Scientists Demonstrate Pathway to Forerunner of Rugged Nanotubes That Could Lead to Widespread Industrial Fabrication

 

Scientists have identified a chemical pathway to an innovative insulating nanomaterial that could lead to large-scale industrial production for a variety of uses – including in spacesuits and military vehicles. The nanomaterial — thousands of times thinner than a human hair, stronger than steel, and noncombustible — could block radiation to astronauts and help shore up military vehicle armor, for example.

Collaborative researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have proposed a step-by-step chemical pathway to the precursors of this nanomaterial, known as boron nitride nanotubes (BNNT), which could lead to their large-scale production. 

“Pioneering work”

The breakthrough brings together plasma physics and quantum chemistry and is part of the expansion of research at PPPL. “This is pioneering work that takes the Laboratory in new directions,” said PPPL physicist Igor Kaganovich, principal investigator of the BNNT project and co-author of the paper that details the results in the journal Nanotechnology.

Collaborators identified the key chemical pathway steps as the formation of molecular nitrogen and small clusters of boron, which can chemically react together as the temperature created by a plasma jet cools, said lead author Yuri Barsukov of the Peter the Great St. Petersburg Polytechnic University. He developed the chemical reaction pathways by performing quantum chemistry simulations with the assistance of Omesh Dwivedi, a PPPL intern from Drexel University, and Sierra Jubin, a graduate student in the Princeton Program in Plasma Physics.

The interdisciplinary team included Alexander Khrabry, a former PPPL researcher now at Lawrence Livermore National Laboratory who developed a thermodynamic code used in this research, and PPPL physicist Stephane Ethier who helped the students compile the software and set up the simulations. 

The results solved the mystery of how molecular nitrogen, which has the second strongest chemical bond among diatomic, or double-atom molecules, can nonetheless break apart through reactions with boron to form various boron-nitride molecules, Kaganovich said. “We spent considerable amount of time thinking about how to get boron – nitride compounds from a mixture of boron and nitrogen,” he said. “What we found was that small clusters of boron, as opposed to much larger boron droplets, readily interact with nitrogen molecules. That’s why we needed a quantum chemist to go through the detailed quantum chemistry calculations with us.”

BNNTs have properties similar to carbon nanotubes, which are produced by the ton and found in everything from sporting goods and sportswear to dental implants and electrodes. But the greater difficulty of producing BNNTs has limited their applications and availability. 

Chemical pathway

Demonstration of a chemical pathway to the formation of BNNT precursors could facilitate BNNT production. The process of BNNT synthesis begins when scientists use a 10,000-degree plasma jet to turn boron and nitrogen gas into plasma consisting of free electrons and atomic nuclei, or ions, embedded in a background gas. This shows how the process unfolds:

− The jet evaporates the boron while the molecular nitrogen largely stays intact;
− The boron condenses into droplets as the plasma cools;
− The droplets form small clusters as the temperature falls to a few thousand degrees;
− The critical next step is the reaction of nitrogen with small clusters of boron molecules to form boron-nitrogen chains;
− The chains grow longer by colliding with one another and fold into precursors of boron nitride nanotubes.

“During the high-temperature synthesis the density of small boron clusters is low,” Barsukov said. “This is the main impediment to large-scale production.”

The findings have opened a new chapter in BNNT nanomaterial synthesis. “After two years of work we have found the pathway,” Kaganovich said. “As boron condenses it forms big clusters that nitrogen doesn’t react with. But the process starts with small clusters that nitrogen reacts with and there is still a percentage of small clusters as the droplets grow larger,” he said.

“The beauty of this work,” he added, “is that since we had experts in plasma and fluid mechanics and quantum chemistry we could go through all these processes together in an interdisciplinary group. Now we need to compare possible BNNT output from our model with experiments. That will be the next stage of modeling.”

Read the original article on Princeton Plasma Physics Lab.

Researchers prove titanate nanotubes composites enhance photocatalysis of hydrogen – Better?

The titanate nanotubes (TNTs) composites enhanced the photocatalytic selectivity for H₂ generation from formic acid better than Pt/TiO₂. In addition, intensified electronic interactions occur between the components of TNTs and the Pt atoms in terms of the strong metal-support interaction, consequently influencing the behavior of photocatalysts. Therefore, the photocatalyst formed by Pt and TNTs has higher photocatalytic performance than TiO₂ from a 20% v/v methanol solution under UV and visible light irradiation. Credit: World Scientific Publishing

In a paper published in NANO, researchers from National Taiwan University examined the photocatalytic performances of titanate nanotubes (TNTs) against commonly-used titanium dioxide (TiO₂) and discovered superior performance of TNTs.

In the study, TiO₂ was used as a reference support compared with TNTs synthesized by a facile method. The results showed that Platinum (Pt/)TNTs fabricated using the microwave heating process enhanced the hydrogen evolution from methanol to a greater extent than Pt/TiO₂. The high surface area of TNTs can improve adsorption of methanol on the active site and prevent the formation of agglomerated fine Pt particles.

