GraphExeter—the bestknown roomtemperature transp

first_img GraphExeter—the best-known room-temperature transparent conductor—is a material built up of several graphene sheets with a layer of ferric chloride molecules in between each sheet. Exeter’s device converts light into electrical signals by exploiting the unique attributes of this material. Says Exeter physics professor Saverio Russo, “This new flexible and transparent photosensitive device uses graphene and graphExeter to convert light into electrical signals with efficiency comparable to that found in opaque devices based on graphene and metals.” At just a few atoms thick, it is ultra-lightweight and portable. Applications? How about photovoltaic textiles that enable your clothes to act as solar panels and charge your mobile phone while you’re walking down the street? Or an intelligent window that can both harvest electricity and display images, all while remaining transparent to the outside? “Smart clothing”—that can monitor a wide range of our functions as we go about our daily lives—is another recent development. Normally, it’s created by weaving conductive materials into fabrics. But that results in flexibility limitations, and it can only be achieved when the conductors are integrated into the design of the clothing from the start. But now, scientists at the UK’s National Physical Laboratory (NPL) have come up with a way to print silver directly onto fibers. The technique involves chemically bonding a nano‐silver layer onto individual fibers to a thickness of 20 nanometers, so that the conductive layer fully encapsulates fibers and has good adhesion and excellent conductivity. Chris Hunt, NPL’s lead researcher on the project, says: “The technique has many potential applications. One particularly exciting area is wearable sensors and antennas which could be used for monitoring, for example checking on patients and vulnerable people; data capture and feedback for soldiers in the field; and performance monitoring in sports. It offers particular benefits over the ‘weaving in’ approach, as the conductive pattern and flexibility ensures that sensors are always positioned in the same location on the body.” Or, how about having a touchscreen on your shirt sleeve? Further possibilities for printed metal inks are being pursued. Scientists at the American Chemical society have employed copper nanosheets, which are inexpensive and highly conductive, as a flexible circuit ink. They took the copper nanosheets, coated them with silver nanoparticles, and incorporated this material into an ink pen, using it to draw patterns of lines, words, and flowers on regular printer paper. Then, to show that the ink could conduct electricity, they connected a battery and lit up an LED at the drawing’s center. Courtesy Northwestern University The battery will continue to work—illuminating that LED—even when stretched, folded, twisted, or mounted on a human elbow. Power and voltage are similar to a conventional lithium-ion battery of the same size. It will stretch up to 300% of its original size with no loss of efficiency and can function for eight to nine hours before it needs recharging, which can be done wirelessly. So far, batteries—which presently power nearly all portable devices—have maintained their edge over supercapacitors for a couple of reasons. One, they’re way cheaper. And two, supercapacitors have low energy density, meaning that the amount of energy they can store per unit weight is relatively small. On the plus side, supercapacitors can be charged quickly and don’t lose their storage capabilities over time. They can literally last for millions of charge/discharge cycles without losing energy-storage capability, whereas the same process in batteries is slow and degrades their internal chemical compounds over time. Should supercapacitors overcome their deficiencies, however, they could be the wave of the future… in which case, we will need flexible ones. A group at the University of Delaware is experimenting with just such a device, using carbon nanotube macrofilms, polyurethane membranes, and organic electrolytes. Research is in the early stages, but the group says that the supercapacitor it’s developed in the lab has achieved excellent stability in preliminary testing. Meanwhile, a team of researchers at the Leibniz Institute for Solid State and Materials Research in Dresden announced last year that they have created a powerful micro-supercapacitor, just nanometers thick and less than half a centimeter across. And it’s bendable. Tests on the new device showed that the tiny power supply can store more energy and provide more power per unit volume than state-of-the-art supercapacitors. Team members are now working on ways to bring down its cost. Another power source that can be harnessed is the sun, through a flexible, transparent, photosensitive device developed at the University of Exeter in England. The device converts light into electrical signals by exploiting the unique properties of two “miracle” carbon-based materials: graphene and graphExeter (developed at the eponymous university). Carbon is a unique element in that its atoms can arrange themselves in many different ways (tubes, spheres, sheets, cubes, meshes), known as allotropes. Each of them, from graphite to diamonds, has distinctive properties. As depicted below, graphene is a carbon allotrope in which the atoms are arranged in a single layer in one plane. It is the thinnest known conductive material. “C’mon Sis, quit crumpling my computer!” It may seem unlikely that those words might soon issue from a young fellow’s mouth. Yet they could, in the not-too-distant future. And it’s because of the hottest trend in consumer products today: Flexible electronics. Some stunning advances in materials technology have made possible a lot of things we never expected to see (or maybe only dreamed of). They are about to lead to a flood of everyday electronic items that you can bend, stretch, crumple, and fold (but not spindle or mutilate). This is a big, big business. One analysis projects that the global flexible electronics market will reach $13.23 billion by 2020, at an estimated CAGR of around 22%. And that’s probably conservative. There’s so much going on in this sector that it’s hard to decide where to begin. But that crumply computer is as good a jumping-off point as any. Remember the old days, when people read newspapers on the train to work, then rolled them up and stuffed the parts they weren’t finished with into their back pockets? The newspaper of the future is going to be kinda like that. Neatly rollable, adaptable to a back pocket. It’s just not going to be made of paper. A September 2013 article from Science Daily asks us to envision “an electronic display nearly as clear as a window, or a curtain that illuminates a room, or a smartphone screen that doubles in size, stretching like rubber.” At UCLA, for example, scientists have fabricated “an elastomeric polymer light-emitting device (EPLED)” that can be repeatedly stretched, folded, and twisted at room temperature while still remaining lit and holding its original shape. The