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Preventing glass from fogging or frosting up is a longstanding challenge with myriad applications: eyeglasses, cameras, microscopes, mirrors and refrigerated displays, to name but a few. While there have been many advances in meeting this challenge, so far there has been no systematic way of testing different coatings and materials to see how effectively they work under real-world conditions.
Now, a team of MIT researchers has developed such a testing method, and used it to find a coating that outperforms others not only in preventing foggy buildups, but also in maintaining good optical properties without distortion. The surface is made by a process called layer-by-layer deposition. In this case, alternating layers of two different polymers — poly(vinyl alcohol) and poly(acrylic acid) — are deposited on a glass surface. “The magic of what we do is nanoscale processing,” Rubner explains: producing the layers so as to control their properties almost down to the level of individual molecules.
This production process appears relatively easy and inexpensive to carry out on large scales. “These are common polymers,” Rubner says. “They’re well-known and cheap, but brought together in a unique way.”
To test the effectiveness of this material, and that of many other alternatives, the team devised a set of extreme tests. For example, they kept samples of the material at minus 20 degrees Celsius for an hour, then exposed them to a very humid environment. While untreated glass, or glass treated with conventional hydrophilic or hydrophobic coatings, quickly develops a layer of frost following such treatment, glass with the new treatment remains clear. However, it still appears to be hydrophobic in the presence of large water droplets.
To measure its performance, Lee says, the researchers photographed the glass slides under carefully controlled conditions. “We developed a protocol … [that] allows us to detect how good one coating is in comparison with another,” he says.
Previous testing typically measured the light transmitted through the glass after exposure to humidity, but failed to measure the level of image distortion caused by water condensation. “We came up with a way to measure them not just for transmission, but also distortion,” Lee says.
While the new coating outperforms others, it does have one drawback: It’s vanishingly thin, so could be vulnerable to aggressive cleaning or mechanical challenges. For this reason, it may not be useful for applications where it is exposed to harsh environments or to excessive wiping.
Another limitation is that the new coating only prevents small amounts of frost buildup; it wouldn’t work where there’s a continuous source of cold water, such as for deicing an airplane wing, Rubner says.
Glass doesn't have to be brittle. Scientists propose a way of predicting whether a given glass will be brittle or ductile—a property typically associated with metals like steel or aluminum—and assert that any glass could have either quality. A Yale University team and collaborators propose a way of predicting whether a given glass will be brittle or ductile—a desirable property typically associated with metals like steel or aluminum—and assert that any glass could have either quality. Ductility refers to a material's plasticity, or its ability to change shape without breaking. "Most of us think of glasses as brittle, but our finding shows that any glass can be made ductile or brittle," said Jan Schroers, a professor of mechanical engineering and materials science at Yale, who led the research with Golden Kumar, a professor at Texas Tech University. "We identified a special temperature that tells you whether you form a ductile or brittle glass." The key to forming a ductile glass, they said, is cooling it fast. Exactly how fast depends on the nature of the specific glass. Focusing on a new group of glasses known as bulk metallic glasses (BMGs)—metal alloys, or blends, that can be extremely pliable yet also as strong as steel—researchers studied the effect of a so-called critical fictive temperature (CFT) on the glasses' mechanical properties at room temperature. When forming from liquid, there is a temperature at which glass becomes too viscous for reconfiguration and freezes. This temperature is called the glass transition temperature. Based on experiments with three representative bulk metallic glasses, the researchers said there is also, for each distinct alloy, a critical temperature that determines the brittleness or plasticity of the glass. This is the CFT. Researchers said it's possible to categorize glasses in two groups—those that will be brittle because in liquid form their CFT is above the glass transition temperature, and those that will be ductile, because in liquid form their CFT is below the glass transition temperature. They previously thought a liquid's chemical composition alone would determine whether a glass would be brittle or ductile. "That's not the case," Schroers said. "We can make any glass theoretically ductile or brittle. And it is the critical fictive temperature which determines how experimentally difficult it is to make a ductile glass. That is the major contribution of this work." The finding applies theoretically to all glasses, not metallic glasses only, he said. "A glass can have completely different properties depending on the rate at which you cool it," Schroers said. "If you cool it fast, it is very ductile, and if you cool it slow it's very brittle. We anticipate that our finding will contribute to the design of ductile glasses, and in general contribute to a deeper understanding of glass formation."
