Nanofibers twisted together to create structures tougher than bullet proof vests


Researchers at the University of Texas at Dallas have created new structures that exploit the electromechanical properties of specific nanofibers to stretch to up to seven times their length, while remaining tougher than Kevlar.

Testing-the-Bullet-Proof-Vest

The Science and the Materials have come a very long way!
These structures absorb up to 98 joules per gram. Kevlar, often used to make bulletproof vests, can absorb up to 80 joules per gram. The material can reinforce itself at points of high stress and could potentially be used in military airplanes or other defense applications.

In a study published by ACS Applied Materials and Interfaces, a journal of the American Chemical Society, researchers twisted nanofiber into yarns and coils. The electricity generated by stretching the twisted nanofiber formed an attraction 10 times stronger than a hydrogen bond, which is considered one of the strongest forces formed between molecules.

Nano Fibers BP Vest 032715 150326112338-large

Dr. Majid Minary, an assistant professor of mechanical engineering, was senior author of the study.
Credit: Image courtesy of University of Texas, Dallas

Researchers sought to mimic their earlier work on the piezoelectric action (how pressure forms electric charges) of collagen fibers found inside bone in hopes of creating high-performance materials that can reinforce itself, said Dr. Majid Minary, an assistant professor of mechanical engineering in UT Dallas’ Erik Jonsson School of Engineering and Computer Science and senior author of the study.

“We reproduced this process in nanofibers by manipulating the creation of electric charges to result in a lightweight, flexible, yet strong material,” said Minary, who is also a member of the Alan G. MacDiarmid NanoTech Institute. “Our country needs such materials on a large scale for industrial and defense applications.”

For their experiment, researchers first spun nanofibers out of a material known as polyvinylidene fluoride (PVDF) and its co-polymer, polyvinvylidene fluoride trifluoroethylene (PVDF-TrFE).

Researchers then twisted the fibers into yarns, and then continued to twist the material into coils.

“It’s literally twisting, the same basic process used in making conventional cable,” Minary said.

Researchers then measured mechanical properties of the yarn and coils such as how far it can stretch and how much energy it can absorb before failure.

“Our experiment is proof of the concept that our structures can absorb more energy before failure than the materials conventionally used in bulletproof armors,” Minary said. “We believe, modeled after the human bone, that this flexibility and strength comes from the electricity that occurs when these nanofibers are twisted.”

The next step in the research is to make larger structures out of the yarns and coils, Minary said.

Other UT Dallas authors on the paper are Mahmoud Baniasadi, Zhe Xu, Yang Xi and Salvador Moreno, all research assistants in the Jonsson School; alumnus Jiacheng Huang; Jason Chang, a biomedical engineering senior; and Dr. Manuel Quevedo-Lopez, professor of materials science and engineering. Dr. Mohammad Naraghi, an assistant professor of aerospace engineering at Texas A&M University, also participated in the work.

The work was funded by the Air Force Office of Scientific Research Young Investigator Research Programand the National Science Foundation.


Story Source:

The above story is based on materials provided by University of Texas, Dallas. Note: Materials may be edited for content and length.

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Genesis Nanotech Headlines Are Out!


Organ on a chip organx250Genesis Nanotech Headlines Are Out! Read All About It!

https://paper.li/GenesisNanoTech/1354215819#!headlines

Visit Our Website: www.genesisnanotech.com

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SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DCThe Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

electron-tomography

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Stronger, Lighter, Less Expensive than Kevlar: New Carbon Nanotube Technology


minus600-590x393Place two large, sturdy logs in a streambed, and they will help guide the water in a par­tic­ular direc­tion. But imagine if the water started mim­ic­king the rigidity of the logs in addi­tion to flowing along them. That’s essen­tially what hap­pens in a directed assembly method devel­oped by Mar­ilyn Minus, an assis­tant pro­fessor in Northeastern’s Depart­ment of Mechan­ical and Indus­trial Engi­neering.

