Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World

by Mark Miodownik

But there is a catch. The energy of the light has to match exactly that required for the electron to move from its seat to a seat in the available row.

The way these quanta are arranged in glass is such that moving to a free row requires much more energy than is available in visible light.

Higher-energy light, on the other hand, such as UV light, can upgrade the electrons in glass to the better seats, and so glass is opaque to UV light. This is why you can’t get a suntan through glass, since the UV light never reaches you.

Pyrex is a glass with boron oxide added to the mix. This is another molecule that, like silicon dioxide, finds it hard to form crystals. More importantly, as an additive it counteracts the tendency of glass to expand when heated or contract when cooled.

Glass equipment is the workhorse of the chemist’s world—so much so that every professional chemical lab has a glass blower in residence. How many Nobel Prizes did this material make possible? How many modern inventions started life in a test tube?

One of the great attractions of glass is that its shiny bright appearance makes it seem clean even if it isn’t, a collective deception we all accept in order to avoid thinking too much about using the same glass that was in a stranger’s mouth perhaps only an hour before.

I was constantly being dragged to museums as a child, to the national this or that, and without exception I was bored in all of them. I tried to do what the adults did and walk around in ponderous silence or ruminate in front of a painting or a sculpture, but it didn’t work for me.

This new type of jewel thief was imbued with the virtues of diamond itself: elegant, sophisticated, and unadulterated. In films such as To Catch a Thief and The Pink Panther, diamonds play the role of a princess cruelly imprisoned. Upstanding members of society by day, cat burglars by night, their rescuers were played by film stars like Cary Grant and David Niven. In these films, a diamond robbery is portrayed as a noble act. The diamond thief is light on his or her feet and requires only a black catsuit and a knowledge of sophisticated stately homes and combination safes located behind paintings. In contrast, the stealing of cash or gold from a bank or train was depicted as a grubby crime, often carried out by brutish and greedy men.

The problem faced by the company DeBeers, which in 1902 controlled 90 percent of the world’s diamond production, was how to sell to this much bigger market without devaluing the gems in the process. They managed it through a cunning marketing campaign: by concocting the phrase “Diamonds are forever,” they invented the idea of the diamond engagement ring as the only true way to express everlasting love.

But diamonds are not forever, at least on the surface of this planet. It is, in fact, diamond’s sibling structure, graphite, that is the more stable form, and so all diamonds, including the Great Star of Africa in the Tower of London, are actually turning slowly into graphite.

The conundrum can be explained by noting that within the graphite layers each carbon atom has three neighbors with which it shares its four electrons. In the diamond structure, each carbon atom shares its four electrons with four atoms. This gives the individual graphite layers a different electronic structure and stronger chemical bonding than diamond. The flip side, though, is that each atom in graphite has no electrons left over to form strong bonds between its layers. Instead, these layers are held together by the universal glue of the material world, a weak set of forces generated by fluctuations in the electric field of molecules, called van der Waals forces. This is the same force that makes Blu-Tack sticky. The upshot is that when graphite is put under stress, it is the weak van der Waals forces that break first, making graphite very soft. This is how a pencil works: as you press it on the paper you break the van der Waals bonds and layers of graphite slide across one another, depositing themselves on the page. If it weren’t for the weak van der Waals bonds, graphite would be stronger than diamond. This was one of the starting points for Andre Geim’s team.

The reason why graphite is metallic while diamond is not is also its hexagonal atomic structure. As we have seen, in the diamond structure, all four electrons in each carbon atom are partnered up with a corresponding electron. In this way, all atoms in the lattice are strongly held in a bond, and there are no “free” electrons. This is the reason why diamonds do not conduct electricity, because there are no electrons free to move within the structure to carry the electric current. In the graphite structure, on the other hand, the outer electrons do not just bond with a counterpart electron in a neighboring atom but rather form a sea of electrons within the material. This has several effects, one of which is to allow graphite to conduct electricity, since the electrons can move around like fluid. Graphite was used by Edison for the first light bulb filaments because it also has a high melting point, which allows it to glow white hot without melting when a high current passes through it. Meanwhile, the sea of electrons also acts as an electromagnetic trampoline for light, and this reflection of light is what makes it appear shiny like other metals. This neat explanation of graphite’s metallic properties is not what won Andre Geim’s team a Nobel Prize, though. It was merely their starting point.