Additionally, the high surface area led to an increased contact area between Pt and Ti atoms, which enhanced the strong metal-support interaction and increased H₂ production performance. This is due to the absorption spectra of TNTs shifting toward the visible light region to a greater extent after loading Pt, thereby improving the selectivity of formic acid decomposition to CO₂. Therefore, Pt/TNTs, which have considerably high photocatalytic efficiency, are viable in further applications as promising photocatalysts.

The titanate nanotubes (TNTs) composites enhanced the photocatalytic selectivity for H₂ generation from formic acid better than Pt/TiO₂. In addition, intensified electronic interactions occur between the components of TNTs and the Pt atoms in terms of the strong metal-support interaction, consequently influencing the behavior of photocatalysts. Therefore, the photocatalyst formed by Pt and TNTs has higher photocatalytic performance than TiO₂ from a 20% v/v methanol solution under UV and visible light irradiation.

TNTs offer higher active surface area than TiO₂ nanoparticles. The high surface area provides short diffusion paths for electrons and holes, prompting them to transfer to the surface and reducing the recombination of electrons and holes. Also, X-ray Photoelectron Spectroscopy (XPS) results of the paper showed negative shifts of the Pt binding energies and positive shifts of Ti binding energies due to the strong metal-support interaction between Pt and TNTs. Thus, the remarkably high photocatalytic efficiency of TNT composites facilitates their application as promising photocatalysts.

Besides, it is worth noting that one mole of HCOOH decomposes into one mole of CO₂ and one mole of H₂, or one mole of CO and one mole of H₂O. Thus, it is important to increase the selectivity of formic acid decomposition for CO₂ evolution. The results show bare TNTs and Pt/TNTs resulted in lower CO generation than bare TiO₂ and Pt/TiO₂. This result may be attributed to the inability of CO to diffuse into the pores of TNTs because of the diameter difference, because the kinetic diameter of CO (0.38 nm) is larger than that of CO₂ (0.33 nm).

Will the different structure of the photocatalyst promote the photocatalytic selectivity of formic acid to H₂? The researchers prove tubular TNTs composites enhanced the photocatalytic hydrogen generation better than TiO₂.

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Explore further

When the structure of tunneling nanotubes (TNTs) challenges the very concept of cell

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More information: Hsiu-Yu Chen et al, Microwave-Assisted Synthesis of Titanate Nanotubes Loaded with Platinum with Enhanced Selectivity for Photocatalytic H2 Evolution from Methanol, Nano (2020). DOI: 10.1142/S1793292020501295

Provided by World Scientific Publishing

MIT: Carbon nanotube transistors make the leap from lab to factory floor

The next major revolution in computer chip technology is now a step closer to reality. Researchers have shown that carbon nanotube transistors can be made rapidly in commercial facilities, with the same equipment used to manufacture traditional silicon-based transistors – the backbone of today’s computing industry. 

Carbon nanotube field-effect transistors (CNFETs) are more energy-efficient than silicon field-effect transistors and could be used to build a new generation of three-dimensional microprocessors. But until now, these devices have been mostly restricted to academic laboratories with only small numbers produced.

However, in a new study this month – published in the journal Nature Electronics – scientists have demonstrated how CNFETs can be fabricated in large quantities on 200-millimetre wafers: the industry standard for computer chip design. The CNFETs were created in a commercial silicon manufacturing facility and a semiconductor foundry in the United States.

Having analysed the deposition technique used to make the CNFETs, a team at the Massachusetts Institute of Technology (MIT) developed a way of speeding up the fabrication process by more than 1,100 times compared to previous methods, while also reducing the cost.

Their technique deposited the carbon nanotubes edge to edge on wafers, with CFNET arrays of 14,400 by 14,400 distributed across multiple wafers.

Max Shulaker, an MIT assistant professor of electrical engineering and computer science, who has been designing CNFETs since his PhD days, says the new study represents “a giant step forward, to make that leap into production-level facilities.”

Bridging the gap between lab and industry is something that researchers “don’t often get a chance to do,” he added. “But it’s an important litmus test for emerging technologies.”

 

 

For decades, improvements in silicon-based transistor manufacturing have brought down prices and increased energy efficiency in computing. Concerns are mounting that this trend may be nearing its end, however, as increasing numbers of transistors packed into integrated circuits do not appear to be increasing energy efficiency at historic rates. CNFETs are an attractive alternative technology because they are “around an order of magnitude more energy efficient” than silicon-based transistors, says Shulaker.

While silicon-based transistors are typically made at temperatures of 450 to 500 degrees Celsius, CNFETs can be manufactured at near-room temperatures.

“This means that you can actually build layers of circuits right on top of previously fabricated layers of circuits, to create a 3D chip,” Shulaker explains. “You can’t do this with silicon-based technology, because it would melt the layers underneath.” 

