How about a metal that won’t sink in water no matter what? Could this lead to an unsinkable ship?

A metallic structure etched by lasers, right, floats to the top on the water’s surface in professor Chunlei Guo’s lab. (University of Rochester photo / J. Adam Fenster)

University of Rochester researchers, inspired by diving bell spiders and rafts of fire ants, have created a metallic structure that is so water repellent, it refuses to sink—no matter how often it is forced into water or how much it is damaged or punctured.

Could this lead to an unsinkable ship? A wearable flotation device that will still float after being punctured? Electronic monitoring devices that can survive in long term in the ocean?

All of the above, says Chunlei Guo, professor of optics and physics, whose lab describes the structure in ACS Applied Materials and Interfaces.

The structure uses a groundbreaking technique the lab developed for using femtosecond bursts of lasers to “etch” the surfaces of metals with intricate micro- and nanoscale patterns that trap air and make the surfaces superhydrophobic, or water repellent.

The researchers found, however, that after being immersed in water for long periods of time, the surfaces may start to lose their hydrophobic properties.

Enter the spiders and fire ants, which can survive long periods under or on the surface of water. How? By trapping air in an enclosed area. Argyroneta aquatic spiders, for example, create an underwater dome-shaped web—a so-called diving bell— that they fill with air carried from the surface between their super-hydrophobic legs and abdomens. Similarly, fire ants can form a raft by trapping air among their superhydrophobic bodies.

“That was a very interesting inspiration,” Guo says. As the researchers note in the paper: “The key insight is that multifaceted superhydrophobic (SH) surfaces can trap a large air volume, which points towards the possibility of using SH surfaces to create buoyant devices.”

Guo’s lab created a structure in which the treated surfaces on two parallel aluminum plates face inward, not outward, so they are enclosed and free from external wear and abrasion. The surfaces are separated by just the right distance to trap and hold enough air to keep the structure floating—in essence creating a waterproof compartment. The superhydrophobic surfaces will keep water from entering the compartment even when the structure is forced to submerge in water.

Even after being forced to submerge for two months, the structures immediately bounced back to the surface after the load was released, Guo says. The structures also retained this ability even after being punctured multiple times, because air remains trapped in remaining parts of the compartment or adjoining structures.

Though the team used aluminum for this project, the “etching process “could be used for literally any metals, or other materials,” Guo says.

When the Guo lab first demonstrated the etching technique, it took an hour to pattern a one-inch-by-one-inch area of surface. Now, by using lasers seven times as powerful, and faster scanning, the lab has speeded up the process, making it more feasible for scaling up for commercial applications.

Coauthors include lead author Zhibing Zhan, Mohamed ElKabbash, Jihua Zhang, and Subhash Singh, all PhD candidates or postdoctoral fellows in Guo’s lab, and Jinluo Cheng, associate professor at the Changchun Institute of Optics, Fine Mechanics, and Physics in China.

Learn more: Spiders and ants inspire metal that won’t sink

 

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New materials building blocks called bundlemers could usher in a new era of materials discovery

“These are tools for anybody to use, whether you’re a chemist, engineer, or physicist,” said Darrin Pochan (right), chair of the Department of Materials Science and Engineering at UD. “It’s hard to think of an equivalent material or experimental tool people use widely. It’s like a toolbox for anybody to design future things.”

New polymer units created by UD, Penn researchers could enable materials breakthroughs

From tires to clothes to shampoo, many ubiquitous products are made with polymers, large chain-like molecules made of smaller subunits called monomers, bonded together. Now, a team of researchers from the University of Delaware and the University of Pennsylvania, with primary support from the U.S. Department of Energy Biomolecular Materials Program, has created a new fundamental unit of polymers that could usher in a new era of materials discovery.

The researchers designed and created rigid, self-assembling, customizable polymer chains by linking together new building blocks called bundlemers — a term coined at UD. They recently described their work in the journal Nature.

To create bundlemers, the team assembles four individual peptides, themselves short chains of amino acids, into nanoscopic cylinders. The bundlemer cylinders are then linked together, end-to-end, through a highly efficient and controlled series of chemical reactions known as “click” chemistry. The resulting polymer chains are rigid, rod-like molecules that are based in biology yet do not exist in nature. Bundlemer chains can then be modified with components such as synthetic polymers or inorganic nanoparticles to create new hybrid nanomaterials.

“There’s a basic premise in materials that if you can control function and structure, then you can essentially build anything,” said Chris Kloxin, study author and assistant professor of materials science and engineering and chemical and biomolecular engineering at UD. “We have a very well-defined structural unit, this bundlemer, upon which we have the ability to add chemical functionality at any location.”