A new type of material that halts and absorbs light may lead to advances in solar energy, stealth technology, and other fields, experts report. Researchers ath the University at Buffalo developed a “hyperbolic metamaterial waveguide” that halts and ultimately absorbs each frequency of light, at slightly different places in a vertical direction, to catch a “rainbow” of wavelengths. The technology is essentially an advanced microchip made of ultra-thin films of metal and semiconductors and/or insulators. “Electromagnetic absorbers have been studied for many years, especially for military radar systems,” says Qiaoqiang Gan, an assistant professor of electrical engineering at University at Buffalo. “Right now, researchers are developing compact light absorbers based on optically thick semiconductors or carbon nanotubes. However, it is still challenging to realize the perfect absorber in ultra-thin films with tunable absorption band. “We are developing ultra-thin films that will slow the light and therefore allow much more efficient absorption, which will address the long existing challenge.” Light is made of photons that, because they move extremely fast, are difficult to tame. In their initial attempts to slow light, researchers relied upon cryogenic gases, which are very cold—roughly 240 degrees below zero Fahrenheit—and difficult to work with outside a laboratory. Gan previously helped pioneer a way to slow light without cryogenic gases. He and other researchers at Lehigh University made nanoscale-sized grooves in metallic surfaces at different depths, a process that altered the optical properties of the metal. While the grooves worked, they had limitations. For example, the energy of the incident light cannot be transferred onto the metal surface efficiently, which hampered its use for practical applications. Researchers say the technology could lead to advancements in an array of fields. For example, in electronics there is a phenomenon known as crosstalk, in which a signal transmitted on one circuit or channel creates an undesired effect in another circuit or channel. The on-chip absorber could potentially prevent this. The on-chip absorber may also be applied to solar panels and other energy-harvesting devices. It could be especially useful in mid-infrared spectral regions as thermal absorber for devices that recycle heat after sundown, Gan says. Technology such as the stealth bomber involves materials that make planes, ships, and other devices invisible to radar, infrared, sonar, and other detection methods. Because the on-chip absorber has the potential to absorb different wavelengths at a multitude of frequencies, it could be useful as a stealth-coating material.
Generally, hardware upgrades incrementally — processors slowly gain more cores, graphics cards slowly become more powerful, and storage devices slowly gain more capacity. Hardware rarely upgrades with a significant leap, jumping from one form to another that is so significantly upgraded that it barely resembles what came before it. These leaps do happen though — in just a matter of a few years dumbphones evolved into smartphones and a great deal of laptops become super slim tablets. Now, utilizing a new type of magnetoelectric material, computer memory may take that significant leap.
Via Szabolcs Kósa
Any kid can blow a soap bubble, but only a physicist would think to electrify one. Left to its own devices, a bubble will weaken and pop as the fluid sandwiched between two thin layers of soap succumbs to gravity and drains toward the floor. But when researchers trapped a bubble between two platinum electrodes (pictured) and cranked up the voltage, the fluid reversed direction and actually flowed up, against the force of gravity. The newly strong and stable bubbles could live for hours, and even visibly change colors as their walls grew fatter, the team reports in the current issue of Physical Review Letters. Because soap film is naturally only nanometers thick, this whimsical experiment could help scientists create more efficient labs-on-chips, the mazes of nanotunnels that can diagnose disease based on the movements of a miniscule drop of blood.
New polymer aerogels from NASA Glenn Research Center are flexible and 500 times stronger than traditional aerogels. The new class of polymer aerogels also have superior mechanical properties. For example silica aerogels of a similar density have a resistance to comperession and tensile limit more than 100 times smaller than the new polymer aerogels. The image above shows a Smart car parked on top of a thick piece of NASA's new polymer aerogel. Silica aerogels would crush to powder if placed under a car tire. As seen above, the same is not true of the new polymer aerogels, even if the car is only a Smart car. Overall, the mechanical properties are rather like those of a synthetic rubber, save that the aerogel has the same properties (and far smaller thermal conductivity) with only about 10 percent of the weight. Applications in clothing as well as insulation of pipes, buildings, water heaters, and the like are enabled by these materials. Tents and sleeping bags can also benefit from the combination of light weight and thermal insulation. NASA is even considering the new polymer aerogels for use asinflatable heat shields. The practicality of many such applications will depend on the cost of polymer aerogel in commercial quantities. In any case, these types of products now have another dimension of design flexibility.