Antoine Lavoisier did just this in 1772 and found that diamond burns when it gets red hot, leaving nothing. Nothing at all.

What Lavoisier did next makes my heart sing, such is the elegance of the experiment. He heated diamond in a vacuum so that there, with no air to react with the diamond, it might survive to higher temperatures. It’s one of those experiments that is easy to propose but much harder to carry out, especially in the eighteenth century, when vacuums themselves were not so easy to produce. What happened next astounded Lavoisier: the diamond still wasn’t impervious to red heat, but this time it turned into pure graphite—proof that these two materials were indeed made of the same stuff, carbon.

Lavoisier and countless others across Europe searched for a way to reverse the process, to turn graphite into diamond. Vast wealth would be the reward for anyone who could do it, and the race was on. But the task was a formidable one. All materials prefer to change from less stable to more stable structures, and because the diamond structure is less stable than graphite’s, it requires very high temperatures and pressures to persuade it to change in the opposite direction. These conditions exist inside the Earth’s crust, but it still takes billions of years to grow a big diamond crystal. Simulating the conditions in a laboratory is extremely difficult. Claim after claim was made and then retracted. None of the scientists involved got massively rich overnight, which some said was further evidence of their failure. Others suspected that those who did achieve the feat of transformation kept quiet and got rich slowly.

Now the synthetic diamond industry is indeed big business, but it does not compete head to head with the natural diamond jewelry industry. There are a few reasons for this. The first is that although the industrial process has been mastered to the extent that small synthetic diamonds can be produced more cheaply than mining real ones, they are mostly colored and flawed, since the accelerated process of making them introduces defects which color the diamonds. In fact, the majority of these diamonds are used in the mining industry, where they embroider drills and cutting tools, not for aesthetic effect but to enable them to cut through granite and other hard rocks.

In 1967 it was discovered that there is a third way of arranging carbon atoms that produces an even harder substance than diamond. The structure is based on graphite’s hexagonal planes but modified to be three-dimensional. This structure, called lonsdaleite, is thought to be 58 percent harder than diamond, although it exists in such small quantities that it is hard to test. The first sample was found in the Canyon Diablo meteorite, where the intense heat and pressure of impact transformed graphite into lonsdaleite.

Carbon fiber, as they named it, was made by spinning graphite into a fiber. By rolling sheets of this material up, with the fibers running lengthwise, they could take advantage of the huge strength and stiffness within the sheets. The weakness, as with pure graphite, still lay in the material’s structural dependence on van der Waals forces, but this was overcome by encasing the fibers in an epoxy glue. A new material was born: carbon fiber composite.

(the recent Boeing Dreamliner is 70 percent carbon fiber composite),

The concept, which was developed in 1960 by a Russian engineer, Yuri Artsutanov, would require the construction of a thirty-six-thousand-kilometer-long cable connecting a satellite to a ship floating in the ocean at the Earth’s equator. All studies indicate that the idea is mechanically feasible but requires the cable to be made from a material with an extraordinarily high strength-to-weight ratio. The reason why weight comes into it, as with any cable structure, is that it must first be able to hold its own weight without snapping. At thirty-six thousand kilometers long, you would need a material so strong that a single thread of it could be used to lift an elephant. In practice even the best carbon fiber thread could only lift a cat. But this is because it is full of defects. Theoretical calculations make clear that if a completely pure carbon fiber could be engineered, then its strength would be much higher, exceeding the strength of diamond. The search was on to find a way to make such a material.

