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| FERROFLUIDS |
A quiet revolution is currently under way in labs around the world. Scientists are finding ways to manipulate matter at increasingly small scales, as well as drawing inspiration from biological materials. This revolution is giving us substances with properties that were once confined to the pages of science fiction books.
But these materials are more than just scientific curiosities – they are genuinely useful, to the point that as applications start to emerge they will radically change our world.
Here at Focus we’ve combed research papers and patent applications to bring you the top 10 most influential materials coming your way.
10. FERROFLUIDS
If you were to try to build a real life Terminator T-1000, the shape-shifting robot assassin in Terminator 2, you could do a lot worse than start with a ferrofluid. Just like T-1000, ferrofl uids are a liquid metal that can change shape. Their abilities are down to the fact that they contain microscopic particles of magnetite or hematite, or some other compound containing iron, dispersed in a liquid. As such, this liquid is magnetic, which allows it to be coaxed into position.
Ferrofluids have quietly crept into everyday use. Held in place by magnets, they form a liquid seal around spinning hard drives in computers, preventing debris drifting in and causing your holiday snaps to be wiped. They’re also used in speakers. But they have much greater potential. NASA has been experimenting with them in spacecraft attitude control systems and Canadian researchers say they could be the next generation of telescope mirrors, able to shift their shape to compensate for atmospheric distortion.
One of the biggest areas of potential is medicine. At Virginia Tech in the US, researchers are exploring the use of a ferrofluid containing iron oxide nanoparticles to treat cancer. The fluid would be directed into a tumour by magnets before an oscillating magnetic field is applied. This would cause the ferrofluid to vibrate, generating heat and killing the cancer cells. “The ideal treatment increases the temperature of the tumour cells for about 30 minutes while maintaining the healthy tissue temperature,” says Professor Ishwar Puri who is leading the research. While the technique works, clinical trials are some way off.
APPLICATIONS:
• Spacecraft control
• Telescope mirrors
• Cancer treatment.
9. GOLD NANOPARTICLES
Medieval stained glass artisans were the first nanotechnologists. They may have been completely oblivious to the physics of what they were doing, but their techniques led to tiny particles of gold becoming trapped in glass that emit a ruby red colour. Now, instead of illuminating biblical scenes, gold nanoparticles are to be used in new tests for deadly conditions, such as HIV, that are more sensitive and easier to read than current tests.
At the scale of the very small, the realm of nanotechnology, materials take on new properties. While a solid lump of gold is, well, gold, tiny particles can produce different colours depending on how they clump together. Researchers at Imperial College London have put this to good use. Their HIV testing solution is packed with ions (electrically charged atoms) of gold. When blood serum is dropped into it, what happens next is determined by whether it contains the HIV virus. If it does, put simply, the level of hydrogen peroxide in the solution drops and irregular nanoscopic clumps of gold are produced, producing blue light. If no HIV is present, then the solution becomes awash with hydrogen peroxide and spherical gold nanoparticles are generated, which produce red light.
So sensitive is the test it can detect attograms, or billionths of a billionth of a gram, of HIV protein in a millilitre of human serum, even better than the, ahem, current gold standard. And crucially, the colour change is so distinct it can be read by the naked eye – current tests require expensive machines to read the all-important change of hue.
Professor Molly Stevens, who led the research at Imperial, says a practical test isn’t far off: “So far we have demonstrated a proof of concept including testing with human HIV positive samples. The technology now needs optimising to make it more portable and user-friendly. That could take less than five years.”
What’s more, the test can be altered to detect other diseases such as malaria, prostate cancer and tuberculosis.
APPLICATIONS:
• HIV detection
• Prostate cancer detection
• Tuberculosis and malaria detection.
8. POLYURETHANE BLOCK COPOLYMER
Imagine a material that could stop a speeding bullet travelling at 350 metres per second even when it’s little more than 3cm thick, enveloping it with no marks or cracks in its surface. If this material makes up the windscreen of your presidential limousine or the armoured troop vehicle you’re travelling in, it could just have saved your life. The material in question goes by the uninspiring name of polyurethane block copolymer. Its ability to seal up at the point of entry is explained, according to Professor Ned Thomas, an engineer at Rice University in Houston, by the fact that it melts as the bullet makes contact at high speeds. This seems to play a part in arresting the projectile, dissipating the energy. It then reseals, plugging the gap left behind. This is a sequence of events Thomas has only recently been able to fathom by studying the material under an electron microscope.
As well as bullet-proof glass, polyurethane could end up in body armour and even on the outside of spacecraft and satellites, absorbing space junk and other projectiles that might otherwise cause serious damage. Using a piece of steel with similar dimensions would be less ef ective at stopping fast-moving projectiles as well as being seven times heavier, says Thomas.
APPLICATIONS:
• Jet engine turbine blade protection
• Satellite protection
• Bulletproof windscreens
• Bulletproof armour.