A 3D computer chip, which might combine logic and memory functions, is projected to “beat the performance of a state-of-the-art 2D chip made from silicon by orders of magnitude,” he says.

One of the most effective ways to build CFNETs in the lab is a method for depositing nanotubes called incubation – illustrated below – where a wafer is submerged in a bath of nanotubes until the nanotubes stick to the wafer’s surface.

The performance of the CNFET depends in large part on the deposition process, explains co-author Mindy Bishop, a PhD student in the Harvard-MIT Health Sciences and Technology program. This affects both the number of carbon nanotubes on the surface of the wafer and their orientation. They are “either stuck onto the wafer in random orientations like cooked spaghetti, or all aligned in the same direction like uncooked spaghetti still in the package.”

Aligning the nanotubes perfectly in a CNFET leads to ideal performance, but alignment is difficult to obtain, says Bishop: “It’s really hard to lay down billions of tiny 1-nanometre diameter nanotubes in a perfect orientation across a large 200-millimetre wafer. To put these length scales into context, it’s like trying to cover the entire state of New Hampshire in perfectly oriented, dry spaghetti.” 

While the incubation method employed by the MIT team is unable to perfectly align every nanotube (perhaps a breakthrough in future years may achieve this?), their experiments showed that it delivers sufficiently high performance for a CNFET to outperform a traditional silicon-based transistor. 

Furthermore, careful observations revealed how to alter the process to make it more viable for large-scale commercial production. For instance, Bishop’s team found that “dry cycling”, a method of intermittently drying out the submerged wafer, could drastically reduce the incubation time – from 48 hours to 150 seconds. Another new method called artificial concentration through evaporation (ACE) deposited small amounts of nanotube solution on a wafer, instead of submerging the wafer in a tank. The slow evaporation of the solution increased the overall density of nanotubes on the wafer. 

The researchers worked with Analog Devices, a commercial silicon manufacturing facility, and SkyWater Technology, a semiconductor foundry, to fabricate CNFETs using the improved methods. They were able to use the same equipment that the two facilities use to make silicon-based wafers, while also ensuring that the nanotube solutions met strict chemical and contaminant requirements of the facilities. 

The next steps, already underway, will be to build different types of integrated circuits out of CNFETs in an industrial setting and explore some of the new functions that a 3D chip could offer, adds Shulaker. 

“The next goal is for this to transition from being academically interesting to something that will be used by folks, and I think this is a very important step in this direction,” he concludes.

MIT – A new approach to making airplane parts, minus the massive infrastructure

Carbon nanotube film produces aerospace-grade composites with no need for huge ovens or autoclaves.

A modern airplane’s fuselage is made from multiple sheets of different composite materials, like so many layers in a phyllo-dough pastry. Once these layers are stacked and molded into the shape of a fuselage, the structures are wheeled into warehouse-sized ovens and autoclaves, where the layers fuse together to form a resilient, aerodynamic shell.

Now MIT engineers have developed a method to produce aerospace-grade composites without the enormous ovens and pressure vessels. The technique may help to speed up the manufacturing of airplanes and other large, high-performance composite structures, such as blades for wind turbines.

The researchers detail their new method in a paper published today in the journal Advanced Materials Interfaces.

“If you’re making a primary structure like a fuselage or wing, you need to build a pressure vessel, or autoclave, the size of a two- or three-story building, which itself requires time and money to pressurize,” says Brian Wardle, professor of aeronautics and astronautics at MIT. “These things are massive pieces of infrastructure. Now we can make primary structure materials without autoclave pressure, so we can get rid of all that infrastructure.”

Wardle’s co-authors on the paper are lead author and MIT postdoc Jeonyoon Lee, and Seth Kessler of Metis Design Corporation, an aerospace structural health monitoring company based in Boston.

Out of the oven, into a blanket

In 2015, Lee led the team, along with another member of Wardle’s lab, in creating a method to make aerospace-grade composites without requiring an oven to fuse the materials together. Instead of placing layers of material inside an oven to cure, the researchers essentially wrapped them in an ultrathin film of carbon nanotubes (CNTs). When they applied an electric current to the film, the CNTs, like a nanoscale electric blanket, quickly generated heat, causing the materials within to cure and fuse together.

With this out-of-oven, or OoO, technique, the team was able to produce composites as strong as the materials made in conventional airplane manufacturing ovens, using only 1 percent of the energy.

The researchers next looked for ways to make high-performance composites without the use of large, high-pressure autoclaves — building-sized vessels that generate high enough pressures to press materials together, squeezing out any voids, or air pockets, at their interface.

“There’s microscopic surface roughness on each ply of a material, and when you put two plys together, air gets trapped between the rough areas, which is the primary source of voids and weakness in a composite,” Wardle says. “An autoclave can push those voids to the edges and get rid of them.”

