Creating new opportunities from nanoscale ma…

Creating new opportunities from nanoscale materials

A hundred years ago, “2d” meant a two-penny, or 1-inch, nail. Today, “2-D” encompasses a broad range of atomically thin flat materials, many with exotic properties not found in the bulk equivalents of the same materials, with graphene—the single-atom-thick form of carbon—perhaps the most prominent. While many researchers at MIT and elsewhere are exploring two-dimensional materials and their special properties, Frances M. Ross, the Ellen Swallow Richards Professor in Materials Science and Engineering, is interested in what happens when these 2-D materials and ordinary 3-D materials come together.

“We’re interested in the interface between a 2-D material and a 3-D material because every 2-D material that you want to use in an application, such as an electronic device, still has to talk to the outside world, which is three-dimensional,” Ross says.

“We’re at an interesting time because there are immense developments in instrumentation for electron microscopy, and there is great interest in materials with very precisely controlled structures and properties, and these two things cross in a fascinating way,” says Ross.

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New low-cost thermoelectric material works at room temperature

Material could be used to cool electronic devices, overheated vehicles

Has your steering wheel been too hot to touch this summer? A new thermoelectric material reported in the journal Science could offer relief.

The widespread adoption of thermoelectric devices that can directly convert electricity into thermal energy for cooling and heating has been hindered, in part, by the lack of materials that are both inexpensive and highly efficient at room temperature.

Now researchers from the University of Houston and the Massachusetts Institute of Technology have reported the discovery of a new material that works efficiently at room temperature while requiring almost no costly tellurium, a major component of the current state-of-the-art material.

The work, described in a paper published online by ScienceThursday, July 18, has potential applications for keeping electronic devices, vehicles and other components from overheating, said Zhifeng Ren, corresponding author on the work and director of the Texas Center for Superconductivity at UH, where he is also M.D. Anderson Professor of Physics.

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New Kind of Solar Cell Opens the Door for Su…

New Kind of Solar Cell Opens the Door for Surpassing Efficiency Limit 

In any conventional silicon-based solar cell, there is an absolute limit on overall efficiency, based partly on the fact that each photon of light can only knock loose a single electron, even if that photon carried twice the energy needed to do so. But now, researchers have demonstrated a method for getting high-energy photons striking silicon to kick out two electrons instead of one, opening the door for a new kind of solar cell with greater efficiency than was thought possible.

While conventional silicon cells have an absolute theoretical maximum efficiency of about 29.1 percent conversion of solar energy, the new approach, developed over the last several years by researchers at MIT and elsewhere, could bust through that limit, potentially adding several percentage points to that maximum output. The results are described today in the journal Nature, in a paper by graduate student Markus Einzinger, professor of chemistry Moungi Bawendi, professor of electrical engineering and computer science Marc Baldo, and eight others at MIT and at Princeton University.

The basic concept behind this new technology has been known for decades, and the first demonstration that the principle could work was carried out by some members of this team six years ago. But actually translating the method into a full, operational silicon solar cell took years of hard work, Baldo says.

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An atomic-scale erector set

An atomic-scale erector set

To predict building damage, Kostas Keremidis of the MIT Concrete Sustainability Hub is modeling structures as ensembles of atoms.

To design buildings that can withstand the largest of storms, Kostas Keremidis, a PhD candidate at the MIT Concrete Sustainability Hub, is using research at the smallest scale — that of the atom.

His approach, which derives partially from materials science, models a building as a collection of points that interact through forces like those found at the atomic scale.

“When you look at a building, it is actually a series of connections between columns, windows, doors, and so on,” says Keremidis. “Our new framework looks at how different building components connect together to form a building like atoms form a molecule — similar forces hold them together, both at the atomic and building scale.” The framework is called molecular dynamics-based structural modeling.

Eventually, Keremidis hopes it will provide developers and builders with a new way to readily predict building damage from disasters like hurricanes and earthquakes.

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Engineers 3D print flexible mesh for ankle and knee braces

Techniques could lead to personalized wearable and implantable devices

Hearing aids, dental crowns, and limb prosthetics are some of the medical devices that can now be digitally designed and customized for individual patients, thanks to 3-D printing. However, these devices are typically designed to replace or support bones and other rigid parts of the body, and are often printed from solid, relatively inflexible material.

Now MIT engineers have designed pliable, 3-D-printed mesh materials whose flexibility and toughness they can tune to emulate and support softer tissues such as muscles and tendons. They can tailor the intricate structures in each mesh, and they envision the tough yet stretchy fabric-like material being used as personalized, wearable supports, including ankle or knee braces, and even implantable devices, such as hernia meshes, that better match to a person’s body.

As a demonstration, the team printed a flexible mesh for use in an ankle brace. They tailored the mesh’s structure to prevent the ankle from turning inward – a common cause of injury – while allowing the joint to move freely in other directions. The researchers also fabricated a knee brace design that could conform to the knee even as it bends. And, they produced a glove with a 3-D-printed mesh sewn into its top surface, which conforms to a wearer’s knuckles, providing resistance against involuntary clenching that can occur following a stroke.