7. METAMATERIAL INVISIBILITY CLOAKS
Metamaterials get their incredible properties not from their many component parts, but from the intricate ways these parts are fashioned. It’s this complicated architecture that gives them properties that aren’t found in nature – metamaterials are strange by definition. “Usually materials scientists are presented with a substance, determine its properties and only then come up with a use for it. But metamaterials work in the opposite direction,” says materials scientist Professor Costas Soukoulis at Iowa State University.
A key target for materials scientists is the invisibility cloak, which would come with a myriad of military and consumer uses. To become a cloak, the metamaterial needs to contain nanostructures that give it a negative refractive index, allowing light to be bent unnaturally so it entirely passes around an object. If done successfully this could render the object, be it an aircraft or even a person, invisible.
As remarkable as this might sound it is not science fiction. Scientists have already demonstrated the principle. So far, however, they have had more success in bending microwaves than visible light. And this wave bending has been achieved with large, desk-mounted constructions that can only make objects of a given dimension disappear.
However, in November 2012, researchers at Yonsei University in Seoul, South Korea, and Duke University in the US announced they have developed a metamaterial cloak that’s able to adapt to changes in the object’s shape. That said, the changes could be no more than 10mm and it still only works with microwave-frequency light. So aircraft will not be disappearing from our skies just yet.
APPLICATIONS:
• Cloaking device
• Optical computing
• Spacecraft infrared heat or cosmic radiation shield
• Medical imaging.
6. PROGRAMMABLE MATTER
The things that currently make up our world are a pre-defined shape, only changing as they weather or decay. But what if our materials were ‘alive’, able to change their form on demand? A screwdriver could turn into a spanner, a fleet of robots could spring into shape in the field of battle after being transported in 2D... and a flat-packed wardrobe could assemble in front of your eyes.
It sounds like the stuf of fantasy, but ‘programmable matter’ could bring such shapeshifting products into our lives. Programmable matter already exists in the labs at Massachusetts Institute of Technology (MIT). Here shape-memory alloys – metals that can change their form when exposed to heat or a magnetic field – are combined with extremely thin electronic circuit boards. These boards provide heat in just the right place to fold the alloys into a pre-defined shape. “This opens the possibility of a world where we are able to program not just computation, but also matter,” says Professor Daniela Rus at MIT, who is leading the research.
Rus and her team have programmed their flat sheets to fold into origami classics such as planes or boats, as well as more complex forms including a functional insectoid robot capable of fetching and carrying. “Instead of carrying a toolbox with lots of specific items in them like screwdrivers and wrenches, you could carry around a small pallet of these sheets that you would use to create something for a particular function,” says Rus.
APPLICATIONS;
• Self-assembling robots
• Universal toolkits.
5. SELF-HEALING CONCRETE
Mixing bacterial spores with concrete sounds like a recipe for structural failure, but it could actually extend the life span of bridges, buildings and roads by up to 40 per cent. And given that US President Obama is currently seeking $50 billion to repair America’s highways, bridges and airports, the benefits of longer-lasting building materials is clear.
At Delft University of Technology in the Netherlands, microbiologist Dr Henk Jonkers has developed a microbe-filled concrete that has a longer life thanks to its innate ability to repair itself, microcracks spontaneously disappearing. While cracks of less than 0.4mm tend not to reduce overall strength, they can allow the ingress of water, which can both weaken the concrete when it freezes and carry damaging substances inside.
“We add a ‘healing agent’ to the concrete mixture, composed of bacterial spores – dormant bacteria – and a suitable feed surrounded by a coating,” says Jonkers. When a crack occurs, it breaks open the spores and the feed. “Incoming water activates the spores, converting them into active bacteria, which turn the feed into limestone.” The species of bacteria used, Bacillus cohnii and Bacillus pasteurii, are not harmful and are adapted to the highly alkaline conditions within the concrete. They convert the calcium lactate feed into tough calcium carbonate. Outdoor tests still need to be carried out but if successful, self-healing concrete could be in production in just four years.
APPLICATIONS:
• Tunnels
• Viaducts
• Roads
• Marine structures.
4. DNA HYDROGELS
Adding water to something usually makes it runnier. But when water is added to one new material, it spontaneously takes on a new shape. Welcome to the weird world of DNA-filled hydrogels.
Hydrogels are highly absorbent, sponge-like networks of polymers that readily absorb up to 100 times their mass in water. They are already found in some contact lenses and in the conducting sticky pads on EEG heart monitors. But at Cornell University in the US, Professor Dan Luo – a specialist in putting DNA to unusual uses – has been adding synthetic strands of genetic material to these gels.
In a demonstration, Luo and his team created hydrogels in moulds shaped like the letters DNA. When they poured the gels out, they formed amorphous blobs. But when water was added, the gel formed into the letters again. The DNA becomes entangled inside the gel, behaving a little like rubber bands glued together.
DNA strands will lock onto other strands with complementary coding. By designing genetic material that links in specific ways, the team hopes to tune the gel’s properties.
The hydrogel could be used in medicine – a drug-infused gel would fit a wound exactly. It could even be used in electronics as a water-activated switch. In one test at Cornell, a gel infused with metal particles was placed between two electrical contacts, conducting electricity. When water was added, the gel shortened and the contact was lost.