Software can transform a computer from a word processor to a number cruncher to a video telephone. But the underlying hardware is unchanged. Now, a type of transistor that can be switched with magnetism instead of electricity could make circuitry malleable too, leading to more efficient and reliable gadgets, from smart phones to satellites. Transistors, the simple switches at the heart of all modern electronics, generally use a tiny voltage to toggle between ‘on’ and ‘off’. The voltage approach is highly reliable and easy to miniaturize, but has its disadvantages. First, keeping the voltage on requires power, which drives up the energy consumption of the microchip. Second, transistors must be hard-wired into the chips and can’t be reconfigured, which means computers need dedicated circuitry for all their functions. The ability of a magnetic logic gate to hold the switch on or off without a voltage “could lead to great reduction of energy consumption”, says study co-author Jin Dong Song, a physicist at KIST. Even more impressively, the magnetic switches “can be handled like software”, he says, by simply flipping the field to enable or disable a circuit. Thus a mobile phone could, for example, reprogram a bit of its microcircuitry to process video while its user watched a clip on YouTube, then switch the chip back to signal processing to take a phone call. This could greatly reduce the volume of circuitry needed inside the phone. Such reconfigurable logic could be invaluable in satellites, adds Mark Johnson of the Naval Research Laboratory in Washington DC, a co-author of the paper. If part of a chip failed in orbit, another sector could simply be reprogrammed to take over. “You’ve healed the circuit and you’ve done it from Earth,” he says. To really catch on, however, the magnetic logic would have to be integrated with existing silicon-based technologies. That may not be easy. For one thing, indium antimonide, the semiconductor crucial to the circuits, doesn’t lend itself well to manufacturing processes used to make modern electronics, according to Junichi Murota, a researcher working with nanoelectronics at Tohoku University in Japan. But Johnson says that it may eventually be possible to build similar bridges with silicon.
Researchers at the National Institute of Standards and Technology (NIST) have shown that by bringing gold nanoparticles close to the dots and using a DNA template to control the distances, the intensity of a quantum dot's fluorescence can be predictably increased or decreased. Their research was published in Angewandte Chemie. This breakthrough opens a potential path to using quantum dots as a component in better photodetectors, chemical sensors and nanoscale lasers. Anyone who has tried to tune a radio knows that moving their hands toward or away from the antenna can improve or ruin the reception. Although the reasons are well understood, controlling this strange effect is difficult, even with hundred-year-old radio technology. Similarly, nanotechnology researchers have been frustrated trying to control the light emitted from quantum dots, which brighten or dim with the proximity of other particles. The NIST team developed ways to accurately and precisely place different kinds of nanoparticles near each other and to measure the behavior of the resulting nanoscale constructs. Because nanoparticle-based inventions may require multiple types of particles to work together, it is crucial to have reliable methods to assemble them and to understand how they interact. The researchers looked at two types of nanoparticles, quantum dots, which glow with fluorescent light when illuminated, and gold nanoparticles, which have long been known to enhance the intensity of light around them. The two could work together to make nanoscale sensors built using rectangles of woven DNA strands, formed using a technique called "DNA origami."
In 2011, a Corning researcher named Terry Ott faced a problem that nobody else had needed to solve in the company’s 160-year history: how to make sheets of glass that could be rolled onto spools. The challenge arose because Corning had developed a new kind of glass, known as Willow, which is as thin as a sheet of paper and acts a bit like it, too—if you shake it, it will rattle, and it can bend enough to be spooled. It could be the basis for displays in thinner, lighter cell phones and tablets—or for entirely new products, like displays that fit the curve of your wrist. Inventing the glass was an achievement in itself for Corning, which also makes the durable Gorilla Glass used in Apple’s iPhone and other mobile devices. But Willow, which is one-third as thick as Gorilla Glass, would be a meaningless breakthrough if Corning couldn’t figure out how to make it in large quantities—and in a way that customers could use on their own production lines. The way Corning solved the problem of mass-producing Willow helps illustrate the extent to which technological innovation depends on close connections between R&D and manufacturing. Some of the work was straightforward: Willow is made with Corning’s core manufacturing technology, a process called fusion forming, which involves heating glass in a trough. At the right temperature, the molten glass will evenly pour over the sides and then solidify at the bottom, where it can be drawn downward into a vertical sheet and then cut. But to get Willow made in continuous sheets, Ott’s team had to figure out the proper rate at which to draw the glass out after it fused, so that the surface quality would be consistent. The process of getting the glass onto rollers also required new equipment. And Ott’s team had to develop thin plastic tabs to line the edges of the glass and keep it from touching anything on the rollers, which could create defects in its surface. The tabs are applied to Willow’s edges as the glass is being drawn.
