Tag Archives: polymer

N. aromaticivorans bacteria.

Slightly-tweaked microbe could create plastics from a common plant waste material

A few genetic modifications can induce a strain of soil bacteria to convert a renewable material, lignin, into plastics. The best part? Lignin is so cheap and plentiful we don’t even bother trying to use it right now.

N. aromaticivorans bacteria.

N. aromaticivorans bacteria.
Image credits Great Lakes Bioenergy Research Center / UoW.

Woody plants show great promise as a potential replacement for petroleum in various uses — such as fuel, plastics, and chemical production. They contain a lot of sugars, which can be used for those applications, but they’re kept out of reach behind the cellulose in their cellular walls.

Those walls are so durable and hard (read: ‘expensive’) to break down industrially, that we generally don’t really bother extracting the materials.

Mister bacteria, break down this wall

A team of researchers at the Great Lakes Bioenergy Research Center (based at the University of Wisconsin-Madison-based and funded by the Department of Energy) hopes that a bacteria species can point the way to woody-plants-based replacements for petroleum. Their plan is to take this microscopic critter, tweak its genome around a bit, and unleash it on the plants’ cells — where it will transform all the lignin, a polymer that ties cellulose to the sugars, into something we can actually use.

Lignin is actually super abundant. It’s the second-most abundant type of aromatic compound (those ‘rings’ you see in organic chemistry) on the planet after petroleum, the team explains. However, isn’t very valuable right now. That’s actually an understatement. Lignin today is so cheap that paper mills — which have been in the business of stripping lignin from wood for centuries — can’t even bother trying to sell the stuff; they just dispose of it in huge boilers.

“They say you can make anything from lignin except money,” says Miguel Perez, a UW-Madison graduate student in civil and environmental engineering and the paper’s first author.

The bacteria in question is Novosphingobium aromaticivorans. It was first isolated in soils that were previously contaminated by petroleum products. And, in this environment where most other organisms find it hard to eek out a living, N. aromaticivorans was thriving. Its name aromaticivorans means ‘aromatic-eater’ as a nod to its unique adaptations.

Lignin is a large molecule that’s very difficult to break down into smaller pieces. But N. aromaticivorans already had a natural appetite for lignin-like products when discovered — in fact, it’s the only known organism so far that can digest many parts of the lignin molecule and excrete smaller aromatic compounds.

“Other microbes tried before may be able to digest a few types of aromatics found in lignin,” Perez says. “When we met this microbe, it was already good at degrading a wide range of compounds. That makes this microbe very promising.”

During this process, N. aromaticivorans produces 2-pyrone-4,6-dicarboxylic acid or PDC. The team engineered the bacteria by removing three genes in its genome, further stabilizing the digestion process and coaxing it reducing all its meal into PDC. In the end, what they obtained was an organism which could be fed any part of the lignin molecule and produce PDC.

“There’s no industrial process for doing that, because PDC is so difficult to make by existing routes,” says Daniel Noguera, the study’s corresponding author. “But if we’re making biofuels from cellulose and producing lignin — something we used to just burn — and we can efficiently turn the lignin into PDC, that potentially changes the market for industrial use of this compound.”

“The compound performs the same or better than the most common petroleum-based additive to PET polymers — like plastic bottles and synthetic fibers — which are the most common polymers being produced in the world,” Perez adds.

PDC is also biodegradable and doesn’t leach any by-products while it degrades.

For now, the engineered variation on N. aromaticivorans can turn at least 59% of lignin’s potentially useful compounds into PDC. The team suggests that a greater efficiency is possible through further genetic manipulation of the microbe. They’re currently at work implementing such changes and “might create a new industry,” Noguera says.

The paper “Funneling aromatic products of chemically depolymerized lignin into 2-pyrone-4-6-dicarboxylic acid with Novosphingobium aromaticivorans” has been published in the journal Green Chemistry.

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

Polymer paint passively cools down any surface

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

Heat-waves are on the rise all over the world, becoming more frequent and more intense. Developing countries are the hardest hit: not only are heat waves more extreme than in other parts of the world but cooling methods are also more difficult to implement due to cost. In such situations, passive cooling — which doesn’t require electricity or any kind of energy input — is the way to go.