Researchers including Wardle’s group have explored “out-of-autoclave,” or OoA, techniques to manufacture composites without using the huge machines. But most of these techniques have produced composites where nearly 1 percent of the material contains voids, which can compromise a material’s strength and lifetime. In comparison, aerospace-grade composites made in autoclaves are of such high quality that any voids they contain are neglible and not easily measured.

“The problem with these OoA approaches is also that the materials have been specially formulated, and none are qualified for primary structures such as wings and fuselages,” Wardle says. “They’re making some inroads in secondary structures, such as flaps and doors, but they still get voids.”

Straw pressure

Part of Wardle’s work focuses on developing nanoporous networks — ultrathin films made from aligned, microscopic material such as carbon nanotubes, that can be engineered with exceptional properties, including color, strength, and electrical capacity. The researchers wondered whether these nanoporous films could be used in place of giant autoclaves to squeeze out voids between two material layers, as unlikely as that may seem.

A thin film of carbon nanotubes is somewhat like a dense forest of trees, and the spaces between the trees can function like thin nanoscale tubes, or capillaries. A capillary such as a straw can generate pressure based on its geometry and its surface energy, or the material’s ability to attract liquids or other materials.

The researchers proposed that if a thin film of carbon nanotubes were sandwiched between two materials, then, as the materials were heated and softened, the capillaries between the carbon nanotubes should have a surface energy and geometry such that they would draw the materials in toward each other, rather than leaving a void between them. Lee calculated that the capillary pressure should be larger than the pressure applied by the autoclaves.

The researchers tested their idea in the lab by growing films of vertically aligned carbon nanotubes using a technique they previously developed, then laying the films between layers of materials that are typically used in the autoclave-based manufacturing of primary aircraft structures. They wrapped the layers in a second film of carbon nanotubes, which they applied an electric current to to heat it up. They observed that as the materials heated and softened in response, they were pulled into the capillaries of the intermediate CNT film.

The resulting composite lacked voids, similar to aerospace-grade composites that are produced in an autoclave. The researchers subjected the composites to strength tests, attempting to push the layers apart, the idea being that voids, if present, would allow the layers to separate more easily.

“In these tests, we found that our out-of-autoclave composite was just as strong as the gold-standard autoclave process composite used for primary aerospace structures,” Wardle says.

The team will next look for ways to scale up the pressure-generating CNT film. In their experiments, they worked with samples measuring several centimeters wide — large enough to demonstrate that nanoporous networks can pressurize materials and prevent voids from forming. To make this process viable for manufacturing entire wings and fuselages, researchers will have to find ways to manufacture CNT and other nanoporous films at a much larger scale.

“There are ways to make really large blankets of this stuff, and there’s continuous production of sheets, yarns, and rolls of material that can be incorporated in the process,” Wardle says.

He plans also to explore different formulations of nanoporous films, engineering capillaries of varying surface energies and geometries, to be able to pressurize and bond other high-performance materials.

“Now we have this new material solution that can provide on-demand pressure where you need it,” Wardle says. “Beyond airplanes, most of the composite production in the world is composite pipes, for water, gas, oil, all the things that go in and out of our lives. This could make making all those things, without the oven and autoclave infrastructure.”

This research was supported, in part, by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace Structures (NECST) Consortium.

“Affairs of the Heart” – Texas Heart Institute & Rice University – Damaged hearts are rewired with Nanotube Fibers

Researchers at Texas Heart Institute and Rice University have confirmed that flexible, conductive fibers made of carbon nanotubes can bridge damaged tissue to deliver electrical signals and keep hearts beating despite congestive heart failure or dilated cardiomyopathy or after a heart attack. @ Texas Heart Institute Thin, flexible fibers made of carbon nanotubes have now proven able to bridge damaged heart tissues and deliver the electrical signals needed to keep those hearts beating.

Scientists at Texas Heart Institute (THI) report they have used biocompatible fibers invented at Rice University in studies that showed sewing them directly into damaged tissue can restore electrical function to hearts.

“Instead of shocking and defibrillating, we are actually correcting diseased conduction of the largest major pumping chamber of the heart by creating a bridge to bypass and conduct over a scarred area of a damaged heart,” said Dr. Mehdi Razavi, a cardiologist and director of Electrophysiology Clinical Research and Innovations at THI, who co-led the study with Rice chemical and biomolecular engineer Matteo Pasquali.

“Today there is no technology that treats the underlying cause of the No. 1 cause of sudden death, ventricular arrhythmias,” Razavi said. “These arrhythmias are caused by the disorganized firing of impulses from the heart’s lower chambers and are challenging to treat in patients after a heart attack or with scarred heart tissue due to such other conditions as congestive heart failure or dilated cardiomyopathy.”

Results of the studies on preclinical models appear as an open-access Editor’s Pick in the American Heart Association’s Circulation: Arrhythmia and Electrophysiology. The association helped fund the research with a 2015 grant.