Instead of logs, Minus uses tiny carbon nan­otubes and her “water” can be just about any kind of polymer solu­tion. So far, she’s used the approach to develop a polymer com­posite mate­rial that is stronger than Kevlar yet much less expen­sive and lighter weight. In that case, the polymer not only fol­lows the direc­tion of the nan­otube logs but also mimics their uniquely strong properties.

With funding from a new CAREER award from the National Sci­ence Foun­da­tion, Minus is now expanding this work to incor­po­rate more polymer classes: flame retar­dant mate­rials and bio­log­ical molecules.

minus600-590x393

Assistant professor Marilyn Minus has received a grant to expand her nanomaterial templating process to design better synthetic collagen fibers and better flame-retardant coatings. Photo by Mary Knox Merrill.

With the flame retar­dants, we want the high-​​temperature polymer and nan­otube to interact, not nec­es­sarily act like the nan­otubes,” Minus said. Essen­tially, she wants the two mate­rials to “com­mu­ni­cate” by passing heat between one another, thereby increasing the tem­per­a­ture threshold of the flame retar­dants and allowing them to last even longer. “The nano­ma­te­rial can grab that heat and con­duct it away, and it basi­cally saves that polymer from burning up too quickly,” she explained. “The polymer we’re using can already with­stand quite high tem­per­a­tures; we’re just pushing it even further.”

In the case of collagen—the first bio­log­ical mol­e­cule to which Minus has applied her method—Minus hopes the approach will allow the nan­otubes to lend their rigidity to the system. Inside the body, col­lagen mol­e­cules orga­nize them­selves into a com­plex matrix that sup­ports the struc­ture of every one of our cells. But out­side the body, researchers have had major chal­lenges trying to reli­ably recreate this matrix.

If sci­en­tists could make col­lagen work out­side the body the same way it does inside, it could pro­vide an invalu­able plat­form for testing drugs, under­standing how tis­sues work, and even shed­ding light on the ori­gins of a variety of dis­eases, Minus said.

Based on her prior research, she has found that the key to suc­cess in taking this approach is matching the size and geom­etry of the carbon nanopar­ti­cles she uses with that of the polymer in ques­tion. For instance, col­lagen mol­e­cules are about 300 nanome­ters long and 1.5 nanome­ters in diam­eter, so she’ll want to find a nan­otube that roughly meets those dimen­sions. She’ll also want to use nan­otubes for this appli­ca­tion rather than the other carbon forms she has at her dis­posal: graphene, graphite, fullerenes, or even small nanocarbon particles—each of which offers a unique structure.

We’re trying to change the entropy of the system in order to get the poly­mers to orga­nize them­selves around the nano­ma­te­rials,” Minus said. “Then you should be able to get this effect.”

Making Nano-Fibers Affordable


QDOTS imagesCAKXSY1K 8Nanofibers — strands of material only a couple hundred nanometers in diameter — have a huge range of possible applications: scaffolds for bioengineered organs, ultrafine air and water filters, and lightweight Kevlar body armor, to name just a few. But so far, the expense of producing them has consigned them to a few high-end, niche applications.
Luis Velásquez-García, a principal research scientist at MIT’s Microsystems Technology Laboratories, and his group hope to change that. At the International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications in December, Velásquez-García, his student Philip Ponce de Leon, and Frances Hill, a postdoc in his group, will describe a new system for spinning nanofibers that should offer significant productivity increases while drastically reducing power consumption.
Using manufacturing techniques common in the microchip industry, the MTL researchers built a one-square-centimeter array of conical tips, which they immersed in a fluid containing a dissolved plastic. They then applied a voltage to the array, producing an electrostatic field that is strongest at the tips of the cones. In a technique known as electrospinning, the cones eject the dissolved plastic as a stream that solidifies into a fiber only 220 nanometers across.

In their experiments, the researchers used a five-by-five array of cones, which already yields a sevenfold increase in productivity per square centimeter over even the best existing methods. But, Velásquez-García says, it should be relatively simple to pack more cones onto a chip, boosting productivity even more. Indeed, he says, in prior work on a similar technique called electrospray, his lab was able to cram almost a thousand emitters into a single square centimeter. And multiple arrays could be combined in a panel to further increase yields.

