions, changing the substances that the food contains. People sometimes say that chemistry is nothing but cookery, but in fact cooking is just chemistry.
If you have ever tried eating raw potato, you’ll probably agree that chips are sweeter. This is because potato is full of starch, a carbohydrate polymer made from sugar. When it is heated, starch breaks down into sugar. In the hot oil of a chip pan, some of this sugar gets burnt, and the chips turn first yellowish and then brown (and if you forget about them, black). Burnt sugar produces a whole new range of flavour molecules – firstly delicious ones, like those in toffee, but then increasingly bitter ones if the sugar burns too much.
Meat becomes less chewy and more tender as it cooks, because the heat breaks down the stringy fibres of protein. And as the texture improves, so does the flavour. Cooked meat tastes more ‘meaty’ than it does when raw. This change is caused by chemical reactions between the sugars formed from carbohydrates and the amino acids that are produced from the breakdown of proteins.
These reactions were studied in the 19th century by a Frenchman named Louis-Camille Maillard, and they are now called Maillard reactions. There are many different sugars and amino acids, so Maillard reactions in cooked food can generate hundreds or even thousands of different chemical substances, each of which might create its own distinctive flavour. It is this complex blend of flavours that makes well-cooked food so good. Chefs have to be skilled at controlling these reactions to get the best result – they won’t know exactly what all the molecules are in their final dish, but we can all tell when the mixture is right!
Making food feel good
Have you ever eaten a biscuit that’s been left on the plate overnight? Not very nice, is it? It absorbs moisture and goes soggy, and then it’s just not the same. It’s not really the flavour that alters, but the texture – we want our biscuits to be brittle and crumbly, not soft and squidgy. What food feels like has a big effect on how much we enjoy it.
For ice cream, texture is crucial. Ice cream is basically frozen custard; but what makes it irresistible is the way it is frozen. It has to be beaten as it freezes, which does two things: it whips the creamy mixture into a kind of foam, and it stops big crystals of ice from growing. If we just let the liquid ice cream mixture freeze, it would turn into a solid block of creamy ice that wouldn’t taste the same at all.
According to legend, ice cream was invented by horsemen in Mongolia, who rode around the freezing land with a milky yoghurt drink in their saddlebags. As the drink froze, the shaking prevented the ice crystals from getting too big, so the result was a perfect mixture of light, creamy slush.
You don’t have to ride around the Mongolian wasteland, however – popping the mixture in the freezer will do, as long as you stir it occasionally to break the crystals up (see Recipe for ice cream). If you’re in a hurry, you can freeze ice cream in a few seconds using liquid nitrogen, which is very cold indeed: minus 196 oC.
Ice cream manufacturers are now investigating whether they might use a magic ingredient for keeping crystals small, so that the texture won’t be lost if the ice cream starts melting and is then re-frozen. This ingredient is a kind of antifreeze.
The antifreeze liquid that is mixed with water in car radiators stops the water from freezing in winter. But the antifreeze that ice-cream makers are interested in using isn’t like this. After all, they don’t want to prevent ice cream from freezing altogether; they just want to control how that happens, so that the ice crystals don’t get too big. It might be possible to do this by adding so-called antifreeze proteins, which allow crystals to form but make it hard for them to grow.
The big freeze
Such proteins are produced by fish that live in cold water, to stop their blood from freezing. Some plants, such as carrots and buckwheat, also make antifreeze proteins. These molecules have shapes that clip in place on the surface of ice. So once an ice crystal starts to grow, it gets coated with antifreeze proteins which stop it from getting any bigger.
Tiny ice crystals in the blood needn’t be fatal – it’s only when they become large that the serious problems start. There are two main reasons why freezing isn’t good for us. First, it can make us dehydrated by drawing water out of our cells. Secondly, ice crystals are sharp and pointy, and as they grow they can puncture and slice open our cell walls.
This is why it is so hard to preserve living organisms by freezing them. In principle, freezing could create a kind of suspended animation – the organism doesn’t die, but just stops moving until it is thawed. But in practice, freezing causes irreparable damage, so the organism can’t be revived.
Some people hope that human bodies, if frozen immediately after they die, might be preserved intact until a future time when medicine has advanced enough to thaw the bodies out, put right what went wrong, and restore them to life. This is called human cryopreservation.