APPLICATIONS:
• Scafolds for tissue engineering
• Drug-filled wound plugs
• Water-activated switches.
3. IONIC LIQUIDS
Take some table salt, heat it to 800°C and you’ll see something curious. Instead of blackening and giving of noxious fumes, it will just melt and turn to liquid without any chemical decomposition, much like an ice cube turning to water. In this form, the salt is remarkably good at dissolving stuff.
Now imagine a similar substance, but one that melts at room temperature and you’ll have a good idea of what an ionic liquid, or fluid salt, is like. Unlike the vast majority of the multibillion-dollar industrial solvents that keep the modern world ticking over, ionic liquids don’t form vapours. This may not sound like the most exciting of properties but it means they’re far less dangerous and polluting than many current chemical staples. It makes them useful as charge-carrying liquids in devices like batteries and low-cost solar cells because their stability means they will last longer.
Besides being capable of dissolving almost anything, ranging from the dangerous bacterium MRSA to poisonous mercury found in natural gas, ionic liquids are also likely to lead to the development of a raft of new chemical products because of the unusual ways they react with other materials.
One of the most promising uses of ionic liquids is for storing hydrogen as fuel for eco-friendly cars. Currently, hydrogen is stored as a compressed gas in high-pressure tanks. But this requires a large tank to hold enough hydrogen for a long journey. An ionic liquid could store a lot of hydrogen in a small space, releasing it when required by the onboard fuel cell.
The possibilities seem endless. “Wherever a conventional liquid can be used, it can in principle be replaced by an ionic liquid designed to be better,” says Professor Ken Seddon, co-director of the Queen’s University Ionic Liquid Laboratory in Dublin. It’s little wonder that this year, ionic liquids topped the Great British Innovation Vote run by the Science Museum.
APPLICATIONS:
• Green cleaning solvent
• Fuel cells for cars
• Solar cells.
2. GRAPHENE
One material has become synonymous with the word ‘miracle’: graphene. A new potential use of this two dimensional sheet of pure carbon is announced almost weekly. Ten thousand research papers were published last year on graphene.
According to Professor Andre Geim at the University of Manchester, who won the Nobel Prize for Physics in 2010 for co-discovering it, it is the strongest material ever measured, the stifest material we know and has the largest surface area-to-weight ratio, with one gramme capable of covering several football pitches. Graphene’s ultra-thin structure also gives it interesting electrical properties – it’s highly conductive for starters.
Unknown 10 years ago, research on graphene was awarded 1 billion Euros earlier this year, so great is its promise. Products containing graphene are starting to creep onto the market – a tennis racket made by Australian manufacturer Head being among these trailblazers. A glance at the list of the top 10 graphene patent applicants, which includes Samsung, SanDisk 3D (which makes 3D circuits) and Xerox, provides an indication of where it will have the biggest impact on our lives.
Until very recently graphene may well have taken the top spot of our Wonder Materials line-up – it’s certainly worthy. But there’s a new kid on the materials block that just pipped it to the post.
APPLICATIONS:
• Flexible computer displays
• Faster microprocessors
• Stronger, lighter composites (tennis rackets and bikes)
• More efficient solar cells
• Sensors
• Medical imaging
• Flexible batteries.
1. SILICENE
Since its discovery in 2004, graphene has been basking in the materials science limelight. But a substance with a similar-sounding name, silicene, will ultimately take the glory by revolutionising the electronics industry.
“Silicene is the silicon counterpart of graphene,” explains Associate Professor Yukiko Yamada-Takamura at the Japan Advanced Institute of Science and Technology who is a world leader in silicene research. Where graphene is a single layer of carbon atoms, silicene is a single layer of silicon.
In many ways silicene behaves like graphene – it is highly electrically conductive for instance, allowing electrons to flow through it almost unhindered. But it has a crucial advantage over its carbon counterpart – being silicon-based it is highly compatible with existing silicon circuitry. That means less research time to bring new silicene-based products to market and lower manufacturing costs. It will also have the same benefits as graphene – fast computational speed and little energy lost as heat. So in the long run it will be silicene supercharging your smartphone, not graphene.
Silicene also beats graphene in its structural flexibility. Whereas graphene can only take one form, with its atoms in a specific horizontal lattice, silicene is different. “Silicene can be flexible at the scale of the atom, so the atoms can be displaced out of the plane,” says Yamada-Takamura. These subtle shifts in silicene’s atomic structure mean its electrical properties can be changed, increasing the number of potential uses.
Silicene’s moment of glory is some way of – it was only created for the first time last year by researchers in Germany. That’s a far cry from the raft of graphene-led patents that have already been registered around the world. But ultimately, it is silicene that will have the biggest impact on our lives.
APPLICATIONS:
• Electronic chips
• Digital storage
• Catalysts for mopping up pollution.
By Duncan Graham-Rowe in "BBC Focus Science and Technology, issue 256, July, 2013. Adapted and illustrated to be posted by Leopoldo Costa.