Because of their rigidity and customizability, bundlemers could be used to design new materials with a wide range of applications, from high-performance fibers to single-use plastics to biologics, medicines that employ biological components instead of traditional chemistries. Biopharmaceutical research and development is a growing area of expertise at UD, home to the National Institute of Innovation in Biopharmaceutical Manufacturing (NIIMBL).

The rigidity of bundlemers could also make these materials useful as substitutes for famously strong materials such as the steel in bridges, the silk in parachutes or the Kevlar in bulletproof vests.

Practically every day, co-author Darrin Pochan, chair of the Department of Materials Science and Engineering at UD, and Kloxin come up with a new application to pursue — enough to keep them and their students busy for years.

“Our idea is that these bundlemers truly are building blocks in every sense of the word,” said Pochan. “We are going to build many, many materials and technologies out of these building blocks.”

The team has applied for one patent and plans to file more.

The origin of bundlemers

Pochan and co-author Jeffery Saven, professor of chemistry at Penn, have collaborated since 2012, when they received a National Science Foundation DMREF grant to study designer materials. Kristi Kiick, Blue and Gold Distinguished Professor of Materials Science and Engineering, was also a collaborator on that project.

Saven’s computational chemistry group designs and models specific peptide sequences to identify promising candidates for synthesis and characterization. “Our group is involved in designing and identifying what to make, then modelling these systems to try to understand their stability,” Saven said about his group’s role in the collaboration.

Saven collaborates on new molecule designs with Pochan and now Kloxin, who joined the collaboration later, where they discuss the pros and cons of different peptide sequences and how to best create a new material with a specific property. Then, at UD, Pochan and Kloxin make the materials.

“It’s good to have feedback on important features to include in the calculations,” said Saven about the importance of iterative discussions between groups at UD and Penn.

Said Pochan: “We computationally design and then experimentally create the molecules to do the assembly into the bundlemer building blocks. We are not limited to nature’s toolbox.”

Still, despite careful planning, the initial experimental results surprised Pochan and Kloxin — in a good way. When they first saw measurements of the bundlemer chain stiffness, they assumed that something was wrong. Usually polymer chains are loose and flexible like spaghetti, but polymers created from bundlemers are more like long, thin, sturdy rods.

“The rigidity was quite surprising and stunning,” said Pochan. It wasn’t a mistake. Additional testing revealed that bundlemers have a much higher stiffness by weight than almost any other polymers, such as synthetic polymers and DNA.

After synthesizing bundlemers, the research team characterized the materials using transmission electron microscopy and cryogenic transmission electron microscopy in the Keck Center for Advanced Microscopy and Microanalysis. They also confirmed the size and structure of the bundlemers through small-angle neutron scattering experiments at the National Institute of Standards and Technology’s Center for Neutron Research, which has a cooperative agreement with UD for the Center for Neutron Science.

Jeff Caplan, confocal microscopy expert and director of BioImaging at the Delaware Biotechnology Institute, performed Stochastic Optical Reconstruction Microscopy (STORM) Imaging to visualize tiny segments within the bundlemers. Caplan is a co-author on the Nature paper.

This project wouldn’t have been possible without the complementary expertise of the principal investigators. Saven excels in computations and theory. Kloxin excels in polymer chemistry. Pochan excels in materials synthesis and characterization.

“We have plenty of overlap with our expertise, but the point is that without one of us, none of this would have happened,” said Pochan. “Without facilities, such as UD’s Keck Microscopy Lab, the BioImaging Center at the Delaware Biotechnology Institute, and our relationship with NIST and the Center for Neutron Research, this kind of work would not happen.”

The future of bundlemers

Next, the team aims to make bundlemers more accessible, easier to synthesize, and scalable.

Scientists around the world could use bundlemers to address a wide variety of grand challenges in engineering.

“These are tools for anybody to use, whether you’re a chemist, engineer, or physicist,” said Pochan. “It’s hard to think of an equivalent material or experimental tool people use widely. It’s like a toolbox for anybody to design future things.”

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New polymer films may replace many metals as lightweight, flexible heat dissipators in cars, refrigerators, and electronics

By mixing polymer powder in solution to generate a film that they then stretched, MIT researchers have changed polyethylene’s microstructure, from spaghetti-like clumps of molecular chains (left), to straighter strands (right), allowing heat to conduct through the polymer, better than most metals.
Image courtesy of the researchers

New polymer films conduct heat instead of trapping it

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 ceramics and many metals, including steel.

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.”