Researchers from North Carolina State University have developed elastic, self-healing wires in which both the liquid-metal core and the polymer sheath reconnect at the molecular level after being severed. “Because we’re using liquid metal, these wires have excellent conductive properties,” says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper on the work. “And because the wires are also elastic and self-healing, they have a lot of potential for use in technologies that could be exposed to high-stress environments.” The researchers first created tiny tunnels, called microfluidic channels, in a commercially available self-healing polymer using solid wire. By filling those channels with a liquid-metal alloy of indium and gallium, they were able to create a liquid-metal wire in an elastic sheath. Because the wire is liquid, it can be stretched along with the polymer sheath. When the wires are sliced or severed, the liquid metal oxidizes – forming a “skin” that prevents it from leaking out of its sheath. When the severed edges of the wire are placed back together, the liquid metal reconnects and the sheath re-forms its molecular bonds.
Researchers have created a dc invisibility cloak made of a metamaterial that not only shields an object almost perfectly, but at 1-cm thick is also the thinnest cloak ever constructed, reaching the ultimate limit of thinness for artificial materials. As the first invisibility cloak that combines both near-perfect performance and extreme thinness, it could open the doors to practical applications. In the past, invisibility cloaks have been too large to be used in many real-world applications. The key to making a material that can prevent another object from being seen—or from being detected by electromagnetic waves in any way—is to control two material parameters: electric permittivity and magnetic permeability. Electric permittivity corresponds to the degree to which a material permits the formation of an electric field within itself, while magnetic permeability corresponds to the degree to which a material can be permeated by a magnetic field.
As the researchers explain, a perfect invisibility cloak must have a permittivity and permeability that are both strongly anisotropic (directionally dependent) and inhomogeneous (made of different materials). A metamaterial with these parameters is currently beyond the reach of current technology. However, by loosening these strict requirements, researchers have been able to fabricate metamaterials that mimic these properties and can be used as imperfect invisibility cloaks. The researchers hope that this invisibility cloak could make it possible to realize a variety of applications, such as electric impedance tomography (EIT), a medical imaging technique that can detect cancer. Another application could be cloaking or detecting land mines. "Electrostatics has wide potential applications in EIT technology, graphene, natural resource exploration, and underground archaeology," Cui said. "In our paper, we designed and fabricated a dc cloak, which is possible to be used in such potential applications. The dc cloak may be used to cloaking the landmines to make them invisible. Knowing the physical principle, we may also find ways to detect the cloaked landmines."
In the near future, the researchers plan to study three-dimensional ultra-thin dc cloaks and ultrathin cloaks for harmonic fields.
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Manish Dhane
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Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage. Researchers at MIT have discovered a new state of matter with a new kind of magnetism. This new state, called a quantum spin liquid (QSL), could lead to significant advances in data storage. QSLs also exhibit a quantum phenomenon called long-range entanglement, which could lead to new types of communications systems, and more. Generally, when we talk about magnetism’s role in the realm of technology, there are just two types: Ferromagnetism and antiferromagnetism. Ferromagnetism has been known about for centuries, and is the underlying force behind your compass’s spinning needle or the permanent bar magnets you played with at school. In ferromagnets, the spin (i.e. charge) of every electron is aligned in the same direction, causing two distinct poles. In antiferromagnets, neighboring electrons point in the opposite direction, causing the object to have zero net magnetism (pictured below). In combination with ferromagnets, antiferromagnets are used to create spin valves: the magnetic sensors used in hard drive heads. In the case of quantum spin liquids, the material is a solid crystal — but the internal magnetic state is constantly in flux. The magnetic orientations of the electrons (their magnetic moment) fluctuate as they interact with other nearby electrons. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” says Young Lee, senior author of the research. It is these strong interactions that apparently allow for long-range quantum entanglement.
The United States military is reportedly backing a Canadian company's development of a material that can render soldiers invisible, according to news reports. Maple Ridge, B.C.-based Hyperstealth Biotechnology has developed "Quantum Stealth," a type of camouflage that bends light around the wearer or an object to create the illusion of invisibility. President and CEO Guy Cramer likened the new technology to Harry Potter's invisibility cloak during a recent CNN appearance, and described its ability to easily and effectively hide a soldier in different environments. "Unless you walked right into them, you wouldn't know that they were there," Cramer said. The material doesn't require batteries, projectors or cameras. It is also inexpensive and lightweight, according to Hyperstealth's website. For security reasons, the company will not provide public demonstrations, only mockup photos. But Canadian military groups and the U.S. Federal Emergency Response Team have seen the technology and can back up his claims. Cramer described the material's incredible value to soldiers who carry out operations during the day, or those who are trying to evade their enemy, the Daily Mail reported. Beyond that, the technology could have use on a larger scale, on submarines, tanks or aircrafts.
