Thursday, 19 April 2018 10:54

A graphene roll-out

Scalable manufacturing process spools out strips of graphene for use in ultrathin membranes.
MIT Graphene Roll 01
A new manufacturing process produces strips of graphene, at large scale, for use in membrane technologies and other applications. Image, Christine Daniloff, MIT

MIT engineers have developed a continuous manufacturing process that produces long strips of high-quality graphene.

The team’s results are the first demonstration of an industrial, scalable method for manufacturing high-quality graphene that is tailored for use in membranes that filter a variety of molecules, including salts, larger ions, proteins, or nanoparticles. Such membranes should be useful for desalination, biological separation, and other applications.

“For several years, researchers have thought of graphene as a potential route to ultrathin membranes,” says John Hart, associate professor of mechanical engineering and director of the Laboratory for Manufacturing and Productivity at MIT. “We believe this is the first study that has tailored the manufacturing of graphene toward membrane applications, which require the graphene to be seamless, cover the substrate fully, and be of high quality.”

Hart is the senior author on the paper, which appears online in the journal Applied Materials and Interfaces. The study includes first author Piran Kidambi, a former MIT postdoc who is now an assistant professor at Vanderbilt University; MIT graduate students Dhanushkodi Mariappan and Nicholas Dee; Sui Zhang of the National University of Singapore; Andrey Vyatskikh, a former student at the Skolkovo Institute of Science and Technology who is now at Caltech; and Rohit Karnik, an associate professor of mechanical engineering at MIT.

Growing graphene

For many researchers, graphene is ideal for use in filtration membranes. A single sheet of graphene resembles atomically thin chicken wire and is composed of carbon atoms joined in a pattern that makes the material extremely tough and impervious to even the smallest atom, helium.

Researchers, including Karnik’s group, have developed techniques to fabricate graphene membranes and precisely riddle them with tiny holes, or nanopores, the size of which can be tailored to filter out specific molecules. For the most part, scientists synthesize graphene through a process called chemical vapor deposition, in which they first heat a sample of copper foil and then deposit onto it a combination of carbon and other gases.

Graphene-based membranes have mostly been made in small batches in the laboratory, where researchers can carefully control the material’s growth conditions. However, Hart and his colleagues believe that if graphene membranes are ever to be used commercially they will have to be produced in large quantities, at high rates, and with reliable performance.

“We know that for industrialization, it would need to be a continuous process,” Hart says. “You would never be able to make enough by making just pieces. And membranes that are used commercially need to be fairly big ­— some so big that you would have to send a poster-wide sheet of foil into a furnace to make a membrane.”

A factory roll-out

The researchers set out to build an end-to-end, start-to-finish manufacturing process to make membrane-quality graphene.

The team’s setup combines a roll-to-roll approach — a common industrial approach for continuous processing of thin foils — with the common graphene-fabrication technique of chemical vapor deposition, to manufacture high-quality graphene in large quantities and at a high rate. The system consists of two spools, connected by a conveyor belt that runs through a small furnace. The first spool unfurls a long strip of copper foil, less than 1 centimeter wide. When it enters the furnace, the foil is fed through first one tube and then another, in a “split-zone” design.

While the foil rolls through the first tube, it heats up to a certain ideal temperature, at which point it is ready to roll through the second tube, where the scientists pump in a specified ratio of methane and hydrogen gas, which are deposited onto the heated foil to produce graphene.

“Graphene starts forming in little islands, and then those islands grow together to form a continuous sheet,” Hart says. “By the time it’s out of the oven, the graphene should be fully covering the foil in one layer, kind of like a continuous bed of pizza.”

As the graphene exits the furnace, it’s rolled onto the second spool. The researchers found that they were able to feed the foil continuously through the system, producing high-quality graphene at a rate of 5 centimers per minute. Their longest run lasted almost four hours, during which they produced about 10 meters of continuous graphene.

“If this were in a factory, it would be running 24-7,” Hart says. “You would have big spools of foil feeding through, like a printing press.”

Flexible design

Once the researchers produced graphene using their roll-to-roll method, they unwound the foil from the second spool and cut small samples out. They cast the samples with a polymer mesh, or support, using a method developed by scientists at Harvard University, and subsequently etched away the underlying copper.

“If you don’t support graphene adequately, it will just curl up on itself,” Kidambi says. “So you etch copper out from underneath and have graphene directly supported by a porous polymer — which is basically a membrane.”

MIT Graphene Roll 02
The process consists of a “roll-to-roll” system that spools out a ribbon of copper foil from one end, which is fed through a furnace. Methane and hydrogen gas are deposited onto the foil to form graphene, which then exits the furnace and is rolled up for further development. Courtesy of the researchers

The polymer covering contains holes that are larger than graphene’s pores, which Hart says act as microscopic “drumheads,” keeping the graphene sturdy and its tiny pores open.

The researchers performed diffusion tests with the graphene membranes, flowing a solution of water, salts, and other molecules across each membrane. They found that overall, the membranes were able to withstand the flow while filtering out molecules. Their performance was comparable to graphene membranes made using conventional, small-batch approaches.

The team also ran the process at different speeds, with different ratios of methane and hydrogen gas, and characterized the quality of the resulting graphene after each run. They drew up plots to show the relationship between graphene’s quality and the speed and gas ratios of the manufacturing process. Kidambi says that if other designers can build similar setups, they can use the team’s plots to identify the settings they would need to produce a certain quality of graphene.

“The system gives you a great degree of flexibility in terms of what you’d like to tune graphene for, all the way from electronic to membrane applications,” Kidambi says.

Looking forward, Hart says he would like to find ways to include polymer casting and other steps that currently are performed by hand, in the roll-to-roll system.

“In the end-to-end process, we would need to integrate more operations into the manufacturing line,” Hart says. “For now, we’ve demonstrated that this process can be scaled up, and we hope this increases confidence and interest in graphene-based membrane technologies, and provides a pathway to commercialization.”