Chen’s co-authors include lead author Yanfei Xu, along with Daniel Kraemer, Bai Song, Jiawei Zhou, James Loomis, Jianjian Wang, Mingda Li, Hadi Ghasemi, Xiaopeng Huang, and Xiaobo Li from MIT, and Zhang Jiang of Argonne National Laboratory.

In 2010, the team reported success in fabricating thin fibers of polyethylene that were 300 times more thermally conductive than normal polyethylene, and about as conductive as most metals. Their results, published in Nature Nanotechnology, drew the attention of various industries, including manufacturers of heat exchangers, computer core processors, and even race cars.

It soon became clear that, in order for polymer conductors to work for any of these applications, the materials would have to be scaled up from ultrathin fibers (a single fiber measured one-hundredth of the diameter of a human hair) to more manageable films.

“At that time we said, rather than a single fiber, we can try to make a sheet,” Chen says. “It turns out it was a very arduous process.”

The researchers not only had to come up with a way to fabricate heat-conducting sheets of polymer, but they also had to custom-build an apparatus to test the material’s heat conduction, as well as develop computer codes to analyze images of the material’s microscopic structures.

In the end, the team was able to fabricate thin films of conducting polymer, starting with a commercial polyethylene powder. Normally, the microscopic structure of polyethylene and most polymers resembles a spaghetti-like tangle of molecular chains. Heat has a difficult time flowing through this jumbled mess, which explains a polymer’s intrinsic insulating properties.

Xu and her colleagues looked for ways to untangle polyethylene’s molecular knots, to form parallel chains along which heat can better conduct. To do this, they dissolved polyethylene powder in a solution that prompted the coiled chains to expand and untangle. A custom-built flow system further untangled the molecular chains, and spit out the solution onto a liquid-nitrogen-cooled plate to form a thick film, which was then placed on a roll-to-roll drawing machine that heated and stretched the film until it was thinner than plastic wrap.

The team then built an apparatus to test the film’s heat conduction. While most polymers conduct heat at around 0.1 to 0.5 watts per meter per kelvin, Xu found the new polyethylene film measured around 60 watts per meter per kelvin. (Diamond, the best heat-conducting material, comes in at around 2,000 watts per meter per kelvin, while ceramic measures about 30, and steel, around  15.) As it turns out, the team’s film is two orders of magnitude more thermally conductive than most polymers, and also more conductive than steel and ceramics.

To understand why these engineered polyethylene films have such an unusually high thermal conductivity, the team conducted X-ray scattering experiments at the U.S. Department of Energy’s Advanced Photon Source (APS) at the Argonne National Laboratory.

“These experiments, at one of the world’s most bright synchrotron X-ray facilities, allow us to see the nanoscopic details within the individual fibers that make up the  stretched film,” Jiang says.

By imaging the ultrathin films, the researchers observed that the films exhibiting better heat conduction consisted of nanofibers with less randomly coiled chains, versus those in common polymers, which resemble tangled spaghetti. Their observations could help researchers engineer polymer microstructures to efficiently conduct heat.

“This dream work came true in the end,” Xu says.

Going forward, the researchers are looking for ways to make even better polymer heat conductors, by both adjusting the fabrication process and experimenting with different types of polymers.

Zhou points out that the team’s polyethylene film conducts heat only along the length of the fibers that make up the film. Such a unidirectional heat conductor could be useful in carrying heat away in a specified direction, inside devices such as laptops and other electronics. But ideally, he says the film should dissipate heat more effectively in any direction.

“If we have an isotropic polymer with good heat conductivity, then we can easily blend this material into a composite, and we can potentially replace a lot of conductive materials,” Zhou says. “So we’re looking into better heat conduction in all three dimensions.”

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Revolutionary insulator-like material also conducts electricity

The new material, grown in a chamber like this, could lay the groundwork for ultrafast electronic devices, such as the cellphones and computers of the future. UW–MADISON PHOTO BY SAM MILLION-WEAVER

University of Wisconsin–Madison researchers have made a material that can transition from an electricity-transmitting metal to a nonconducting insulating material without changing its atomic structure.

“This is quite an exciting discovery,” says Chang-Beom Eom, professor of materials science and engineering. “We’ve found a new method of electronic switching.”

The new material could lay the groundwork for ultrafast electronic devices, such as the cellphones and computers of the future. Eom and his international team of collaborators published details of their advance today (Nov. 29, 2018) in the journal Science.

Metals like copper or silver conduct electricity, whereas insulators like rubber or glass do not allow current to flow. Some materials, however, can transition from insulating to conducting and back again.