The research springs from the pioneering 2013 invention by Pasquali’s lab of a method to make conductive fibers out of carbon nanotubes. The lab’s first threadlike fibers were a quarter of the width of a human hair, but contained tens of millions of microscopic nanotubes. The fibers are also being studied for electrical interfaces with the brain, for use in cochlear implants, as flexible antennas and for automotive and aerospace applications.

The experiments showed the nontoxic, polymer-coated fibers, with their ends stripped to serve as electrodes, were effective in restoring function during month-long tests in large preclinical models as well as rodents, whether the initial conduction was slowed, severed or blocked, according to the researchers. The fibers served their purpose with or without the presence of a pacemaker, they found.

In the rodents, they wrote, conduction disappeared when the fibers were removed.

“The reestablishment of cardiac conduction with carbon nanotube fibers has the potential to revolutionize therapy for cardiac electrical disturbances, one of the most common causes of death in the United States,” said co-lead author Mark McCauley, who carried out many of the experiments as a postdoctoral fellow at THI. He is now an assistant professor of clinical medicine at the University of Illinois College of Medicine.

“Our experiments provided the first scientific support for using a synthetic material-based treatment rather than a drug to treat the leading cause of sudden death in the U.S. and many developing countries around the world,” Razavi added.

Many questions remain before the procedure can move toward human testing, Pasquali said. The researchers must establish a way to sew the fibers in place using a minimally invasive catheter, and make sure the fibers are strong and flexible enough to serve a constantly beating heart over the long term. He said they must also determine how long and wide fibers should be, precisely how much electricity they need to carry and how they would perform in the growing hearts of young patients.

“Flexibility is important because the heart is continuously pulsating and moving, so anything that’s attached to the heart’s surface is going to be deformed and flexed,” said Pasquali, who has appointments at Rice’s Brown School of Engineering and Wiess School of Natural Sciences.

“Good interfacial contact is also critical to pick up and deliver the electrical signal,” he said. “In the past, multiple materials had to be combined to attain both electrical conductivity and effective contacts. These fibers have both properties built in by design, which greatly simplifies device construction and lowers risks of long-term failure due to delamination of multiple layers or coatings.”

Razavi noted that while there are many effective antiarrhythmic drugs available, they are often contraindicated in patients after a heart attack. “What is really needed therapeutically is to increase conduction,” he said. “Carbon nanotube fibers have the conductive properties of metal but are flexible enough to allow us to navigate and deliver energy to a very specific area of a delicate, damaged heart.”

In Vivo Restoration of Myocardial Conduction With Carbon Nanotube Fibers

Mark D. McCauley, Flavia Vitale, J. Stephen Yan, Colin C. Young, Brian Greet, Marco Orecchioni, Srikanth Perike, Abdelmotagaly Elgalad, Julia A. Coco, Mathews John, Doris A. Taylor, Luiz C. Sampaio, Lucia G. Delogu, Mehdi Razavi, Matteo Pasquali

Circulation: Arrhythmia and Electrophysiology Vol. 12, No. 8

DOI: 10.1161/CIRCEP.119.007256

Contact information:

Matteo Pasquali

Professor of Chemical and Biomolecular Engineering at Rice University

mp@rice.edu

Phone: 713-348-5830

Pasquali Research Group

Mehdi Razavi

Cardiologist, Associate Professor of Medicine-Cardiology at Baylor College of Medicine and Director of Electrophysiology Clinical Research and Innovations at THI

razavi@bcm.edu

Rice University

Scientists develop Lithium Metal batteries that charge faster, last longer with 10X times more energy by volume than Li-Ion Batteries – BIG potential for Our EV / AV Future

 

October 25, 2018

Rice University scientists are counting on films of carbon nanotubes to make high-powered, fast-charging lithium metal batteries a logical replacement for common lithium-ion batteries.

The Rice lab of chemist James Tour showed thin nanotube films effectively stop dendrites that grow naturally from unprotected lithium metal anodes in batteries. Over time, these tentacle-like dendrites can pierce the battery’s electrolyte core and reach the cathode, causing the battery to fail.

That problem has both dampened the use of lithium metal in commercial applications and encouraged researchers worldwide to solve it.

Rice University graduate student Gladys López-Silva holds a lithium metal anode with a film of carbon nanotubes. Once the film is attached, it becomes infiltrated by lithium ions and turns red. Photo by Jeff Fitlow

Lithium metal charges much faster and holds about 10 times more energy by volume than the lithium-ion electrodes found in just about every electronic device, including cellphones and electric cars.

 

MIT NEWS: Read More About Lithium Metal Batteries

“One of the ways to slow dendrites in lithium-ion batteries is to limit how fast they charge,” Tour said. “People don’t like that. They want to be able to charge their batteries quickly.”

The Rice team’s answer, detailed in Advanced Materials, is simple, inexpensive and highly effective at stopping dendrite growth, Tour said.

“What we’ve done turns out to be really easy,” he said. “You just coat a lithium metal foil with a multiwalled carbon nanotube film. The lithium dopes the nanotube film, which turns from black to red, and the film in turn diffuses the lithium ions.”