– Jennifer Chu | MIT News Office
April 17, 2018

 

 

Faculty members recognized for excellence via a diverse array of honors, grants, and prizes over the last quarter. 
MIT SOE Awards Q2 Paquette 2018 Web
Image, Lillie Paquette/School of Engineering.

Members of the MIT engineering faculty receive many awards in recognition of their scholarship, service, and overall excellence. Every quarter, the School of Engineering publicly recognizes their achievements by highlighting the honors, prizes, and medals won by faculty working in our academic departments, labs, and centers.

The following awards were given from January through March, 2018. Submissions for future listings are welcome at any time.

Lallit Anand, Department of Mechanical Engineering, was elected to the National Academy of Engineering on Feb. 7.

Polina Anikeeva, Department of Materials Science and Engineering, was awarded the Vilcek Prize on Feb. 1.

Regina Barzilay, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was named an Association for Computational Linguistics Fellow on Feb. 20.

János Beér and William H. Green Jr., Department of Chemical Engineering, were named Inaugural Fellows of The Combustion Institute on Feb. 22.

Angela Belcher, Department of Materials Science and Engineering and the Department of Biological Engineering, was elected to the National Academy of Engineering on Feb. 7.

Michael Birnbaum, Department of Biological Engineering and the Koch Institute for Integrative Cancer Research, was awarded a Jimmy V Foundation Scholar Grant on Feb. 25.

Tamara Broderick, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the Army Research Office Young Investigator Program Award on Jan. 23; she was also awarded a Sloan Research Fellowship on Feb. 15 and was honored with a National Science Foundation CAREER Award on March 15.

W. Craig Carter, Department of Materials Science and Engineering, was awarded a J-WEL Grant on Feb. 1.

Arup K. Chakraborty, Institute for Medical Engineering and Science and the Department of Chemical Engineering, was awarded a Moore Fellowship at Caltech on Jan. 1.

Edward Crawley, Department of Aeronautics and Astronautics was inducted as a foreign member into the Russian Academy of Science on March 29.

Mark Drela, Department of Aeronautics and Astronautics, received the AIAA Reed Aeronautics Award on Feb. 21.

Elazer R. Edelman, Institute for Medical Engineering and Science, was honored with the Giulio Natta Medal in Chemical Engineering from the Department of Chemistry, Materials and Chemical Engineering "Giulio Natta" of Milan Polytechnic on Feb. 6; he also won the 2018 Distinguished Scientist Award from the American College of Cardiology.

Ahmed Ghoniem, Department of Mechanical Engineering, was named a fellow of The Combustion Institute on Feb. 23.

Shafi Goldwasser, Silvio Micali, and Ron Rivest, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, were honored with BBVA Foundation Frontiers of Knowledge Awards in the Information and Communication Technologies Category on Jan. 17.

Stephen Graves, Department of Mechanical Engineering and the Sloan School of Management, was elected to the National Academy of Engineering on Feb. 7.

Paula Hammond, Department of Chemical Engineering and the Koch Institute for Integrative Cancer Research, won the American Chemical Society Award in Applied Polymer Science on Jan. 8.

Daniel Jackson, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the MIT Martin Luther King Jr. Leadership Award on Feb. 8.

Stefanie Jegelka, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was awarded a Sloan Research Fellowship on Feb. 15.

Heather Kulik, Department of Chemical Engineering, won an Office of Naval Research Young Investigator Award on Feb. 21.

John Lienhard, Department of Mechanical Engineering, was named one of the Top 25 Global Water Leaders on Jan. 10.

Barbara Liskov, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the IEEE Computer Society 2018 Computer Pioneer Award on Feb. 16.

Luqiao Liu, Department of Electrical Engineering and Computer Science, won the William L. McMillan Award on March 27; he was also honored with the 2017 Young Scientist Prize in the field of Magnetism by the International Union of Pure and Applied Physics on Feb. 12.

Wenjie Lu, Department of Electrical Engineering and Computer Science, was recognized by the Next Generation Workforce on Feb. 12.

Stefanie Mueller, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won an Outstanding Dissertation Award from the Association for Computing Machinery Special Interest Group on Computer-Human Interaction (ACM SIGCHI) on Feb. 15.

Dava J. Newman, Department of Aeronautics and Astronautics, was named a 2018 American Institute of Aeronautics and Astronautics Fellow on Feb. 1.

Pablo A. Parrilo, Department of Electrical Engineering and Computer Science, was named a 2018 Society of Industrial Applied Mathematics Fellow on March 29.

Bryan Reimer, Center for Transportation and Logistics, won the Autos2050 Driving Innovation Award on Jan. 10.

Ronald Rivest, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was inducted into the National Inventors Hall of Fame on Jan. 23.

Daniela Rus, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the Pioneer in Robotics and Automation Award from the IEEE Robotics and Automation Society on Jan. 24.

Noelle Selin, Institute for Data, Systems, and Society, was awarded a Hans Fischer Senior Fellowship on March 23.

Devavrat Shah, Department of Electrical Engineering and Computer Science and the Institute for Data, Systems, and Society won a Frank Quick Faculty Research Innovation Award on Feb. 20.

Julie Shah, Department of Aeronautics and Astronautics and the Computer Science and Artificial Intelligence Laboratory won the 2018 Robotics and Automation Society Early Career Award on March 23.

Alex K. Shalek, Institute for Medical Engineering and Science and the Department of Chemistry, was honored with a 2018 Sloan Research Fellowship on Feb. 15.

Yang Shao-Horn, Department of Mechanical Engineering and Materials Science and Engineering, was elected to the National Academy of Engineering on Feb. 7.

Cem Tasan, Department of Materials Science and Engineering, won the Young Investigator Award on Feb. 22.

Karen Willcox, Department of Aeronautics and Astronautics, was named a 2018 Society of Industrial Applied Mathematics Fellow on March 29.

Laurence R. Young, Department of Aeronautics and Astronautics and the Institute for Medical Engineering and Science, was awarded the 2018 de Florez Award for Flight Simulation from the American Institute of Aeronautics and Astronautics on Jan. 9.