But it is a vain hope. We don’t yet know enough about how to protect our tissues from ice-induced damage to freeze a person in a way that could really allow them to be brought back to life. Their bodies will suffer too much harm from the freezing process. Maybe as we learn more about how other organisms control freezing, we might be able to reduce this damage. But it’s not clear whether genuine cryopreservation of humans will ever be feasible. And if it was, would you want it? Would you want to wake up in 200 years’ time?
[Box 1: position next to Making food feel good text near ice cream ]
Recipe for ice cream
You need:
4 egg yolks
500 ml milk
120 g sugar
Vanilla essence
500 ml single or double cream
Whisk the egg yolks and the milk, and add the sugar and a few drops of vanilla essence. Heat slowly, stirring, until the mixture is thick enough to coat the back of the spoon. Then leave to cool and stir in the cream. Put in a bowl in the freezer, taking it out to stir every 10-20 minutes, until frozen. You can also add puréed fruit before freezing, or other flavours.
Glossary
adhesive: a substance that sticks two surfaces together. Glues are generally permanent adhesives, which turn solid to create a long-lasting bond.
antibiotic: a chemical that kills bacteria.
atoms: the smallest pieces of normal matter. All substances are made of atoms, joined or stacked together in various ways. Atoms are extremely tiny: a row of ten million of them would be around a millimetre long.
biodegradable: able to be broken down by living organisms. Biodegradable materials fall apart in the environment, eaten up by microorganisms such as bacteria.
biomimetics: the science of copying nature. By looking at natural materials, scientists can get ideas for how to build better synthetic ones.
chemotherapy: the treatment of illness and disease with chemical drugs.
cryopreservation: preventing substances from decaying by keeping them very cold. Food is preserved this way in freezers. Some people hope that it might one day be possible to preserve human bodies by freezing and later to revive them.
detergent: a substance that cleans by removing dirt. The word comes from a Latin word meaning ‘to wipe off’. Soaps are a kind of detergent.
elastomer: a rubbery material, which can be stretched so that it gets several times longer-but which springs back when you let it go.
elastic: if a material returns to its original shape after being bent, it is elastic. Most materials are truly elastic only if you bend them a little: a metal ruler will spring back if bent slightly, but will stay bent if you bend it a lot. The materials commonly called ‘elastic’ (as in elastic bands) are in fact elastomeric.
fibre optics: light can be sent down fibre-optic cables like water down a pipe. The cables are made of glass or plastics, and their surfaces are like mirrors: once light is inside, it bounces down the fibre but can’t escape until it reaches the other end.
information technology (IT): any kind of technology that sends, stores and handles information. The information – it could be voices or sounds, images, numbers, or text – is usually encoded in electrical or light pulses.
laser: a device that emits a special sort of light, generally in an intense beam. Lasers are usually switched on and off electrically – they convert electrical energy into light energy.
light-emitting diode: an electronic device that emits ordinary light (as opposed to laser light, which has special properties). LEDs aren’t normally as bright as lasers, and their beams spread out more. They are really a kind of longer-lasting and more efficient light bulb.
liquid crystal: a substance whose molecules can move around fairly freely while remaining mostly in the same orientation as all the others. Most liquid crystals are made from rod-like molecules, but some contain disk-like molecules that stack like piles of coins.
material: every substance is a kind of material. Some are solid, like wood, metal, plastics, or stone. Others are liquid, like water, honey or molten plastic. Even gases like air can be considered to be materials.
molecule: a group of two or more atoms joined together by chemical bonds. Some substances aren’t really made of molecules: they are just stacks of individual atoms. Metals are like this, and so are many minerals. But most substances – water, wood, plastics, air – are made up of distinct molecules, containing between a few and a few thousand atoms.
odorant: a chemical substance that stimulates our sense of smell.
photonics: a technology that uses light for sending information or controlling other devices, in much the same way as electronics uses electrical currents.
plastic: this has an everyday meaning and a technical meaning. When we talk about ‘plastics’, we usually mean synthetic polymers (see below), which can range from soft (like polythene) to hard (like polystyrene). But scientists call a material plastic if it can be pushed, pulled, beaten or squeezed to take on another shape. According to this definition, metals are plastic: you can hammer them into new shapes.