“Physical contact with lithium metal reduces the nanotube film, but balances it by adding lithium ions,” said Rice postdoctoral researcher Rodrigo Salvatierra, co-lead author of the paper with graduate student Gladys López-Silva. “The ions distribute themselves throughout the nanotube film.”

An illustration shows how lithium metal anodes developed at Rice University are protected from dendrite growth by a film of carbon nanotubes. Courtesy of the Tour Group

When the battery is in use, the film discharges stored ions and the underlying lithium anode refills it, maintaining the film’s ability to stop dendrite growth.

The tangled-nanotube film effectively quenched dendrites over 580 charge/discharge cycles of a test battery with a sulfurized-carbon cathode the lab developed in previous experiments.

The researchers reported the full lithium metal cells retained 99.8 percent of their coulombic efficiency, the measure of how well electrons move within an electrochemical system.

Rice University scientists have discovered that a film of multiwalled carbon nanotubes quenches the growth of dendrites in lithium metal-based batteries. Courtesy of the Tour Group

Co-authors of the paper are Rice alumni Almaz Jalilov of the King Fahd University of Petroleum and Minerals, Saudi Arabia; Jongwon Yoon, a senior researcher at the Korea Basic Science Institute; and Gang Wu, an instructor, and Ah-Lim Tsai, a professor of hematology, both at the McGovern Medical School at the University of Texas Health Science Center at Houston.

Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.

The research was supported by the Air Force Office of Scientific Research, the National Institutes of Health, the National Council of Science and Technology, Mexico; the National Council for Scientific and Technological Development, Ministry of Science, Technology and Innovation and Coordination for the Improvement of Higher Education Personnel, Brazil; and Celgard, LLC.

Rice University chemist James Tour, left, graduate student Gladys López-Silva and postdoctoral researcher Rodrigo Salvatierra use a film of carbon nanotubes to prevent dendrite growth in lithium metal batteries, which charge faster and hold more power than current lithium-ion batteries. Photo by Jeff Fitlow.

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Using PEG Nanotubes as Drug Delivery Systems

This article is based around a talk given by Ben Newland from Cardiff University, UK, at the NANOMED conference hosted by the NANOSMAT Society in Manchester on the 26-28th June 2018. In his talk, Ben talks about how he uses soft and flexible poly(ethylene glycol) (PEG) nanotubes to provide a sustained and localized delivery of therapeutic drugs.

Link to Original AZ Nano Article

Dr. Newland, a lecturer at Cardiff University, has been dealing with PEG nanotubes for approximately ten years after they came about as a side project to his other research. It should be noted that these nanotubes are not like carbon nanotubes, in that they are not electronically confined in 2 dimensions (i.e., a 1D material), nor are they carbon nanotubes functionalized with PEG at the surface. They are strictly hollow cylinders that are made entirely of PEG, and only bear the name nanotube because that is what they most closely resemble (without the capped end).

The research came about after previously working on carbon nanopipes, where a porous template was used to create hollow carbon nanostructures; in conjunction with another area of Ben’s research, which looks at using cyclized knotted polymers as drug delivery agents. To combine these areas, Ben poured a polymer solution (with a photo-initiator) into a porous template and shone UV light on it, which in turn cross-linked the polymers and created tube-like structures. This was the starting point of this research.

Since starting the research, Ben has incrementally polished the process and now produces polymer nanotubes which are 200 nm in diameter and up to 60 micrometers in length. Cyclized knot polymers are required to construct these nanotubes and can be made with commercially available PEG materials that contain di-vinyl groups. Different polymers have been trialed, and the PEG nanotubes were found to be the softest.

The possibility of using these for drug delivery applications came about after they were found to uptake rhodamine (a tracer dye). On the process side, Ben’s research team discovered that when the templates are dissolved (with sodium hydroxide) to leave just the nanotubes, the process breaks some of the ester bonds and creates an abundance of negative charges on the surface of the nanotubes.

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The anti-cancer drug, doxorubicin, was also found to be actively uptaken out of solution by the negatively charged nanotubes, and it is a straightforward procedure to determine the uptake and release of doxorubicin as it is intrinsically fluorescent and has a colored appearance. Ben’s work has led him to look at the release of doxorubicin from the nanotubes and found that they release most of the drug payload within the first five days, but there is a sustained delivery of 2-3 micrograms over 35 to 40 days. Some of the doxorubicin was found to stay in the nanotube, so while it is not perfect at the moment regarding the release, these nanotubes do show a lot of promise as new material as drug delivery agents.

One aspect of any delivery agent is that it needs to be biocompatible and low in cytotoxicity. In-vitro cell viability tests have been performed for these nanotubes at varying concentrations, and up to the point where the nanotubes are completely covering the cell. The results showed that even at the end (fully covered cells) the nanotubes did not kill the cell. Other cell viability studies on drug-loaded nanotubes found that the release of the drugs was killing the cells, and thus confirmed its position as a potential drug delivery agent.