Nickolai Zeldovich, Department of Electrical Engineering and Computer Science (EECS) and the Computer Science and Artificial Intelligence Laboratory, was awarded a Faculty Research Innovation Award from EECS on Feb. 20.

– School of Engineering | MIT News
April 3, 2018

 

Technique could prevent overheating of laptops, mobile phones, and other electronics.
MIT Polymer Conductor
Engineers at MIT have developed a polymer thermal conductor — a plastic material that, however counterintuitively, works as a heat conductor, dissipating heat rather than insulating it. Image, Chelsea Turner/MIT

Plastics are excellent insulators, meaning they can efficiently trap heat — a quality that can be an advantage in something like a coffee cup sleeve. But this insulating property is less desirable in products such as plastic casings for laptops and mobile phones, which can overheat, in part because the coverings trap the heat that the devices produce.

Now a team of engineers at MIT has developed a polymer thermal conductor — a plastic material that, however counterintuitively, works as a heat conductor, dissipating heat rather than insulating it. The new polymers, which are lightweight and flexible, can conduct 10 times as much heat as most commercially used polymers.

“Traditional polymers are both electrically and thermally insulating. The discovery and development of electrically conductive polymers has led to novel electronic applications such as flexible displays and wearable biosensors,” says Yanfei Xu, a postdoc in MIT’s Department of Mechanical Engineering. “Our polymer can thermally conduct and remove heat much more efficiently. We believe polymers could be made into next-generation heat conductors for advanced thermal management applications, such as a self-cooling alternative to existing electronics casings.”

Xu and a team of postdocs, graduate students, and faculty, have published their results March 30, 2018, in Science Advances. The team includes Xiaoxue Wang, who contributed equally to the research with Xu, along with Jiawei Zhou, Bai Song, Elizabeth Lee, and Samuel Huberman; Zhang Jiang, physicist at Argonne National Laboratory; Karen Gleason, associate provost of MIT and the Alexander I. Michael Kasser Professor of Chemical Engineering; and Gang Chen, head of MIT’s Department of Mechanical Engineering and the Carl Richard Soderberg Professor of Power Engineering.

Stretching spaghetti

If you were to zoom in on the microstructure of an average polymer, it wouldn’t be difficult to see why the material traps heat so easily. At the microscopic level, polymers are made from long chains of monomers, or molecular units, linked end to end. These chains are often tangled in a spaghetti-like ball. Heat carriers have a hard time moving through this disorderly mess and tend to get trapped within the polymeric snarls and knots.

And yet, researchers have attempted to turn these natural thermal insulators into conductors. For electronics, polymers would offer a unique combination of properties, as they are lightweight, flexible, and chemically inert. Polymers are also electrically insulating, meaning they do not conduct electricity, and can therefore be used to prevent devices such as laptops and mobile phones from short-circuiting in their users’ hands.

Several groups have engineered polymer conductors in recent years, including Chen’s group, which in 2010 invented a method to create “ultradrawn nanofibers” from a standard sample of polyethylene. The technique stretched the messy, disordered polymers into ultrathin, ordered chains — much like untangling a string of holiday lights. Chen found that the resulting chains enabled heat to skip easily along and through the material, and that the polymer conducted 300 times as much heat compared with ordinary plastics.

But the insulator-turned-conductor could only dissipate heat in one direction, along the length of each polymer chain. Heat couldn’t travel between polymer chains, due to weak Van der Waals forces — a phenomenon that essentially attracts two or more molecules close to each other. Xu wondered whether a polymer material could be made to scatter heat away, in all directions.

Xu conceived of the current study as an attempt to engineer polymers with high thermal conductivity, by simultaneously engineering intramolecular and intermolecular forces — a method that she hoped would enable efficient heat transport along and between polymer chains.

The team ultimately produced a heat-conducting polymer known as polythiophene, a type of conjugated polymer that is commonly used in many electronic devices.

Hints of heat in all directions

Xu, Chen, and members of Chen’s lab teamed up with Gleason and her lab members to develop a new way to engineer a polymer conductor using oxidative chemical vapor deposition (oCVD), whereby two vapors are directed into a chamber and onto a substrate, where they interact and form a film. “Our reaction was able to create rigid chains of polymers, rather than the twisted, spaghetti-like strands in normal polymers.” Xu says.

In this case, Wang flowed the oxidant into a chamber, along with a vapor of monomers — individual molecular units that, when oxidized, form into the chains known as polymers.

“We grew the polymers on silicon/glass substrates, onto which the oxidant and monomers are adsorbed and reacted, leveraging the unique self-templated growth mechanism of CVD technology," Wang says.

Wang produced relatively large-scale samples, each measuring 2 square centimeters — about the size of a thumbprint.

“Because this sample is used so ubiquitously, as in solar cells, organic field-effect transistors, and organic light-emitting diodes, if this material can be made to be thermally conductive, it can dissipate heat in all organic electronics,” Xu says.

The team measured each sample’s thermal conductivity using time-domain thermal reflectance — a technique in which they shoot a laser onto the material to heat up its surface and then monitor the drop in its surface temperature by measuring the material’s reflectance as the heat spreads into the material.

“The temporal profile of the decay of surface temperature is related to the speed of heat spreading, from which we were able to compute the thermal conductivity,” Zhou says.

On average, the polymer samples were able to conduct heat at about 2 watts per meter per kelvin — about 10 times faster than what conventional polymers can achieve. At Argonne National Laboratory, Jiang and Xu found that polymer samples appeared nearly isotropic, or uniform. This suggests that the material’s properties, such as its thermal conductivity, should also be nearly uniform. Following this reasoning, the team predicted that the material should conduct heat equally well in all directions, increasing its heat-dissipating potential.

Going forward, the team will continue exploring the fundamental physics behind polymer conductivity, as well as ways to enable the material to be used in electronics and other products, such as casings for batteries, and films for printed circuit boards.