A clue to how this might be done came with the discovery of a fourth carbon structure, one that was found in the most unlikely of places: the flame of a candle. In 1985 Professor Harry Kroto and his team discovered that inside a candle flame carbon atoms were miraculously self-assembling in groups of exactly sixty atoms to form super-molecules of carbon. The molecules looked like giant footballs and were nicknamed “buckyballs” after the architect Buckminster Fuller, who had designed geodesic domes with the same hexagonal structure. Kroto’s team received the 1996 Nobel Prize for chemistry for this discovery, and also woke everyone up to the fact that the microscopic world might contain a whole zoo of other carbon structures that had never been seen before.

Almost overnight carbon became one of the sexiest topics in materials science, and soon another type of carbon emerged, a carbon that could form tubes that are only a few nanometers wide. Despite the complexity of their molecular architecture, these carbon nanotubes had a peculiar property: they could self-assemble.

Carbon nanotubes are like miniature carbon fibers except that they have no weak van der Waals bonding. They were found to have the highest strength-to-weight ratio of any material on the planet, which meant that they might be strong enough to build a space elevator. Problem solved? Well, not quite. Carbon nanotubes are, at most, a few hundred nanometers in length, but they would need to be meters in length to be of use.

Just for starters, graphene is the thinnest, strongest, and stiffest material in the world; it conducts heat faster than any other known material; it can carry more electricity, faster and with less resistance, than any other material; it allows Klein tunneling, an exotic quantum effect in which electrons within the material can tunnel through barriers as if they were not there. All this means that the material has the potential to be an electronic powerhouse, possibly replacing silicon chips at the heart of all computation and communication. Its extreme thinness, transparency, strength, and electronic properties mean also that it may end up being the material of choice for touch interfaces of the future, not just the touch screens we are used to but perhaps bringing touch sensitivity to whole objects and even buildings. But its most intriguing claim to fame is that it is a two-dimensional material. This doesn’t mean it has no thickness, but rather that it cannot be made any thicker or thinner and be the same material. This is what Andre’s team showed: add an extra layer of carbon to graphene and it goes back to being graphite, take a layer away and the material does not exist at all.

Of all places, the oven is where ceramics should be comfortable, because that’s where they were formed, but terra cotta fails time and time again. The reason is that liquid seeps into its pores and then expands into steam when heated, turning the pore into an exploding micro-crack that eventually links up with other micro-cracks like tributaries of a river, and finally erupts on the surface of the terra cotta dish, spelling an end not just to the dish but, as often as not, to the meal within it, too.

Unlike metals, plastics, or glass, ceramics cannot be melted and poured. Or rather, we don’t have the materials that can withstand the temperatures required to contain such liquids. Ceramics are made from the same stuff as mountains, rocks, and stone, whose liquid form is the lava and magma of the Earth. But even if lava could be captured and poured into a mold, it would not form a strong ceramic—certainly not one that you would recognize or make a cup from. What forms is, of course, volcanic rock, which is full of holes and imperfections. It takes millions of years of heat and pressure deep inside the Earth to turn such stuff into the so-called igneous rocks and stones that make up mountains. For these reasons, attempts to make artificial substitutes for rock either use chemical reactions, which is how cement and concrete work, or, in the case of pottery, involve heating up clay in a furnace, not to melt it, but instead to take advantage of a very unusual property of crystals.

Clay is a mixture of finely powdered minerals and water. Like sand, these mineral powders are the result of the eroding action of the wind and water...

When this is heated up, the first thing that happens is that the water evaporates, leaving the tiny crystals aggregated in a kind of sand castle with lots of holes where the water used to be. But at high temperatures something special happens: atoms from one crystal will jump on to another nearby crystal and then back again. The atoms in some crystals, however, do not return to their original position, and gradually bridges of atoms are built between the crystals. Eventually, billions of such bridges are built, and the collection of crystals has become something more like a single continuous mass.

Usually, when the crystals are cold, these atoms don’t have enough energy to move around and do something about their predicament. But when the temperature is high enough, the atoms can move around: they set about reorganizing themselves so that as few of them as possible are forced to inhabit a position at the surface of the crystal—so that, in fact, there is less surface overall. In doing so, they reshape the crystals to fit together as fully and economically as possible, eliminating the holes between them. Slowly but surely the collection of tiny crystals become a single material. It’s not magic, but it is magical.