The research has been taken further and has been tested on metastatic breast cancer cells in mice in conjunction with researchers from the University of Strathclyde. These studies have shown that the doxorubicin-loaded nanotubes reduced the tumor growth and reduced metastasis (the creation of secondary tumors away from the primary tumor site) in the mice.

Future studies will look at the cytotoxicity of the polymer nanotubes in-vivo and will look at how the drug release profile can be improved. Other areas will look at varying the size of the nanotubes, changing the chain length to alter the stiffness and entanglement of the nanotubes and looking at the effects of functionalizing the nanotubes with different nanoparticles.

Sources:

• NANOMED 2018: http://www.nanomed.uk.com/

• Ben Newland: http://www.newlandresearch.net/

Rice University: Nanotubes change the shape of water

Molecular models of nanotube ice produced by engineers at Rice University show how forces inside a carbon nanotube at left and a boron nitride nanotube at right pressure water molecules into taking on the shape of a square tube. The …more

First, according to Rice University engineers, get a nanotube hole. Then insert water. If the nanotube is just the right width, the water molecules will align into a square rod.

Rice materials scientist Rouzbeh Shahsavari and his team used molecular models to demonstrate their theory that weak van der Waals forces between the inner surface of the nanotube and the water molecules are strong enough to snap the oxygen and hydrogen atoms into place.

Shahsavari referred to the contents as two-dimensional “ice,” because the molecules freeze regardless of the temperature. He said the research provides valuable insight on ways to leverage atomic interactions between nanotubes and water molecules to fabricate nanochannels and energy-storing nanocapacitors.

A paper on the research appears in the American Chemical Society journal Langmuir.

Shahsavari and his colleagues built molecular models of carbon and boron nitride nanotubes with adjustable widths. They discovered boron nitride is best at constraining the shape of water when the nanotubes are 10.5 angstroms wide. (One angstrom is one hundred-millionth of a centimeter.)

The researchers already knew that hydrogen atoms in tightly confined water take on interesting structural properties. Recent experiments by other labs showed strong evidence for the formation of nanotube ice and prompted the researchers to build density functional theory models to analyze the forces responsible.

Shahsavari’s team modeled water molecules, which are about 3 angstroms wide, inside carbon and boron nitride nanotubes of various chiralities (the angles of their atomic lattices) and between 8 and 12 angstroms in diameter. They discovered that nanotubes in the middle diameters had the most impact on the balance between molecular interactions and van der Waals pressure that prompted the transition from a square water tube to ice.

“If the nanotube is too small and you can only fit one water molecule, you can’t judge much,” Shahsavari said. “If it’s too large, the water keeps its amorphous shape. But at about 8 angstroms, the nanotubes’ van der Waals force starts to push water molecules into organized square shapes.”

He said the strongest interactions were found in boron nitride nanotubes due to the particular polarization of their atoms.

Shahsavari said nanotube ice could find use in molecular machines or as nanoscale capillaries, or foster ways to deliver a few molecules of water or sequestered drugs to targeted cells, like a nanoscale syringe.

 Explore further: Scientists say boron nitride-graphene hybrid may be right for next-gen green cars

More information: Farzaneh Shayeganfar et al, First Principles Study of Water Nanotubes Captured Inside Carbon/Boron Nitride Nanotubes, Langmuir (2018). DOI: 10.1021/acs.langmuir.8b00856

Journal reference: Langmuir  

Provided by: Rice University

Rice U: New Lithium metal battery prototype boasts 3X the capacity of current lithium-ions ~ Dendrite Problem Solved?

Could a new material involving a carbon nanotube and graphene hybrid put an end to the dendrite problem in lithium batteries? (Credit: Tour Group/Rice University)

The high energy capacity of lithium-ion batteries has led to them powering everything from tiny mobile devices to huge trucks. But current lithium-ion battery technology is nearing its limits and the search is on for a better lithium battery. But one thing stands in the way: dendrites. If a new technology by Rice University scientists lives up to its potential, it could solve this problem and enable lithium-metal batteries that can hold three times the energy of lithium-ion ones.

Dendrites are microscopic lithium fibers that form on the anodes during the charging process, spreading like a rash till they reach the other electrode and causing the battery to short circuit. As companies such as Samsung know only too well, this can cause the battery to catch fire or even explode.

“Lithium-ion batteries have changed the world, no doubt,” says chemist Dr. James Tour, who led the study. “But they’re about as good as they’re going to get. Your cellphone’s battery won’t last any longer until new technology comes along.”

So until scientists can figure out a way to solve the problem of dendrites, we’ll have to put our hopes for a higher capacity, faster-charging battery that can quell range anxiety on hold. This explains why there’s been no shortage of attempts to solve this problem, from using Kevlar to slow down dendrite growth to creating a new electrolyte that could lead to the development of an anode-free cell. So how does this new technology from Rice University compare?