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A 4D printing process is demoed at TED which could herald an age of self-assembled objects say experts. Many are only just getting their heads around the idea of 3D printing but scientists at MIT are already working on an upgrade: 4D printing. At the TED conference in Los Angeles, architect and computer scientist Skylar Tibbits showed how the process allows objects to self-assemble. It could be used to install objects in hard-to-reach places such as underground water pipes, he suggested. It might also herald an age of self-assembling furniture, said experts. TED fellow Mr Tibbits, from the MIT's (Massachusetts Institute of Technology) self-assembly lab, explained what the extra dimension involved. "We're proposing that the fourth dimension is time and that over time static objects will transform and adapt." The process uses a specialised 3D printer made by Stratasys that can create multi-layered materials. It combines a strand of standard plastic with a layer made from a "smart" material that can absorb water. The water acts as an energy source for the material to expand once it is printed. "The rigid material becomes a structure and the other layer is the force that can start bending and twisting it," said Mr Tibbits. "Essentially the printing is nothing new, it is about what happens after," he added. Such a process could in future be used to build furniture, bikes, cars and even buildings, he thinks. For the time being he is seeking a manufacturing partner to explore the innovation. "We are looking for applications and products that wouldn't be possible without these materials," he added. "Imagine water pipes that can expand to cope with different capacities or flows and save digging up the street."
Bulk metallic glasses, referred to commonly as metallic glasses, are technically defined as alloys with critical cooling rates low enough to allow the formation of layers of over 1mm in thickness. Colloquially, they are a metallic alloy that exploits the favorable properties of both metals and glasses, including flexibility, strength, and durability. Ordinary metals are crystalline solids, with high density, conductivity, and strength. Their molecules are ordered in a lattice structure, and disruptions in that lattice structure are known as dislocations. Common metals have approximately one dislocation in one billion molecules, or 10^14 dislocations in a cubic centimeter. It is these dislocations, rather than the natural ordering of metals, that ultimately define the properties of metals. Glasses, on the other hand, are amorphous, or non-crystalline, solids. As anyone who has broken a window knows, glasses are brittle when solid; however, they become molten and exhibit fluid properties at high temperatures. This characteristic, known as the “glass transition,” allows glasses to be molded into creative and complex shapes. These physical characteristics of glass and metals significantly affect their processing potential. During processing, metals display plasticity – the permanent deformation of the metal material. Glasses, however, with no lattice structure or dislocations, instead displays elasticity – a reversible deformation of the material under a force. Both plastic deformation and elastic deformation are necessary when shaping complex objects, yet neither glass nor metal can fully encompass both properties. This is where bult metallic glasses come into play. “We combine two previously mutually exclusive properties,” remarked Jan Schroers, Associate Professor of Mechanical Engineering & Materials Science at Yale University, resulting in the metallic alloys known as bulk metallic glasses. Joining advanced structural properties – strength, durability, and deformation – with the flexibility sufficient for molding complex shapes, these bulk metallic glasses are a ‘super-metal’ of sorts, an enhanced alloy with a range of capabilities.
The secret of invisibility cloaks lies in engineering a material on a scale smaller than the wavelength of the waves it needs to manipulate. The appropriate sub-wavelength structures can then be arranged in a way that steers waves. A group from the Institut Fresnel in Marseille and the ground improvement specialist company, Menard, both in France, recently reported that they have built and tested a seismic invisibility cloak in an alluvial basin in southern France. That’s the first time such a device has been constructed. The French team created its so-called metamaterial by drilling three lines of empty boreholes 5 metres deep in a basin of silted clay up to 200 metres deep. They then monitored the area with acoustic sensors. The experiment consisted of creating waves with a frequency of 50 Hertz and a horizontal displacement of 14 mm from a source on one side of the array. They then measured the way the waves propagated across it.
The French team say its metamaterial strongly reflected the seismic waves, which barely penetrated beyond the second line of boreholes.
The metamaterial is designed to work at the specific wavelength used in the test andseismic waves cannot be guaranteed to have this same wavelength. But by matching the array to the resonant frequency of a building, the thinking is that it could still provide some protection.
There are important caveats, however. One problem with this kind of array is that the reflected waves could end up doing more damage to buildings nearby. That’s why some groups are looking at metamaterials that absorb energy rather than steer or reflect it.
Nevertheless, there are bound to be installations that could benefit from this kind of protection. And since creating these arrays looks relatively simple, it looks to be only a matter of time before we will see them in action for real.
More info: arxiv.org/abs/1301.7642: Seismic Metamaterial: How to Shake Friends and Influence Waves?