“We can directly and conformally coat this material onto silicon wafers and different electronic devices” Xu says. “If we can understand how thermal transport [works] in these disordered structures, maybe we can also push for higher thermal conductivity. Then we can help to resolve this widespread overheating problem, and provide better thermal management.”

This research was supported, in part, by the U.S. Department of Energy — Basic Energy Sciences and the MIT Deshpande Center.

– Jennifer Chu | MIT News Office 
March 30, 2018

Tuesday, 27 March 2018 15:53

Featured video: Magical Bob

A fascination with magic leads Institute Professor Robert Langer to solve world problems using the marvels of chemical engineering.

A fascination with magic leads Institute Professor Robert Langer to solve world problems using the marvels of chemical engineering. Video. Lillie Paquette, School of Engineering

As a child, Institute Professor Robert S. Langer was captivated by the “magic” of the chemical reactions in a toy chemistry set. Decades later, he continues to be enchanted by the potential of chemical engineering. He is the most cited engineer in the world, and shows no signs of slowing down, despite four decades of ground-breaking work in drug delivery and polymer research.

Langer explains, “For me, magic has been discovering and inventing things. Discovering substances that can stop blood vessels from growing in the body, which can ultimately lead to treatments for cancer and blindness.”

The Langer Lab has had close to 1,000 students and postdocs go through its doors. Hundreds are now professors around the world. Many have started companies.

“I’m very proud of all of them,” says Langer. “I hope that I help them a little bit. That’s what we try to do.”back to newsletter

– MIT News Office
March 27, 2018

Cutting kirigami-style slits in stretchy films could make for bandages, heat pads, and wearable electronics that adhere to flexible surfaces.
MIT Kirigami Film Web
Ruike Zhao, a postdoc in MIT’s Department of Mechanical Engineering, says kirigami-patterned adhesives may enable a whole swath of products, from everyday medical bandages to wearable and soft electronics. Image courtesy of researchers.

Scraped up knees and elbows are tricky places to securely apply a bandage. More often than not, the adhesive will peel away from the skin with just a few bends of the affected joint.

Now MIT engineers have come up with a stickier solution, in the form of a thin, lightweight, rubber-like film. The adhesive film can stick to highly deformable regions of the body, such as the knee and elbow, and maintain its hold even after 100 bending cycles. The key to the film’s clinginess is a pattern of slits that the researchers have cut into the film, similar to the cuts made in a paper-folding art form known as kirigami.

The researchers attached the “kirigami film” to a volunteer’s knee and found that each time she bent her knee, the film’s slits opened at the center, in the region of the knee with the most pronounced bending, while the slits at the edges remained closed, allowing the film to remain bonded to the skin. The kirigami cuts give the film not only stretch, but also better grip: The cuts that open release tension that would otherwise cause the entire film to peel away from the skin.

To demonstrate potential applications, the group fabricated a kirigami-patterned adhesive bandage, as well as a heat pad consisting of a kirigami film threaded with heating wires. With the application of a 3-volt power supply, the pad maintains a steady temperature of 100 degrees Fahrenheit. The group has also engineered a wearable electronic film outfitted with light-emitting diodes. All three films can function and stick to the skin, even after 100 knee bends.

Ruike Zhao, a postdoc in MIT’s Department of Mechanical Engineering, says kirigami-patterned adhesives may enable a whole swath of products, from everyday medical bandages to wearable and soft electronics.

“Currently in the soft electronics field, people mostly attach devices to regions with small deformations, but not in areas with large deformations such as joint regions, because they would detach,” Ruike says. “I think kirigami film is one solution to this problem commonly found in adhesives and soft electronics.”

Ruike is the lead author of a paper published online this month in the journal Soft Matter. Her co-authors are graduate students Shaoting Lin and Hyunwoo Yuk, along with Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering.

 


Small, “kirigami” slits in polymer film enable the material to stick to the skin, even after 100 knee bends, compared to the same film without slits, which debonds after just one bending cycle.

Adhesion from an art form

In August 2016, Ruike and her colleagues were approached by representatives from a medical supply company in China, who asked the group to develop an improved version of a popular pain-relieving bandage that the company currently manufactures.

“Adhesives like these bandages are very commonly used in our daily life, but when you try to attach them to places that encounter large, inhomogenous bending motion, like elbows and knees, they usually detach,” Ruike says. “It’s a huge problem for the company, which they asked us to solve.”

The team considered kirigami as a potential solution. Originally an Asian folk art, kirigami is the practice of cutting intricate patterns into paper and folding this paper, much like origami, to create beautiful, elaborate three-dimensional structures. More recently, some scientists have been exploring kirigami as a way to develop new, functional materials.

“In most cases, people make cuts in a structure to make it stretchable,” Ruike says. “But we are the first group to find, with a systematic mechanism study, that a kirigami design can improve a material’s adhesion.”

The researchers fabricated thin kirigami films by pouring a liquid elastomer, or rubber solution, into 3-D-printed molds. Each mold was printed with rows of offset grooves of various spacings, which the researchers then filled with the rubber solution. Once cured and lifted out of the molds, the thin elastomer layers were studded with rows of offset slits. The researchers say the film can be made from a wide range of materials, from soft polymers to hard metal sheets.

Ruike applied a thin­­­ adhesive coating, similar to what is applied to bandages, to each film before attaching it to a volunteer’s knee. She took note of each film’s ability to stick to the knee after repeated bending, compared with an elastomer film that had no kirigami patterns. After just one cycle, the plain, continuous film quickly detached, whereas the kirigami film maintained its hold, even after 100 knee bends.

A balance in design

To find out why kirigami cuts enhance a material’s adhesive properties, the researchers first bonded a kirigami film to a polymer surface, then subjected the material to stretch tests. They measured the amount of stretch a kirigami film can undergo before peeling away from the polymer surface — a measurement they used to calculate the material’s critical “energy-release rate,” a quantity to evaluate detaching.

They found that this energy-release rate varied throughout a single film: When they pulled the film from either end like an accordion, the slits toward the middle exhibited a higher energy-release rate and were first to peel open under less stretch. In contrast, the slits at either end of the film continued to stick to the underlying surface and remained closed.