It was the potters of the East who solved the problem of fragility and porosity. Their first step was to realize that if earthenware was covered with a particular kind of ash, this ash would transform during firing into a glass coating that would stick to the outside of the pot. This glass skin would seal all the pores on the outside of the earthenware. And by varying the composition and distribution of the glaze, the pots could be colored and decorated.

While glazing prevents water from getting into fired clay, it doesn’t solve the problem of porosity within the body of the ceramic, which is how the cracks start in the first place. So tiles are still relatively weak, as are glazed terra cotta cups and bowls. This problem was also solved by the Chinese, but it involved the creation of a completely new type of ceramic altogether.

No doubt they tried all sorts of different mixtures, but eventually they hit upon a particular combination of kaolin and a few other ingredients, such as the minerals quartz and feldspar, which created a white clay and, when fired, a nice-looking white ceramic. This was no stronger than earthenware, but, unlike any other clay they knew, if they increased the temperature of the furnace to a very hot 1300°C, it did something strange. The clay turned into an almost watery-looking solid: a white ceramic that had a near perfectly smooth surface. It was quite simply the most beautiful ceramic that anyone had ever seen. It was also stronger and tougher than any ceramic had any right to be. It was so strong that cups and bowls could be made that were extremely thin, almost as thin as paper, without compromising their ability to withstand cracks. These cups were so fine that they were translucent. It was porcelain.

Then, as the temperature increased further still to 1300°C and the whole kiln became white hot, the magic would have started to happen: some of the atoms flowing between their crystals would have turned into a river of glass. Now they were mostly solid, but also part liquid. It would have been as if the cups had blood running through their veins in the form of liquid glass. This liquid would have flowed into all the small pores between the crystals and coated all the surfaces. Now, unlike almost all other types of ceramic, the cups would have felt what it was like to be free of defects.

The ringing sound of a cup is the clearest and surest way to know whether it is fully formed inside. If there are any defects within it, any holes that were never filled by the river of glass that flowed while they were white hot, then these will absorb some of the sound and prevent it from reverberating. Such a cup sounds dull. But a fully dense cup rings and rings and rings.

Despite playing such a vital role in our joints, ligaments lack a blood supply, and so once they have snapped it is virtually impossible to grow them back.

Our bodies are very picky about materials inserted into them. Most things are rejected, but titanium is one of the few metals they will tolerate. More than that, titanium will undergo osseointegration, which means that it will form strong bonds with living bone. This is useful if you want to tether a piece of hamstring to a bone and be sure that the bond will not weaken and loosen with time. My titanium screws are still in place more than ten years later, and because of titanium’s remarkable combination of strength and chemical inertness—there are very few metals that do not react in some way with the body; even stainless steel is not impervious to the chemical rigors of life within the body—they should be in pristine condition. Thanks to its strong surface coating of titanium oxide, titanium can last a lifetime, and I am certainly hoping it will last mine. Titanium can also withstand high temperatures, and so the screws are likely to be the last recognizable part of me once I die and am cremated.

once you’ve lost the use of your hip, knee, elbow, or any other joint, no amount of rest and immobilization is going to solve the problem.

What is required is the erection of a temporary structure within the joint that mimics some of the basic internal architecture of cartilage. Introducing chondroblast cells into such a scaffold, as it is called, allows them to grow and divide and increase their population, and in doing so gives them time and space to rebuild their habitat, and so regrow cartilage. The neat thing about this scaffolding approach is that either the cells themselves can consume the scaffold or it can be designed to dissolve once the cells have finished building their habitat, leaving pristine cartilage within the knee or hip.