Surfaces, from scratch
Because the new paper was prepared for an energy conference, it focuses on energy applications. But nanofibers could be useful for any device that needs to maximize the ratio of surface area to volume, Velásquez-García says. Capacitors — circuit components that store electricity — are one example, because capacitance scales with surface area. The electrodes used in fuel cells are another, because the greater the electrodes’ surface area, the more efficiently they catalyze the reactions that drive the cell. But almost any chemical process can benefit from increasing catalysts’ surface area, and increasing the surface area of artificial-organ scaffolds gives cells more points at which to adhere.

Watch the Video Here: http://youtu.be/eWGPW1tS38U

Another promising application of nanofibers is in meshes so fine that they allow only nanoscale particles to pass through. The example in the new paper again comes from energy research: the membranes that separate the halves of a fuel cell. But similar meshes could be used to filter water. Such applications, Velásquez-García says, depend crucially on consistency in the fiber diameter, another respect in which the new technique offers advantages over its predecessors.

Existing electrospinning techniques generally rely on tiny nozzles, through which the dissolved polymer is forced. Variations in operating conditions and in the shape of the nozzles can cause large variation in the fiber diameter, and the nozzles’ hydraulics mean that they can’t be packed as tightly together. A few manufacturers have developed fiber-spinning devices that use electrostatic fields, but their emitters are made using much cruder processes than the chip-manufacturing techniques that the MTL researchers exploited. As a consequence, not only are the arrays of tips much less dense, but the devices consume more power.
“The electrostatic field is enhanced if the tip diameter is smaller,” Velásquez-García says. “If you have tips of, say, millimeter diameter, then if you apply enough voltage, you can trigger the ionization of the liquid and spin fibers. But if you can make them sharper, then you need a lot less voltage to achieve the same result.”

Wicked wicker
The use of microfabrication technologies not only allowed the MTL researchers to pack their cones more tightly and sharpen their tips, but it also gave them much more precise control of the structure of the cones’ surfaces. Indeed, the sides of the cones have a nubby texture that helps the cones wick up the fluid in which the polymer is dissolved. In ongoing experiments, the researchers have also covered the cones with what Velásquez-García describes as a “wool” of carbon nanotubes, which should work better with some types of materials.

Indeed, Velásquez-García says, his group’s results depend not only on the design of the emitters themselves, but on a precise balance between the structure of the cones and their textured coating, the strength of the electrostatic field, and the composition of the fluid bath in which the cones are immersed.
“Fabricating exactly identical emitters in parallel with high precision and a lot of throughput — this is their main contribution, in my opinion,” says Antonio Luque Estepa, an associate professor of electrical engineering at the University of Seville who specializes in electrospray deposition and electrospinning.

“Fabricating one is easy. But 100 or 1,000 of them, that’s not so easy. Many times there are problems with interactions between one output and the output next to it.”

The microfabrication technique that Velásquez-García’s group employs, Luque adds, “does not limit the number of outputs that they can integrate on one chip.” Although the extent to which the group can increase emitter density remains to be seen, Luque says, he’s confident that “they can make a tenfold increase over what is available right now.”

The MIT researchers’ work was funded in part by the U.S. Defense Advanced Research Projects Agency.

MIT News: Making ‘nanospinning’ practical


Spinning nanofibers Nanofibers have a dizzying range of possible applications, but they’ve been prohibitively expensive to make. MIT researchers hope to change that.

Nanofibers — strands of material only a couple hundred nanometers in diameter — have a huge range of possible applications: scaffolds for bioengineered organs, ultrafine air and water filters, and lightweight Kevlar body armor, to name just a few. But so far, the expense of producing them has consigned them to a few high-end, niche applications.

Luis Velásquez-García, a principal research scientist at MIT’s Microsystems Technology Laboratories, and his group hope to change that. At the International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications in December, Velásquez-García, his student Philip Ponce de Leon, and Frances Hill, a postdoc in his group, will describe a new system for spinning nanofibers that should offer significant productivity increases while drastically reducing power consumption.