The researchers stretched kirigami films and measured their “energy release rate,” or the critical amount of stretch a film can handle before peeling away from its surface.

Through these experiments, Ruike identified three main parameters that give kirigami films their adhesive properties: shear-lag, in which shear deformation of film can reduce the strain on other parts of the film; partial debonding, in which the film segments around an open slit maintain a partial bond to the underlying surface; and inhomogenous deformation, in which a film can maintain its overall adhesion, even as parts of its underlying surface may bend and stretch more than others.

Depending on the application, Ruike says researchers can use the team’s findings as a design blueprint to identify the best pattern of cuts and the optimal balance of the three parameters, for a given application.

“These three parameters will help guide the design of soft, advanced materials,” Ruike says. “You can always design other patterns, just like folk art. There are so many solutions that we can think of. Just follow the mechanical guidance for an optimized design, and you can achieve a lot of things.”

Ruike and her colleagues have filed a patent on their technique and are continuing to collaborate with the medical supply company, which is currently making plans to manufacture medicine patches made from kirigami films.
“They make this pain-relieving pad that’s pretty popular in China — even my parents use it,” Ruike says. “So it’s super exciting.”

The team is now branching out to explore other materials on which to pattern kirigami cuts.
“The current films are purely elastomers,” Ruike says. “We want to change the film material to gels, which can directly diffuse medicine into the skin. That’s our next step.”

This research was supported, in part, by the National Science Foundation and the Tibet Cheezheng Tibetan Medicine Co. Ltd.

– Jennifer Chu | MIT News Office back to newsletter
March 27, 2018

Design principles could point to better electrolytes for next-generation lithium batteries.
MIT Lithium Electrolytes 01 PRESS Web
Diagram illustrates the crystal lattice of a proposed battery electrolyte material called Li3PO4. The researchers found that measuring how vibrations of sound move through the lattice could reveal how well ions – electrically charged atoms or molecules – could travel through the solid material, and therefore how they would work in a real battery. In this diagram, the oxygen atoms are shown in red, the purple pyramid-like shapes are phosphate (PO4) molecules. The orange and green spheres are ions of lithium. Image: Sokseiha Muy

 A new approach to analyzing and designing new ion conductors — a key component of rechargeable batteries — could accelerate the development of high-energy lithium batteries, and possibly other energy storage and delivery devices such as fuel cells, researchers say.

The new approach relies on understanding the way vibrations move through the crystal lattice of lithium ion conductors and correlating that with the way they inhibit ion migration. This provides a way to discover new materials with enhanced ion mobility, allowing rapid charging and discharging. At the same time, the method can be used to reduce the material’s reactivity with the battery’s electrodes, which can shorten its useful life. These two characteristics — better ion mobility and low reactivity — have tended to be mutually exclusive.

The new concept was developed by a team led by W.M. Keck Professor of Energy Yang Shao-Horn, graduate student Sokseiha Muy, recent graduate John Bachman PhD ’17, and Research Scientist Livia Giordano, along with nine others at MIT, Oak Ridge National Laboratory, and institutions in Tokyo and Munich. Their findings were reported in the journal Energy and Environmental Science.

The new design principle has been about five years in the making, Shao-Horn says. The initial thinking started with the approach she and her group have used to understand and control catalysts for water splitting, and applying it to ion conduction — the process that lies at the heart of not only rechargeable batteries, but also other key technologies such as fuel cells and desalination systems. While electrons, with their negative charge, flow from one pole of the battery to the other (thus providing power for devices), positive ions flow the other way, through an electrolyte, or ion conductor, sandwiched between those poles, to complete the flow.

Typically, that electrolyte is a liquid. A lithium salt dissolved in an organic liquid is a common electrolyte in today’s lithium-ion batteries. But that substance is flammable and has sometimes caused these batteries to catch fire. The search has been on for a solid material to replace it, which would eliminate that issue.

A variety of promising solid ion conductors exist, but none is stable when in contact with both the positive and negative electrodes in lithium-ion batteries, Shao-Horn says. Therefore, seeking new solid ion conductors that have both high ion conductivity and stability is critical. But sorting through the many different structural families and compositions to find the most promising ones is a classic needle in a haystack problem. That’s where the new design principle comes in.

The idea is to find materials that have ion conductivity comparable to that of liquids, but with the long-term stability of solids. The team asked, “What is the fundamental principle? What are the design principles on a general structural level that govern the desired properties?” Shao-Horn says. A combination of theoretical analysis and experimental measurements has now yielded some answers, the researchers say.

“We realized that there are a lot of materials that could be discovered, but no understanding or common principle that allows us to rationalize the discovery process,” says Muy, the paper’s lead author. “We came up with an idea that could encapsulate our understanding and predict which materials would be among the best.”

MIT Lithium Electrolytes A1 PRESS Web
Diagram illustrates the crystal lattice of a proposed battery electrolyte material called Li3PO4. The researchers found that measuring how vibrations of sound move through the lattice could reveal how well ions – electrically charged atoms or molecules – could travel through the solid material, and therefore how they would work in a real battery. In this diagram, the purple pyramid-like shapes are phosphate (PO4) molecules. The orange and green spheres are ions of lithium.

The key was to look at the lattice properties of these solid materials’ crystalline structures. This governs how vibrations such as waves of heat and sound, known as phonons, pass through materials. This new way of looking at the structures turned out to allow accurate predictions of the materials’ actual properties. “Once you know [the vibrational frequency of a given material], you can use it to predict new chemistry or to explain experimental results,” Shao-Horn says.

The researchers observed a good correlation between the lattice properties determined using the model and the lithium ion conductor material’s conductivity. “We did some experiments to support this idea experimentally” and found the results matched well, she says.