“This work is new in that it focuses on the mechanical properties and geometries required to support soft tissues,” says Sebastian Pattinson, who conducted the research as a postdoc at MIT.

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Researchers solve mystery of how gas bubbles…

Researchers solve mystery of how gas bubbles form in liquid

The formation of air bubbles in a liquid appears very similar to its inverse process, the formation of liquid droplets from, say, a dripping water faucet. But the physics involved is actually quite different, and while those water droplets are uniform in their size and spacing, bubble formation is typically a much more random process.

Now, a study by researchers at MIT and Princeton University shows that under certain conditions, bubbles can also be coaxed to form spheres as perfectly matched as droplets.

The new findings could have implications for the development of microfluidic devices for biomedical research and for understanding the way natural gas interacts with petroleum in the tiny pore spaces of underground rock formations, the researchers say. The findings are published today in the journal PNAS, in a paper by MIT graduate Amir Pahlavan Ph.D. ‘18, Professor Howard Stone of Princeton, MIT School of Engineering Professor of Teaching Innovation Gareth McKinley, and MIT Professor Ruben Juanes.

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Pantry ingredients can help grow carbon nano…

Pantry ingredients can help grow carbon nanotubes

Baking soda, table salt, and detergent are surprisingly effective ingredients for cooking up carbon nanotubes, researchers at MIT have found.

In a study published this week in the journal Angewandte Chemie, the team reports that sodium-containing compounds found in common household ingredients are able to catalyze the growth of carbon nanotubes, or CNTs, at much lower temperatures than traditional catalysts require.

The researchers say that sodium may make it possible for carbon nanotubes to be grown on a host of lower-temperature materials, such as polymers, which normally melt under the high temperaturesneeded for traditional CNT growth.

“In aerospace composites, there are a lot of polymers that hold carbon fibers together, and now we may be able to directly grow CNTs on polymer materials, to make stronger, tougher, stiffer composites,” says Richard Li, the study’s lead author and a graduate student in MIT’s Department of Aeronautics and Astronautics. “Using sodium as a catalyst really unlocks the kinds of surfaces you can grow nanotubes on.”

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‘Metasurfaces’ that manipulate l…

‘Metasurfaces’ that manipulate light at tiny scales could find uses in consumer technology

Most of us know optical lenses as curved, transparent pieces of plastic or glass, designed to focus light for microscopes, spectacles, cameras, and more. For the most part, a lens’ curved shape has not changed much since it was invented many centuries ago.

In the last decade, however, engineers have created flat, ultrathin materials called “metasurfaces” that can perform tricks of light far beyond what traditional curved lenses can do. Engineers etch individual features, hundreds of times smaller than the width of a single human hair, onto these metasurfaces to create patterns that enable the surface as a whole to scatter light very precisely. But the challenge is to know exactly what pattern is needed to produce a desired optical effect.

That’s where MIT mathematicians have come up with a solution. In a study published this week in Optics Express, a team reports a new computational technique that quickly determines the ideal makeup and arrangement of millions of individual, microscopic features on a metasurface, to generate a flat lens that manipulates light in a specified way.

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New surface treatment could improve refrigerat…

New surface treatment could improve refrigeration efficiency: A slippery surface for liquids with very low surface tension promotes droplet formation, facilitating heat transfer

Unlike water, liquid refrigerants and other fluids that have a low surface tension tend to spread quickly into a sheet when they come into contact with a surface. But for many industrial processes it would be better if the fluids formed droplets, which could roll or fall off the surface and carry heat away with them.

[…]

Now, researchers at MIT have made significant progress in promoting droplet formation and shedding in such fluids. This approach could lead to efficiency improvements in many large-scale industrial processes including refrigeration, thus saving energy and reducing greenhouse gas emissions.

The new findings are described in the journal Joule, in a paper by recent graduate and postdoc Karim Khalil PhD ‘18, professor of mechanical engineering Kripa Varanasi, professor of chemical engineering and Associate Provost Karen Gleason, and four others.

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New polymer films conduct heat instead of tr…

New polymer films conduct heat instead of trapping it

Material may replace many metals as lightweight, flexible heat dissipators in cars, refrigerators, and electronics

Polymers are usually the go-to material for thermal insulation. Think of a silicone oven mitt, or a Styrofoam coffee cup, both manufactured from polymer materials that are excellent at trapping heat.

Now MIT engineers have flipped the picture of the standard polymer insulator, by fabricating thin polymer films that conduct heat – an ability normally associated with metals. In experiments, they found the films, which are thinner than plastic wrap, conduct heat better than many metals, including steel and ceramic.

The team’s results, published in the journal Nature Communications, may spur the development of polymer insulators as lightweight, flexible, and corrosion-resistant alternatives to traditional metal heat conductors, for applications ranging from heat dissipating materials in laptops and cellphones, to cooling elements in cars and refrigerators.

“We think this result is a step to stimulate the field,” says Gang Chen, the Carl Richard Soderberg Professor of Power Engineering at MIT, and a senior co-author on the paper. “Our bigger vision is, these properties of polymers can create new applications and perhaps new industries, and may replace metals as heat exchangers.”

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