For a start, it’s able to stop dendrite growth in its tracks. Key to it is a unique anode made from a material that was first created at the university five years ago. By using a covalent bond structure, it combines a two-dimensional graphene sheet and carbon nanotubes to form a seamless three-dimensional structure. As Tour explained back when the material was first unveiled:

“By growing graphene on metal (in this case copper) and then growing nanotubes from the graphene, the electrical contact between the nanotubes and the metal electrode is ohmic. That means electrons see no difference, because it’s all one seamless material.”

Close-up of the lithium metal coating the graphene-nanotube anode (Credit: Tour Group/Rice University)

 

Envisioned for use in energy storage and electronics applications such as supercapacitors, it wasn’t until 2014, when co-lead author Abdul-Rahman Raji was experimenting with lithium metal and the graphene-nanotube hybrid, that the researchers discovered its potential as a dendrite inhibitor.

“I reasoned that lithium metal must have plated on the electrode while analyzing results of experiments carried out to store lithium ions in the anode material combined with a lithium cobalt oxide cathode in a full cell,” says Raji. “We were excited because the voltage profile of the full cell was very flat. At that moment, we knew we had found something special.”

Closer analysis revealed no dendrites had grown when the lithium metal was deposited into a standalone hybrid anode – but would it work in a proper battery?

To test the anode, the researchers built full battery prototypes with sulfur-based cathodes that retained 80 percent capacity after more than 500 charge-discharge cycles (i.e. the rough equivalent of what a cellphone goes through in a two-year period). No signs of dendrites were observed on the anodes.

How it works

The low density and high surface area of the nanotube forest allow the lithium metal to coat the carbon hybrid material evenly when the battery is charged. And since there is plenty of space for the particles to slip in and out during the charge and discharge cycle, they end up being evenly distributed and this stops the growth of dendrites altogether.

According to the study, the anode material is capable of a lithium storage capacity of 3,351 milliamp hours per gram, which is close to pure lithium’s theoretical maximum of 3,860 milliamp hours per gram, and 10 times that of lithium-ion batteries. And since the nanotube carpet has a low density, this means it’s able to coat all the way down to substrate and maximize use of the available volume.

“Many people doing battery research only make the anode, because to do the whole package is much harder,” says Tour. “We had to develop a commensurate cathode technology based upon sulfur to accommodate these ultrahigh-capacity lithium anodes in first-generation systems. We’re producing these full batteries, cathode plus anode, on a pilot scale, and they’re being tested.”

The study was published in ACS Nano.

Source: Rice University

 

Creating a Life-Saving, Blood-Repellent Super Material – Revolutionizing Medical Implants: Colorado State University

Briefly

• Biomedical engineers and materials scientists have developed a “superhemophobic” surface treatment for titanium that repels liquids including blood, plasma, and water.
• The result is a surface that completely repels any liquid with which it would come in contact – a material that could revolutionize medical implants.

GOODBYE REJECTION

Implanted medical devices like stents, catheters, and titanium rods are essential, life-saving tools for patients around the world. Still, having a foreign object in the human body does pose its own risks – chiefly, having the body reject the object or increasing the risk of dangerous blood clots. A new collaboration between two distinct scientific disciplines is working toward making those risks a concern of the past.

Biomedical engineers and materials scientists from Colorado State University (CSU) have developed a “superhemophobic” surface treatment for titanium that repels liquids including blood, plasma, and water. The titanium is essentially studded with nanoscale tubes treated with a non-stick chemical. The result is a surface that completely repels any liquid with which it would come in contact. The team’s findings are published in Advanced Healthcare Materials.

Fluorinated nanotubes provided the best superhemophobic surfaces in the CSU researchers’ experiments. Credit: Kota lab/Colorado State University

AN END TO CLOTTING

In cases where a body does reject a medical implant, the patient’s immune system detects the foreign object and mounts a defense against it, which can lead to serious inflammation and other complications. The real trick to the team’s surface is that the body doesn’t even recognize that it’s there. According to Arun Kota, assistant professor of mechanical engineering and biomedical engineering at CSU, “We are taking a material that blood hates to come in contact with, in order to make it compatible with blood.”

Regarding clotting, patients with medical implants often need to stay on a regimen of blood-thinning drugs to decrease the risk. However, blood thinners are not guaranteed to work, and they also carry the risk of leading to excessive bleeding due to the prevention of even beneficial clotting near wounds. As Ketul Popat, associate professor of mechanical engineering and biomedical engineering at CSU explains, “The reason blood clots is because it finds cells in the blood to go to and attach.” He continues, “if we can design materials where blood barely contacts the surface, there is virtually no chance of clotting.”

This material is only in its earliest stages of development. Should the team’s findings hold up to further scrutinization, these life-saving medical devices could be given an unprecedented boost in safety.

References: Advanced Healthcare Materials. 

Kota Labs Research Group: Colorado State University