They found, in particular, that the vibrational frequency of lithium itself can be fine-tuned by tweaking its lattice structure, using chemical substitution or dopants to subtly change the structural arrangement of atoms.
The new concept can now provide a powerful tool for developing new, better-performing materials that could lead to dramatic improvements in the amount of power that could be stored in a battery of a given size or weight, as well as improved safety, the researchers say. Already, they used the method to find some promising candidates. And the techniques could also be adapted to analyze materials for other electrochemical processes such as solid-oxide fuel cells, membrane based desalination systems, or oxygen-generating reactions.

The team included Hao-Hsun Chang at MIT; Douglas Abernathy, Dipanshu Bansal, and Olivier Delaire at Oak Ridge; Santoshi Hori and Ryoji Kanno at Tokyo Institute of Technology; and Filippo Maglia, Saskia Lupart, and Peter Lamp at Research Battery Technology at BMW Group in Munich. The work was supported by BMW, the National Science Foundation, and the U.S. Department of Energy.

back to newsletter– David L. Chandler | MIT News Office
March 25, 2018

Monday, 26 March 2018 13:42

2018 Summer Scholars selected

MIT Materials Research Laboratory announces 12 recipients of Research Experience for Undergraduates (REU) internships.
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Twelve recipients of Research Experience for Undergraduates (REU) internships will select their own projects from MIT faculty presentations given during the first few days of the Summer Scholars program. Image, Denis Paiste, MRL.

The MIT Materials Research Laboratory [MRL] has selected 12 top-ranking undergraduates to conduct graduate-level research on the MIT campus in Cambridge, Mass., from June 17 to August 11, 2018.

Interns will select their own projects from MIT faculty presentations given during the first few days of the program. Last year’s group, for example, conducted supervised research on projects in materials science, photonics, energy, and biomedical fields.

This year’s Summer Scholars and their major fields of study are:

- Danielle Beatty, University of Utah, Materials Science and Engineering

- Alvin Chang, Oregon State University, Chemical Engineering, Biological Engineering, with minor in Entrepreneurship

- Simon Egner, University of Illinois at Urbana-Champaign, Materials Science and Engineering

- Elizabeth Hallett, University of Arkansas-Fayetteville, Chemical Engineering

- Julianna LaLane, University of Puerto Rico at Mayaguez, Mechanical Engineering

- Michael Molinski, University of Rhode Island, Chemical Engineering

- Abigail Nason, University of Florida, Materials Science and Engineering,

- Fernando Nieves Munoz, University of Puerto Rico, Mayaguez, Mechanical Engineering

- Sarai Patterson, University of Utah, Materials Science and Engineering

- Sabrina Shen, Johns Hopkins University, Materials Science and Engineering

- Ryan Tollefsen, Oregon State University, Physics

- Ekaterina Tsotsos, Brown University, Materials Engineering

Summer Scholars serve as interns through the MIT MRL and are supported in part by the National Science Foundation’s Research Experience for Undergraduates (REU) program, which is administered by the MIT Materials Research Science and Engineering Center, and the AIM Photonics Academy.

The program, started in 1983, has brought hundreds of the best science and engineering undergraduates in the country to MIT for graduate-level materials research.

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MIT graduate engineering, business, science programs ranked highly by U.S. News and World Report for 2019.
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MIT’s graduate program in engineering has again earned a No. 1 spot in U.S. News and World Report’s annual rankings, a place it has held since 1990, when the magazine first ranked such programs. Pictured is MIT Lobby 7. Photo by Jake Belcher

MIT’s graduate program in engineering has again earned a No. 1 spot in U.S. News and World Report’s annual rankings, a place it has held since 1990, when the magazine first ranked such programs.

The MIT Sloan School of Management also placed highly, occupying the No. 5 spot for the best graduate business program.

This year, U.S. News also ranked the nation’s top PhD programs in the sciences, which it last evaluated in 2014. The magazine awarded No. 1 spots to MIT programs in biology (tied with Stanford University and the University of California at Berkeley), computer science (tied with Carnegie Mellon University, Stanford, and Berkeley), and physics (tied with Stanford). No. 2 spots went to MIT programs in chemistry (tied with Harvard University, Stanford, and Berkeley), earth sciences (tied with Stanford and Berkeley); and mathematics (tied with Harvard, Stanford, and Berkeley).

Among individual engineering disciplines, MIT placed first in six areas: aerospace/aeronautical/astronautical engineering (tied with Caltech), chemical engineering, computer engineering, electrical/electronic/communications engineering (tied with Stanford and Berkeley), materials engineering, and mechanical engineering. It placed second in nuclear engineering.

In the rankings of individual MBA specialties, MIT placed first in information systems and production/operations. It placed second in supply chain/logistics and third in entrepreneurship.

U.S. News does not issue annual rankings for all doctoral programs but revisits many every few years. This year, MIT ranked in the top five for 24 of the 37 science disciplines evaluated.

The magazine bases its rankings of graduate schools of engineering and business on two types of data: reputational surveys of deans and other academic officials, and statistical indicators that measure the quality of a school’s faculty, research, and students. The magazine’s less-frequent rankings of programs in the sciences, social sciences, and humanities are based solely on reputational surveys.

back to newsletterMIT News Office
March 20, 2018

MIT professor devises new ways to generate useful chemicals and fuels from renewable resources.
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Newly tenured MIT Department of Chemical Engineering faculty member Yuriy Roman says, "The most rewarding aspect of my profession is to work with these extremely talented and bright students. Image, M. Scott Brauer.

A couple of years into graduate school, Yuriy Roman had what he calls a “tipping point” in his career. He realized that all of the classes he had taken were leading him toward a deep understanding of the concepts he needed to design his own solutions to chemical problems.

“All the classes I had taken suddenly came together, and that’s when I started understanding why I needed to know something about thermodynamics, kinetics, and transport. All of these concepts that I had seen as more theoretical things in my classes, I could now see being applied together to solve a problem. That really was what changed everything for me,” he says.

As a newly tenured faculty member in MIT’s Department of Chemical Engineering, Roman now tries to guide his students toward their own tipping points.
“It’s amazing to see it happen with my students,” says Roman, noting that working with students is one of his favorite things about being an MIT professor. His students also make major contributions to his lab’s mission: coming up with new catalysts to produce fuels, plastics, and other useful substances in a more efficient, sustainable manner.