This transition usually means that the arrangement of a material’s atoms and its conducting electrons must change in a coordinated way, but the atomic transition typically proceeds much more slowly than the smaller, lighter electrons that conduct electricity.

A material that can switch to conducting electricity like a metal without moving its atoms could dramatically advance switching speeds of advanced devices, says Eom.

“The metal-to-insulator transition is very important for switches and for logic devices with a one or a zero state,” he says. “We have the potential to use this concept to make very fast switches.”

In their research, Eom and his collaborators answered a fundamental question that has bothered scientists for years: Can the electronic and structural transition be decoupled — essentially, can the quickly changing electrons break out on their own and leave the atoms behind?

They used a material called vanadium dioxide, which is a metal when it’s heated and an insulator when it’s at room temperature. At high temperatures, the atoms that make up vanadium dioxide are arranged in a regularly repeating pattern that scientists refer to as the rutile phase. When vanadium dioxide cools down to become an insulator, its atoms adopt a different pattern, called monoclinic.

No naturally occurring substances conduct electricity when their atoms are in the monoclinic conformation. And it takes time for the atoms to rearrange when a material reaches the insulator-to-metal transition temperature.

Crucially, vanadium dioxide transitions between a metal and an insulator at different temperatures depending upon the amount of oxygen present in the material. The researchers leveraged that fact to create two thin layers of vanadium dioxide — one with a slightly lower transition temperature than the other — sandwiched on top of each other, with a sharp interface between.

When they heated the thin vanadium dioxide sandwich, one layer made the structural switch to become a metal. Atoms in the other layer remained locked into the insulating monoclinic phase. Surprisingly, however, that part of the material conducted electricity.

The new material could lay the groundwork for ultrafast electronic devices, such as the cellphones and computers of the future.

Most importantly, the material remained stable and retained its unique characteristics.

Although other research groups have attempted to create electrically conductive insulators, those materials lost their properties almost instantly — persisting for mere femtoseconds, or a few thousandths of one trillionth of a second.

The Eom team’s material, however, is here to stay.

“We were able to stabilize it, making it useful for real devices,” says Eom.

Key to their approach was the dual-layer, sandwich structure. Each layer was so thin that the interface between the two materials dominated how the entire stack behaved. It’s a notion that Eom and colleagues plan to pursue further.

“Designing interfaces could open up new materials,” says Eom.

Learn more: Switching identities: Revolutionary insulator-like material also conducts electricity

 

 

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Using artificial intelligence to design billions of possible new materials

At the University of Missouri, researchers in the College of Engineering are applying one of the first uses of deep learning — the technology computers use to intelligently perform tasks such as recognizing language and driving autonomous vehicles — to the field of materials science

A team of MU researchers are applying one of the first uses of artificial intelligence principles to the field of materials science

Discovering how atoms — such as a single layer of carbon atoms found in graphene, one of the world’s strongest materials — work to create a solid material is currently a major research topic in the field of materials science, or the design and discovery of new materials. At the University of Missouri, researchers in the College of Engineering are applying one of the first uses of deep learning — the technology computers use to intelligently perform tasks such as recognizing language and driving autonomous vehicles — to the field of materials science.

“You can train a computer to do what it would take many years for people to otherwise do,” said Yuan Dong, a research assistant professor of mechanical and aerospace engineering and lead researcher on the study. “This is a good starting point.”

Dong worked with Jian Lin, an assistant professor of mechanical and aerospace engineering, to determine if there was a way to predict the billions of possibilities of material structures created when certain carbon atoms in graphene are replaced with non-carbon atoms.

“If you put atoms in certain configurations, the material will behave differently,” Lin said. “Structures determine the properties. How can you predict these properties without doing experiments? That’s where computational principles come in.”

Lin and Dong partnered with Jianlin Cheng, a William and Nancy Thompson Professor of Electrical Engineering and Computer Science at MU, to input a few thousand known combinations of graphene structures and their properties into deep learning models. From there, it took about two days for the high-performance computer to learn and predict the properties of the billions of other possible structures of graphene without having to test each one separately.

Researchers envision future uses of this artificial intelligence assistive technology in designing many different graphene related or other two-dimensional materials. These materials could be applied to the construction of LED televisions, touch screens, smartphones, solar cells, missiles and explosive devices.

“Give an intelligent computer system any design, and it can predict the properties,” Cheng said. “This trend is emerging in the material science field. It’s a great example of applying artificial intelligence to change the standard process of material design in this field.”

Learn more: Teaching computers to intelligently design ‘billions’ of possible materials

 

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