Mussels secrete a protein that helps them stick to underwater surfaces like rock, metal, or wood. Chemists have designed sticky polymers that mimic this protein, but these materials quickly set when exposed to air. To get more control with these adhesives, researchers from Japan have developed amussel-mimicking polymer that sets only when hit by light. The polymer could be used as an adhesive for biomedical devices such as stents, the researchers say. Mussel adhesion proteins are sticky because of an unnatural amino acid called 3,4-dihydroxy-L-phenylalanine, or L-DOPA. Oxygen in seawater oxidizes the catechol side chain of this amino acid, producing a benzoquinone group. Then lysines in the protein can attack the benzoquinone, connecting protein chains and forming a gel that attaches the bivalve to a surface. Because catechol groups oxidize quickly, synthetic polymers that mimic the mussel proteins form a gel within minutes of being exposed to air. Atsushi Takahara, at Kyushu University, and his colleagues wanted to control the timing of gel formation. So they synthesized an acrylamide polymer containing catechols protected by o-nitrobenzyl groups to prevent oxidation. When hit with light, these nitrobenzyl groups cleave themselves off the catechol groups, allowing the polymer to be oxidized. The new polymer set within 30 minutes after exposed to high-intensity visible light from a mercury-xenon lamp. To test the polymer’s adhesive strength, the team sandwiched the material between two glass plates, triggered gel formation with light, and then tried to pull the glass plates apart. The shear strength of the glue was similar to that of other commercial medical adhesives, such as ones used to seal cuts.
Research conducted at Princeton and Rutgers Universities offers hope of synthetic catalysts that could produce hydrogen from water more efficiently. Hydrogen is often hailed as a promising environmentally-friendly fuel source, but it is also relatively expensive to produce. However, new research conducted at Princeton University and Rutgers University poses the opportunity to produce hydrogen from water at a lower cost and more efficiently than previously thought possible. The research, led by Princeton chemistry professor Annabella Selloni, takes its inspiration from nature – or more specifically, a bacteria that produces hydrogen from water by using enzymes known as di-iron hydrogenases. Selloni and her fellow scientists made use of a computer model to work out how they could incorporate this function of the enzymes into practical synthetic catalysts, in order to enable humans to produce hydrogen from water. In a paper published in the Proceedings of the National Academy of Sciences of the United States of America, Selloni and her co-authors detail how they made changes to existing water-to-hydrogen catalysts, which are often blighted by a susceptibility to oxygen poisoning. While aiming to improve the stability of the structure in water, the team happily fell upon a catalyst which also appears to be tolerant to oxygen, and without sacrificing efficiency. The new artificial catalyst could be produced from abundant and inexpensive components like iron, offering a potentially cheap method of producing hydrogen. The next step for Selloni and her team is to move the research beyond computer models into the real world, and to this end, they hope to eventually produce a working catalyst which produces vast quantities of inexpensive hydrogen for use as a fuel source.
A study in which chemical compounds are prompted to self-form into crystals could be a step toward creating self-repairing smartphone screens, experts say, or even body armor. Showing that microscopic particles can be made to come together or break apart on their own "opens a new area for design and production of novel and moving structures," wrote the study authors, a team of physicists and chemists from New York University and Brandeis University in Waltham, Mass. The researchers said they were inspired by the way flocks of birds and schools of fish are able to move as if they are a single living organism. The team wanted to see if they could duplicate — and control — that collective motion using non-living objects. The objects they used were made of simple chemicals including sodium, iron, chloride, oxygen and hydrogen. Roughly the size of a single bacterium, they included a piece of the mineral hematite that jutted out, like the front of a car. The researchers placed hundreds of these particles into a drop of a liquid solution on a glass slide. One of the ingredients in the solution was hydrogen peroxide, which is like fuel to a piece of hematite when it's exposed to blue-violet light. Without the specialized light, the particles pretty much vibrated in place like so many tiny idling engines. When the scientists turned on the light, the hydrogen peroxide and hematite began a chemical reaction that propelled the particles forward. The scientists watched under a microscope as, at first, the particles moved about at random. Then, about 25 seconds into the chaos, the limited space and directionless driving produced a traffic jam of particles, said study leader Jeremie Palacci, a postdoctoral fellow at NYU. The jammed particles forced themselves against each other in the pattern of a crystal, each dot surrounded by six others in a hexagonal shape. When they reached a certain size, some of the particles on the edge broke off and grew into other crystals, which slowly moved about. When the blue-violet light was switched off, it took about 10 seconds for the crystals to dissolve. In additional tests, the researchers induced a magnetic field in the liquid to see if they could steer the crystals in a particular way. They found that the iron in the particles was drawn toward the magnetic field, making it possible to control the crystals' movement. Since the crystals are able to sense changes in their environment and move accordingly, they are alive in a fundamental way, the researchers said. "They're flocking," just like birds, said Paul Chaikin, a coauthor of the study and an NYU physicist. Creating materials that can respond to conditions around them is a long-held goal of scientists and engineers working in the field of active materials, said Aparna Baskaran, a physicist at Brandeis who wasn't involved in the study.