material has a single layer of electro-luminescent polymer sandwiched between a pair of transparent elastic composite electrodes that are made of a network of silver nanowires inlaid into a rubbery polymer. (The EPLED is a type of polymer light-emitting electrochemical cell [PLEC] device. Research is also ongoing in the development of flexible versions of organic light-emitting diode [OLED] displays commonly found in today’s smartphones, but the UCLA team chose PLECs instead because they’re easier to fabricate and simpler to work with.) The developers stretched and re-stretched their PLEC display 1,000 times, extending it 30% beyond its original shape and size, and it still continued to work at a high efficiency. In another test to determine the material’s maximum stretch, the researchers found it could be stretched to more than twice its original size while still functioning. It can also be folded 180° and twisted in multiple directions. Qibing Pei, UCLA’s principal investigator on the project says confidently that “[W]e believe that fully stretchable interactive displays that are as thin as wallpaper will be achieved in the near future.” Roll up the news and take it with you? That may not be far off. Samsung is also working on a flexible screen. The company is mounting its display on silicone that can be bent in half 100,000 times (Samsung claims), yet suffer a loss of light intensity in the crease zone of just 6%—all but undetectable by the human eye. Think of a smartphone whose screen size could be doubled by simply unfolding it. And the technology can be adapted to simple lighting, too. Is this your next desk lamp?center_img Of course, as our electronics become flexible, so must their power supplies, especially in the case of mobile devices. How that power is delivered will depend on how the war between batteries and supercapacitors is ultimately resolved. But scientists are currently working on flexible versions of both. In early 2013, collaborating researchers from Northwestern and the University of Illinois unveiled the first stretchable lithium-ion battery. American Chemical Society To test the ink’s flexibility, the researchers folded the paper 1,000 times, even crumpling it up, and demonstrated that the ink maintained 80-90% of its conductivity. But perhaps the most exciting roles flexible electronics will be playing in the years to come are in the realm of medicine. Because the human body is always in motion, the design of wearable health monitors and implants must take that into account. Yong Xu of Wayne State University has pushed the research forward by inventing a method for fabricating high-performance and high-density semiconductor circuits, and bonding them to flexible substrates. “The ultimate goal is to develop flexible and stretchable systems integrated with electronics, sensors, microfluidics, and power sources, which will have a profound impact on personalized medicine, telemedicine, and health care delivery,” Xu says. Surgery could be transformed. Consider what happens today after a doctor operates to remove a tumor from a patient’s liver. Even after following up with radiation and/or chemotherapy, the surgeon can never be positive that the treatment was successful. “But,” says Tom Jackson, an engineering professor at Penn State, “suppose I could apply a flexible circuit to the liver and image the tissue. If we see a new malignancy, it could release a drug directly onto that spot, or heat up a section of the circuit to kill the remaining cancerous cells. And when we were done, the body would resorb the material. “What I want is something that matches the flexibility and thermal conductivity of the body,” and conventional silicon technology is too rigid and thermally conductive for work like that. Jackson is going to get what he wants. Yes, conventional silicon tech is inappropriate for many uses in and on the body. But might there be a new form of silicon that captures its stability, efficiency, and low cost, yet bends and stretches? Indeed there is, says John Rogers, a cutting-edge materials scientist at the University of Illinois Urbana-Champaign. Rogers’ team has found a way to trick silicon into a more malleable form. Rather than making transistors from conventional wafers, they slice the material into sheets several times thinner than a human hair. “At this scale,” Rogers says, “something that would otherwise be brittle is completely floppy … [in the way that] a 2-by-4 is rigid, but a sheet of paper is not—similar materials, just different thicknesses.” The applications he’s working on are truly mind-blowing. Here are just a few: Imagine a sensor array that can precisely mold to the shape of an organ. Start with the heart. Sensors made of a stretchable, lightweight material and embedded with electronics could wrap around a beating heart like a glove, providing real-time measurements of cardiac activity. The goal, Rogers says, is to detect early signs of arrhythmia and deliver coordinated voltages across the entire organ, rather than administering massive shocks at a few points, as current defibrillators do. Collaborators at Washington University in St. Louis have tested the device, which he calls an “artificial pericardium,” on rabbits and on human hearts removed from transplant recipients. Trials in live patients could be just around the corner. He and his colleagues have also created an electronic “second skin.” It’s a wireless circuit board less than a micron thick that can be stamped directly onto the skin and sealed with a spray-on bandage. The device could enable doctors to monitor a wide range of biological functions, including heart rate, skin temperature, muscle activity, and hydration, for starters—and it conforms so well to the shifting creases and troughs of human skin that it can stay on for up to two weeks before it is sloughed off. It can also send small electric currents to stimulate muscles as part of a physical therapy regimen. And its noninvasiveness makes it especially useful in neonatal care. Finally, Rogers is well on the way to developing Prof. Jackson’s desired resorbable devices. These “transient electronics,” as he calls them, could monitor and prevent infection at surgical sites, then melt away according to a set schedule of days or weeks. And—made up of ingredients found in antacids and vitamin pills—they’re harmless to the human body. During a talk at an electrical engineering conference, a skeptical colleague bet Rogers that he wouldn’t dare swallow one of his transient devices on stage. Rogers won that bet. The shift to flexible electronics is a trend that means a financial windfall for companies poised to cash in on it. One of them—our July recommendation—presently sits in the BIG TECH portfolio. This company makes equipment used to encapsulate organic light-emitting diodes, part of the process that enables electronics to be folded or rolled. As demand for flexible devices takes off, so too will demand for this company’s equipment. For access to this recommendation, simply sign up for a risk-free 90-day trial of BIG TECH.last_img

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