“To me, the most rewarding aspect of my profession is to work with these extremely talented and bright students,” Roman says. “They really are great at coming up with outside-of-the-box concepts, and I love that. I think MIT’s biggest asset is precisely that, the students. To me it’s a pleasure to work with them and learn from them as well, and hopefully have the opportunity to teach them some of the things that I know.”

Chemical synthesis

Roman, who grew up in Mexico City, loved chemistry from a young age. “I just liked to play with things like soap and bleach, which maybe wasn’t the safest thing,” he recalls. Another favorite activity was juicing cabbages to produce a pH indicator. (Red cabbage contains a chemical called anthocyanin that changes color when exposed to acidic or basic environments.)

Roman’s mother was originally from Belarus, and with his multicultural background he developed a strong interest in learning about other cultures and visiting other countries. He won a full scholarship to Monterrey Institute of Technology and Higher Education, in Mexico, for high school and college, but during his first year of college, he became interested in going abroad to finish his degree.

A friend who was then an undergraduate at MIT encouraged Roman to apply to schools in the United States, and he ended up transferring to the University of Pennsylvania.

“My parents were very surprised. In Mexico, it is common to live with your parents long after finishing college. The concept of leaving for college is almost nonexistent,” Roman says.

Roman decided to study chemical engineering, allowing him to combine his love for chemical reactions and his desire to follow in the footsteps of a brother who was an engineer. After graduating, he planned to look for a job in the chemical industry, but his then-girlfriend, now his wife, was planning to begin medical school. She suggested that he go to graduate school with her, so they both ended up attending the University of Wisconsin at Madison.

There, Roman studied with James Dumesic, a chemistry professor who works on biofuels. For his PhD thesis, Roman devised a process to generate a chemical called hydroxymethylfurfural (HMF) from sugars derived from biomass. HMF is a “platform chemical” that can be converted into many different end products, including fuels.

After finishing graduate school, Roman thought he would go to work for a chemical company, but at Dumesic’s suggestion he decided to go into academia instead.
“When I started interviewing at different universities, I realized that as a professor, you can have a lot of freedom to explore ideas and tackle problems long-term, and you can still have a lot of contact with industry,” he says. “You have more control over your time and where you spend it, in terms of investing effort toward basic science.”

Out of graduate school, he got a job offer at MIT but first spent two years doing a postdoc at Caltech, while his wife did her residency at the University of California at Los Angeles. Working with Mark Davis, a professor of chemical engineering, Roman began studying materials called zeolites, which have pores the same size as many common molecules. Confining molecules in these pores allows for certain chemical reactions to occur much faster than they otherwise would, Roman says.

Davis also instilled in Roman the importance of designing his own catalysts rather than relying on those developed by others, which allows for more control over chemical reactions and the resulting materials. While many research groups focus either on designing catalysts or on using existing catalysts to come up with novel ways to synthesize materials, Roman believes it is critical to work on both. 

“When you are in control of synthesizing your own catalysts, you can do much more systematic studies. You have the ability to manipulate things at will,” he says. “It’s working at this juncture of synthesis and catalysis that is the key to discovering new chemistry.”

Green chemistry

After arriving at MIT in 2010, Roman launched his lab with a focus on designing catalysts that can generate new and interesting materials. One key area of research is the conversion of biomass components, such as lignin, into fuels and chemicals. One of the biggest challenges in this type of synthesis is to selectively remove oxygen atoms from these molecules, which usually have many more oxygen atoms than fuels do.

During a brainstorming session, Roman and his students came up with the idea of using a metal oxide catalyst in which some oxygen atoms were removed from the surface, creating small pockets known as “vacancies.” Oxygenated molecules can be precisely anchored in those vacancies, allowing their carbon-oxygen bonds to be easily broken so the oxygen can be replaced with hydrogen.

In another project, Roman’s lab developed a more sustainable alternative to catalysts made from precious metals such as platinum and palladium. These metals are used in many renewable-energy technologies, including fuel cells and lithium-air batteries, but they are among the Earth’s scarcest metals.

“If we were to go from our current fleet of vehicles with internal combustion engines to a fuel cell fleet, there’s not enough platinum in the world to sustain that amount,” Roman says. “You need to use Earth-abundant materials because there simply aren’t enough of these other precious materials to do it.”

In 2014, Roman and his students showed that they could create powerful catalysts from compounds called metal carbides, made from plentiful metals such as tungsten, coated with just a thin layer of a rare metal such as platinum.

Developing and promoting this kind of sustainable technology is one of Roman’s biggest research priorities.

“It’s a tremendous battle because the energy sector is just so large. The scale is so big and the infrastructure that’s already in place for petroleum-based fuel is so extensive. But it’s important for us to develop technologies for renewable resources and really curb our emissions of greenhouse gases,” he says. “Big, hard problems. That’s what we’re going after.”

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Anne Trafton | MIT News Office
March 22, 2018

With an atomic structure resembling a Japanese basketweaving pattern, “kagome metal” exhibits exotic, quantum behavior.

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An illustration depicting a kagome metal — an electrically conducting crystal, made from layers of iron and tin atoms, with each atomic layer arranged in the repeating pattern of a kagome lattice. Images by Felice Frankel; Illustration overlays by Chelsea Turner

A motif of Japanese basketweaving known as the kagome pattern has preoccupied physicists for decades. Kagome baskets are typically made from strips of bamboo woven into a highly symmetrical pattern of interlaced, corner-sharing triangles.

If a metal or other conductive material could be made to resemble such a kagome pattern at the atomic scale, with individual atoms arranged in similar triangular patterns, it should in theory exhibit exotic electronic properties.

In a paper published March 19, 2018, in Nature, physicists from MIT, Harvard University, and Lawrence Berkeley National Laboratory report that they have for the first time produced a kagome metal — an electrically conducting crystal, made from layers of iron and tin atoms, with each atomic layer arranged in the repeating pattern of a kagome lattice.