Creation of these ultra-thin cardiac patches put medicine a step closer to durable, high-functioning artificial tissues that could be used to repair damaged hearts and other organs.
The cardiac tissue patches utilize a hydrogel scaffolding reinforced by nanomaterials called carbon nanotubes. To create the patches, the researchers seeded neonatal rat heart muscle tissue onto carbon nanotube-infused hydrogels. These novel patches showed excellent mechanical integrity and advanced electrophysiological functions. Moreover, they demonstrated a protective effect against chemicals toxic to heart tissue.
Researchers from the NIST Center for Nanoscale Science and Technology and the Johns Hopkins University have developed a technique to reliably manipulate hundreds of individual micrometer-sized colloid particles to create crystals with controlled dimensions.* The accomplishment is an important milestone for understanding how to direct and control the assembly of microscale and nanoscale objects for nanomanufacturing applications. The experiment uses four electrodes patterned on a microscope coverslip to move the micrometer-sized particles suspended in liquid by applying a combination of AC and DC electric fields. Using a nonuniform, high-frequency AC field, the dielectrophoretic forces exerted on the dielectric particles are tuned to adjust the strength of their attraction to a collection area in the center of the electrodes. When these forces are low enough, electrophoretic-electroosmotic flows induced by applying a DC field allow the researchers to selectively remove particles from the area and trim the particle assemblies to a chosen size and shape. By independently varying the AC and DC electrode potentials, the researchers can direct the self-assembly of two-dimensional (2D) rafts made of precise numbers of particles; i.e., 2D colloidal crystals. Once the desired crystal size is reached, the attractive forces holding the particles in the collection area are increased to stabilize the structure. An important component of this work is the application of a computer vision-based, real-time feedback system that dynamically adjusts the AC and DC fields to automate the directed assembly process. This work shows how the combination of multiple actuators offers extra degrees of freedom that can be used to manipulate ensembles of colloidal components to create desired sizes and shapes. The researchers are now developing measurement methods sensitive enough to track nanometer-scale structures that will allow these methods to be extended to control the assembly of nanoscale materials.
Polymer film that gradually releases DNA coding for viral proteins could offer a better alternative to traditional vaccines. Vaccines usually consist of inactivated viruses that prompt the immune system to remember the invader and launch a strong defense if it later encounters the real thing. However, this approach can be too risky with certain viruses, including HIV.
In recent years, many scientists have been exploring DNA as a potential alternative vaccine. About 20 years ago, DNA coding for viral proteins was found to induce strong immune responses in rodents, but so far, tests in humans have failed to duplicate that success. MIT researchers describe a new type of vaccine-delivery film that holds promise for improving the effectiveness of DNA vaccines. If such vaccines could be successfully delivered to humans, they could overcome not only the safety risks of using viruses to vaccinate against diseases such as HIV, but they would also be more stable, making it possible to ship and store them at room temperature.
This type of vaccine delivery would also eliminate the need to inject vaccines by syringe, says Darrell Irvine, an MIT professor of biological engineering and materials science and engineering. “You just apply the patch for a few minutes, take it off and it leaves behind these thin polymer films embedded in the skin,” he says. The researchers can control how much DNA gets delivered by tuning the number of polymer layers. They can also control the rate of delivery by altering how hydrophobic (water-fearing) the film is. DNA injected on its own is usually broken down very quickly, before the immune system can generate a memory response. When the DNA is released over time, the immune system has more time to interact with it, boosting the vaccine’s effectiveness.
The polymer film also includes an adjuvant — a molecule that helps to boost the immune response. In this case, the adjuvant consists of strands of RNA that resemble viral RNA, which provokes inflammation and recruits immune cells to the area.
The ability to provoke inflammation is one of the key advantages of the new delivery system, says Michele Kutzler, an assistant professor at Drexel University College of Medicine. Other benefits include targeting the wealth of immune cells in the skin, the use of a biodegradable delivery material, and the possibility of pain-free vaccine delivery, she says.