The role of adult stem cells is to renew our tissues, and each type of cell has an equivalent stem cell to produce it. The stem cells that produce bone cells are called mesenchymal stem cells. Having built the scaffold, Professor Seifalian’s team implanted it with mesenchymal stem cells taken from the patient’s bone marrow and placed the whole object into the bioreactor. These stem cells then turned into a range of different cells that started to build cartilage and other structures, creating a living, self-sustaining cellular environment, while at the same time dissolving the scaffold around them. Eventually, all that was left was a new windpipe.

Types of artificial heart have been developed, but the longest anyone has survived with one is a year.

This is because much of what makes us older is not the age of our cells but the deterioration of the systems that generate them. Aging is the cellular equivalent of playing telephone: each generation of cells does not quite regenerate the structure it inherited and so mistakes and imperfections creep in. My skin has aged not because my skin cells are forty-three years old—they are not; they are constantly being replaced with new cells generated by my adult stem cells—but because, over time, problems and imperfections have developed in the structure of my skin and have then been passed from one generation of cells to the next. Spots form, the skin thins, wrinkles appear. These problems will continue to be reproduced.

Already robotic limbs have been developed to replace those lost by amputees. These electro-mechanical devices pick up the nerve impulses delivered to the missing body part by the brain and translate them into the equivalent hand grips or leg movements in the artificial limb. The same technology has now been used to help those who are paralyzed from the neck down to control robotic limbs and regain a measure of independence. Although these technologies are designed for those disabled or paralyzed, they could also be used by someone who has lost movement as a result of aging.

On Earth, ninety-four different types of atoms naturally exist, but eight of these elements make up 98.8 percent of the mass of the Earth: iron, oxygen, silicon, magnesium, sulfur, nickel, calcium, and aluminum. The rest are technically trace elements, including carbon. We have the technology to transform some of the common ones into the rare ones, but this requires a nuclear reactor, which costs even more money than mining and results in radioactive waste. This is essentially why gold is still valuable in the twenty-first century. If gathered together, all the gold ever mined would fit inside a large town house. Nevertheless, the rarity of certain types of atoms on the planet, such as neodymium or platinum, which are so technologically useful, may not ultimately be a problem, because a material is not defined by its atomic ingredients alone.

The possibilities seem limitless, but what is more interesting is that many of the structures at this scale self-assemble. That means that the materials are able to organize themselves. This might seem spooky but is perfectly in line with the existing laws of physics. The crucial difference between the car motor and a nano-motor is that in the case of the nano-version the physical forces that dominate at that scale, such as electrostatic and surface tension forces, which can pull things together, are very strong, while gravitational forces are very weak. At the scale of a car, by far the strongest force is the gravitational force of the Earth, which pulls the various bits of the motor apart. The result is that nano-machines can be designed to assemble themselves using electrostatic and surface tension forces (and heal themselves in the same way). Much of this molecular machinery already exists inside cells, which is how they can assemble themselves, whereas at the human scale we need things like muscles and glue.

These so-called meta-materials can be formed with variable refraction indices, which means they can bend light any way they want to. This has yielded the first generation of invisibility shields, which when surrounding an object bend light around it so that from whichever direction you try to observe it, it appears to vanish.

But as the scale chart shows, living matter is, in some sense, no different conceptually from non-living matter. What dramatically distinguishes the two is that in living materials we find there is an extra degree of connectivity between the different scales: living materials actively organize their internal architecture. They do this by setting up communication between the different scales of the organism. In a non-living material, a mechanical stress imposed at the human scale has all sorts of effects at different scales, causing many internal mechanisms to react in response: as a result it might change shape or break or resonate or stiffen. A living material, on the other hand, can detect that such a stress is occurring and adopt a course of action in response: it might push back, or it might instruct the whole organism to run away. Obviously there is a vast range of such animated behaviors: the branch of a tree behaves passively, as if it were an inanimate material, most of the time, while the leg of a cat is most definitely animate most of the time. One of the biggest questions in science is whether communication between the scales combined with active responses is a sufficient explanation of what makes something alive. Such a hypothesis is not meant to downgrade the importance of living beings but rather to upgrade inanimate materials: they are much more complex than they appear.