When they flowed a current across the kagome layers within the crystal, the researchers observed that the triangular arrangement of atoms induced strange, quantum-like behaviors in the passing current. Instead of flowing straight through the lattice, electrons instead veered, or bent back within the lattice.

This behavior is a three-dimensional cousin of the so-called Quantum Hall effect, in which electrons flowing through a two-dimensional material will exhibit a “chiral, topological state,” in which they bend into tight, circular paths and flow along edges without losing energy.

“By constructing the kagome network of iron, which is inherently magnetic, this exotic behavior persists to room temperature and higher,” says Joseph Checkelsky, assistant professor of physics at MIT. “The charges in the crystal feel not only the magnetic fields from these atoms, but also a purely quantum-mechanical magnetic force from the lattice. This could lead to perfect conduction, akin to superconductivity, in future generations of materials.”

To explore these findings, the team measured the energy spectrum within the crystal, using a modern version of an effect first discovered by Heinrich Hertz and explained by Einstein, known as the photoelectric effect.

“Fundamentally, the electrons are first ejected from the material’s surface and are then detected as a function of takeoff angle and kinetic energy,” says Riccardo Comin, an assistant professor of physics at MIT. “The resulting images are a very direct snapshot of the electronic levels occupied by electrons, and in this case they revealed the creation of nearly massless ‘Dirac’ particles, an electrically charged version of photons, the quanta of light.”

The spectra revealed that electrons flow through the crystal in a way that suggests the originally massless electrons gained a relativistic mass, similar to particles known as massive Dirac fermions. Theoretically, this is explained by the presence of the lattice’s constituent iron and tin atoms. The former are magnetic and give rise to a “handedness,” or chirality. The latter possess a heavier nuclear charge, producing a large local electric field. As an external current flows by, it senses the tin’s field not as an electric field but as a magnetic one, and bends away.

The research team was led by Checkelsky and Comin, as well as graduate students Linda Ye and Min Gu Kang in collaboration with Liang Fu, the Biedenharn Associate Professor of Physics, and postdoc Junwei Liu. The team also includes Christina Wicker ’17, research scientist Takehito Suzuki of MIT, Felix von Cube and David Bell of Harvard, and Chris Jozwiak, Aaron Bostwick, and Eli Rotenberg of Lawrence Berkeley National Laboratory.

“No alchemy required”

Physicists have theorized for decades that electronic materials could support exotic Quantum Hall behavior with their inherent magnetic character and lattice geometry. It wasn’t until several years ago that researchers made progress in realizing such materials.

“The community realized, why not make the system out of something magnetic, and then the system’s inherent magnetism could perhaps drive this behavior,” says Checkelsky, who at the time was working as a researcher at the University of Tokyo.

This eliminated the need for laboratory produced fields, typically 1 million times as strong as the Earth’s magnetic field, needed to observe this behavior.

“Several research groups were able to induce a Quantum Hall effect this way, but still at ultracold temperatures a few degrees above absolute zero — the result of shoehorning magnetism into a material where it did not naturally occur,” Checkelsky says.

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Assistant professor of physics at MIT Joe Checkelsky (left to right), graduate students Linda Ye and Min Gu Kang, and assistant professor of physics at MIT Riccardo Comin. Image, Takehito

At MIT, Checkelsky has instead looked for ways to drive this behavior with “instrinsic magnetism.” A key insight, motivated by the doctoral work of Evelyn Tang PhD ’15 and Professor Xiao-Gang Wen, was to seek this behavior in the kagome lattice. To do so, first author Ye ground together iron and tin, then heated the resulting powder in a furnace, producing crystals at about 750 degrees Celsius — the temperature at which iron and tin atoms prefer to arrange in a kagome-like pattern. She then submerged the crystals in an ice bath to enable the lattice patterns to remain stable at room temperature.

“The kagome pattern has big empty spaces that might be easy to weave by hand, but are often unstable in crystalline solids which prefer the best packing of atoms,” Ye says. “The trick here was to fill these voids with a second type of atom in a structure that was at least stable at high temperatures. Realizing these quantum materials doesn’t need alchemy, but instead materials science and patience.”

Bending and skipping toward zero-energy loss

Once the researchers grew several samples of crystals, each about a millimeter wide, they handed the samples off to collaborators at Harvard, who imaged the individual atomic layers within each crystal using transmission electron microscopy. The resulting images revealed that the arrangement of iron and tin atoms within each layer resembled the triangular patterns of the kagome lattice. Specifically, iron atoms were positioned at the corners of each triangle, while a single tin atom sat within the larger hexagonal space created between the interlacing triangles.

Ye then ran an electric current through the crystalline layers and monitored their flow via electrical voltages they produced. She found that the charges deflected in a manner that seemed two-dimensional, despite the three-dimensional nature of the crystals. The definitive proof came from the photoelectron experiments conducted by co-first author Kang who, in concert with the LBNL team, was able to show that the electronic spectra corresponded to effectively two-dimensional electrons.

“As we looked closely at the electronic bands, we noticed something unusual,” Kang adds. “The electrons in this magnetic material behaved as massive Dirac particles, something that had been predicted long ago but never been seen before in these systems.”

“The unique ability of this material to intertwine magnetism and topology suggests that they may well engender other emergent phenomena,” Comin says. “Our next goal is to detect and manipulate the edge states which are the very consequence of the topological nature of these newly discovered quantum electronic phases.”

Looking further, the team is now investigating ways to stabilize other more highly two-dimensional kagome lattice structures. Such materials, if they can be synthesized, could be used to explore not only devices with zero energy loss, such as dissipationless power lines, but also applications toward quantum computing.

“For new directions in quantum information science there is a growing interest in novel quantum circuits with pathways that are dissipationless and chiral,” Checkelsky says. “These kagome metals offer a new materials design pathway to realizing such new platforms for quantum circuitry.”

This research was supported in part by the Gordon and Betty Moore Foundation and the National Science Foundation.

– Jennifer Chu | MIT News Office
March 19, 2018

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