A working invisibility cloak that makes one object look like ghostly versions of another has been built in China. Conventional illusion cloaks rely on a two stage process. The first is a kind of invisibility stage which distorts incoming light to remove the scattering effect of the cloaked object, an apple for example. The second stage then distorts the scattered light to make it look as if it has been scattered off another object, a banana, for example. The result is that the apple ends up looking like a banana. But materials that can perform this two-stage process are too demanding to make with current techniques. So Tie Jun Cui and co have developed a single stage process that achieves a slightly different effect. Their idea is to do away with the first stage that makes the apple invisible. Instead, their device takes the light scattered from the apple and distorts it to look like something else such as a banana. The symmetry of the effect–light is scattered on both sides of the apple–mean that this approach produces two “ghost” bananas, one on each side of the apple. The technique does not remove the apple entirely but distorts it, making it appear much smaller. So the result is that the apple is changed into a much more complex picture that is significantly different from the original.
The big advantage of this approach is that it can be achieved now with existing technology. Tie Jun Cui and co first simulate the effect of their ghost cloak on a computer model. They then go on to build a working prototype using concentric cylinders of split ring resonators that operates in 2 dimensions. They say that the results of their tests on this device closely match the results of the simulation.
That’s an interesting advance. The ability to distort and camouflage objects is clearly useful. However, an important question is whether the distortion that this device offers is good enough for any practical applications. Tie Jun Cui and co mention “security enhancement” but just how effective this would be when the original object is still visible, albeit in shrunken form, is debatable.
The familiar button battery is the workhorse of small electronics. While it is likely to continue to power our existing watches and calculators for a little while, it has become the limiting factor for many key design points of these devices. Like a shipping container in a world of instant messaging, it has no future. One company, Imprint Energy, has assembled the total assault package which might sound the death knell — a rechargeable, flexible, customizable, and printable battery that is cheaper, safer and more powerful. The key technology developed by Imprint Energy is a polymer electrolyte that allows zinc-based batteries to be recharged. It prevents the formation of fingers which typically bridge across typical liquid electrolytes over time and make charging impossible. The flexible and customizable zinc anode, electrolyte, and metal oxide cathode of the battery are printed in the form of electrochemical inks. The printing process is similar to old-fashioned silk-screening where material is deposited in a pattern by squeezing it through a mesh over a template. While this screen printing is different from what we tend to think of nowadays as3D printing, the use of inkjets and other technologies are driving new convergent, hybrid techniques.
Researchers from North Carolina State University have created conductive wires that can be stretched up to eight times their original length while still functioning. The wires can be used for everything from headphones to phone chargers, and hold potential for use in electronic textiles. The fibers consist of a liquid metal alloy, eutectic gallium indium (EGaIn), injected into the core of stretchable hollow fibers composed of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) resin. The hollow fibers are easy to mass-produce with controlled size by using commercially available melt processing methods. The fibers are similar to conventional metallic wires (metal core, surrounded by polymeric insulation), but can be stretched orders of magnitude further while retaining electrical conductivity. Mechanical measurements with and without the liquid metal inside the fibers show the liquid core has a negligible impact on the mechanical properties of the fibers, which is in contrast to most conductive composite fibers. The fibers also maintain the same tactile properties with and without the metal because the conductive elements are confined to the core of the fiber. As expected, electrical measurements show that the fibers increase resistance as the fiber elongates and the cross sectional area narrows. Fibers with large diameters (~600 [micrometers]) change from a triangular to a more circular cross-section during stretching, which has the appeal of lowering the resistance below that predicted by theory. The ability of the liquid metal to flow during the elongation of the fibers results in electrical continuity up to 1000% strain and metallic conductivity (~3×10-5 [Omega] cm) up to 700% strain. As a demonstration of their utility, the ultrastretchable fibers were used as the wires for stretchable earphones and a stretchable battery charger. To make the wires, researchers start with a thin tube made of an extremely elastic polymer and then fill the tube with a liquid metal alloy of gallium and indium, which is an efficient conductor of electricity. The tube, filled with liquid metal, can be stretched many times its original length. “Previous efforts to create stretchable wires focus on embedding metals or other electrical conductors in elastic polymers, but that creates a trade-off,” says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State. “Increasing the amount of metal improves the conductivity of the composite, but diminishes its elasticity,” Dickey says. “Our approach keeps the materials separate, so you have maximum conductivity without impairing elasticity. In short, our wires are orders of magnitude more stretchable than the most conductive wires, and at least an order of magnitude more conductive than the most stretchable wires currently in the literature.”
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