Using manufacturing techniques common in the microchip industry, the MTL researchers built a one-square-centimeter array of conical tips, which they immersed in a fluid containing a dissolved plastic. They then applied a voltage to the array, producing an electrostatic field that is strongest at the tips of the cones. In a technique known as electrospinning, the cones eject the dissolved plastic as a stream that solidifies into a fiber only 220 nanometers across.

In their experiments, the researchers used a five-by-five array of cones, which already yields a sevenfold increase in productivity per square centimeter over even the best existing methods. But, Velásquez-García says, it should be relatively simple to pack more cones onto a chip, boosting productivity even more. Indeed, he says, in prior work on a similar technique called electrospray, his lab was able to cram almost a thousand emitters into a single square centimeter. And multiple arrays could be combined in a panel to further increase yields.

Surfaces, from scratch

Because the new paper was prepared for an energy conference, it focuses on energy applications. But nanofibers could be useful for any device that needs to maximize the ratio of surface area to volume, Velásquez-García says. Capacitors — circuit components that store electricity — are one example, because capacitance scales with surface area. The electrodes used in fuel cells are another, because the greater the electrodes’ surface area, the more efficiently they catalyze the reactions that drive the cell. But almost any chemical process can benefit from increasing catalysts’ surface area, and increasing the surface area of artificial-organ scaffolds gives cells more points at which to adhere.

Watch YouTube Video from MIT on Nanofibers here:

Another promising application of nanofibers is in meshes so fine that they allow only nanoscale particles to pass through. The example in the new paper again comes from energy research: the membranes that separate the halves of a fuel cell. But similar meshes could be used to filter water. Such applications, Velásquez-García says, depend crucially on consistency in the fiber diameter, another respect in which the new technique offers advantages over its predecessors.

Existing electrospinning techniques generally rely on tiny nozzles, through which the dissolved polymer is forced. Variations in operating conditions and in the shape of the nozzles can cause large variation in the fiber diameter, and the nozzles’ hydraulics mean that they can’t be packed as tightly together. A few manufacturers have developed fiber-spinning devices that use electrostatic fields, but their emitters are made using much cruder processes than the chip-manufacturing techniques that the MTL researchers exploited. As a consequence, not only are the arrays of tips much less dense, but the devices consume more power.

“The electrostatic field is enhanced if the tip diameter is smaller,” Velásquez-García says. “If you have tips of, say, millimeter diameter, then if you apply enough voltage, you can trigger the ionization of the liquid and spin fibers. But if you can make them sharper, then you need a lot less voltage to achieve the same result.”

Wicked wicker

The use of microfabrication technologies not only allowed the MTL researchers to pack their cones more tightly and sharpen their tips, but it also gave them much more precise control of the structure of the cones’ surfaces. Indeed, the sides of the cones have a nubby texture that helps the cones wick up the fluid in which the polymer is dissolved. In ongoing experiments, the researchers have also covered the cones with what Velásquez-García describes as a “wool” of carbon nanotubes, which should work better with some types of materials.

Indeed, Velásquez-García says, his group’s results depend not only on the design of the emitters themselves, but on a precise balance between the structure of the cones and their textured coating, the strength of the electrostatic field, and the composition of the fluid bath in which the cones are immersed.

“Fabricating exactly identical emitters in parallel with high precision and a lot of throughput — this is their main contribution, in my opinion,” says Antonio Luque Estepa, an associate professor of electrical engineering at the University of Seville who specializes in electrospray deposition and electrospinning. “Fabricating one is easy. But 100 or 1,000 of them, that’s not so easy. Many times there are problems with interactions between one output and the output next to it.”

The microfabrication technique that Velásquez-García’s group employs, Luque adds, “does not limit the number of outputs that they can integrate on one chip.” Although the extent to which the group can increase emitter density remains to be seen, Luque says, he’s confident that “they can make a tenfold increase over what is available right now.”

The MIT researchers’ work was funded in part by the U.S. Defense Advanced Research Projects Agency.