polymer: a material whose molecules are made up of many smaller molecules (monomers) linked together. In most polymers, the monomers are joined into long straight chains. But there are other ways of linking them too: into branching chains, for instance, or star shapes. A copolymer is a polymer made from more than one type of monomer.
protein: a natural polymer whose monomers are amino acids. Many proteins contain thousands of amino-acid building blocks. Some proteins, such as enzymes, have compact, scrunched-up chains. Others, such as those in skin and muscle, may have more elongated chains.
semiconductor: a material that conducts electricity, but not very well. A semiconductor contains only a few electrons that are free to move throughout the material, and thus to carry an electrical current. Technically speaking, a semiconductor can be distinguished from a metal by the fact that semiconductors conduct better as they get warmer, whereas metals conduct worse.
silicon chip: a small wafer of silicon carved into electronic circuits. The wires and electrical components in these circuits are made from very thin layers of silicon and other materials ‘painted’ onto the silicon wafer using special chemical processes.
strength: a material is said to be strong if you have to use a big force to break it, for example, by pulling on a rod.
telecommunication: technically, this means ‘communicating over a long distance’. Telephones, television and radio networks are examples of telecommunications systems.
tissue engineering: making living tissues such as skin or organs outside the body by growing cells on a scaffold.
toughness: a material is said to be tough if you have to expend a lot of energy to break it.
transistor: the most important kind of electronic device in electrical circuits like those on silicon chips. Transistors and other devices can be wired together to carry out ‘logic operations’, like adding or subtracting two numbers. These are the basic processes involved in computer processing.
virus: tiny parasites that can cause diseases. Unlike bacteria, viruses don’t really have a life of their own: they live and multiply by invading cells and using the biological ‘machinery’ in these cells to make copies of themselves. Scientists aren’t quite sure whether viruses deserve to be called ‘living’ or not.
Find out more
Books
The Cambridge Guide to the Material World by Rodney Cotterill (Cambridge University Press, 1985)
The Age of the Molecule edited by Nina Hall (Royal Society of Chemistry, 1999)
The Extraordinary Chemistry of Ordinary Things by Carl H Snyder (John Wiley, 1992)
The New Science of Strong Materials by JE Gordon (Princeton University Press, 1984)
Designing the Molecular World by Philip Ball (Princeton University Press, 1994)
Made to Measure: New Materials for the 21st Century by Philip Ball (Princeton University Press, 1997)
Stories of the Invisible: A Guided Tour of Molecules by Philip Ball (Oxford University Press, 2001)
Molecules at an Exhibition by John Emsley (Oxford University Press, 1998)
Nature’s Building Blocks by John Emsley (Oxford University Press, 2001)
The Science of Cooking by Peter Barham (Springer-Verlag, 2001)
Books for younger readers: A Guide to the Elements by Albert Stwertka (Oxford University Press, 1999)
Exploring Chemical Elements and Their Compounds by David L Heiserman (McGraw-Hill, 1991)
Websites
The Royal Institution
Includes a list of the Christmas Lectures since 1825 and details of events for schools.
Royal Society of Chemist
The site of the UK’s main organisation for chemistry and chemical research. Links to news, events, journals.
The UK’s association for chemical industries ranging from agriculture and food to pharmaceuticals and construction. Includes news on education and events.
American Chemical Society
The US organisation for chemical research. Includes a section on educational resources. (See in particular divched.chem.wisc.edu/CHED-resources.html and chemistry.org/portal/Chemistry?PID=educatorsandstudents.html)
Institute of Materials[1] Institute of Materials[2]
Details of materials research in the UK. Has recently affiliated with other institutes to create the Institute of Materials, Minerals and Mining
Materials World
Magazine of the Institute of Materials, with articles (not online) about all areas of materials science.
UK Centre for Materials Education
All kinds of details about educational resources (including a preliminary searchable database), projects, events and a discussion forum.
Materials Research Society
The US materials science organisation, with up-to-the-minute news and links to general information and educational resources.
Challenge of Materials
Educational site about the materials exhibition at the London Science Museum.
Materials Interactive
An educational interactive site about materials and their properties, run by the UK National Physical Laboratory.
Nature Materials portal
Site on materials science run by Nature, with research news and links to the journal Nature Materials.
Chemical elements
Has all the facts and figures about each of the chemical elements. There is a special Scholar Edition designed for schools and universities.