Plastics and other cheap polymers are actually excellent heat radiators, which would make them ideal for passive daytime radiative cooling (PDRC) if scientists could figure out how to get these normally transparent surfaces to reflect sunlight without using silver mirrors.

Researchers at Columbia University have finally been able to accomplish this. Reporting in the journal Science, the authors described a PDRC polymer coating with nano- and micro-scale voids that act as passive air coolers. The amazing part is that the coating can be applied like paint on rooftops, buildings, vehicles — basically anything.

Apply and cool

A passive cooling surface is effective when it has a high solar reflectance and emittance. In other words, if these two variables are high enough, there’s a net heat loss effect ever under intense sunlight.

The cheapest and, often times, most practical PDRC is white paint. If you’ve ever switched a black shirt for a white shirt on a hot summer day, you must know how much of a difference this can make.

The problem with white paint, however, is that it doesn’t reflect longer wavelengths of light, so its cooling performance is modest.

Passive daytime radiative cooling (PDRC) works by reflecting sunlight and emitting heat in order to achieve a net heat loss. This way, a surface can attain sub-ambient temperatures. Credit: Jyotirmoy Mandal.

Passive daytime radiative cooling (PDRC) works by reflecting sunlight and emitting heat in order to achieve a net heat loss. This way, a surface can attain sub-ambient temperatures. Credit: Jyotirmoy Mandal.

Using phase-inversion, the Columbia Engineering team was able to introduce light-scattering air-voids in polymers. The process involved mixing the polymer with a solvent alongside water, in which the polymer is insoluble. Ultimately, the pigments in white paint were replaced with air voids that reflect all wavelengths of light, from UV to infrared. And even though there were no pigments, the polymer still turned white.

What you get is a far better performance than typical white paint and even better than some state-of-the-art PDRCs that are complex and costly. What’s more, there’s the convenience that the polymer coating can be applied like paint to virtually any surface.

During tests, the coating kept surfaces significantly cooler than the surrounding environment under widely different skies. For instance, the polymer paint cooled surfaces by 6°C in the warm, arid desert in Arizona and 3°C in the foggy, tropical environment of Bangladesh.

Another selling point is stability. For instance, cellulose, which is the main component of paper, turns yellow over time. The porous films developed at Columbia, however, did not seem to change one bit over the course of a month in the field.

“The fact that cooling is achieved in both desert and tropical climates, without any thermal protection or shielding, demonstrates the utility of our design wherever cooling is required,” Yuan Yang, assistant professor of materials science and engineering, said in a statement.

“Now is a critical time to develop promising solutions for sustainable humanity,” Yang added, “This year, we witnessed heat waves and record-breaking temperatures in North America, Europe, Asia, and Australia. It is essential that we find solutions to this climate challenge, and we are very excited to be working on this new technology that addresses it.”

Until not too long ago, white was thought to be the most challenging color to manufacture. The new research, however, shows that, in fact, white can be the most attainable color.

“It can be made using nothing more than properly sized air voids embedded in a transparent medium. Air voids are what make snow white and Saharan silver ants silvery,” Nanfang Yu, associate professor of applied physics said in a statement.

Rheometer with material.

Novel material can change under the right light, to be either strong or self-healing

A new MIT-designed polymer can both put up a tough front or show its softer side and heal — its mood changes with the ambient light.

Rheometer with material.

A rheometer, a device used to measure the mechanical properties of materials. The blue-colored gel on the stage of the instrument is the material developed by MIT.
Image credits Felice Frankel.

Materials have come a long way. Far gone are the days when we only had stones for tools and pelts to dress with — now we have fancy things like plastics, glass, metals or concrete to shape our world with. We’re also much better at processing them with high precision, which took us from shaky beds and tough-spun tunics to comfy, modern beds and comfy, modern clothing.

However, for all our advances in material science, we’ve yet to develop something that’s resilient without requiring occasional repairs. Since mending is tedious, boring, and occasionally impossible (think of a satellite in orbit), one research team from MIT decided to develop a material that takes care of that problem.

Researchers have dabbled in self-healing materials before. These efforts haven’t yet seen wide-scale applications, but they’re not exactly ‘new’ either. However, self-healing materials tend to trade resilience for their ability to repair themselves. What this new research brings to the table is a material that can be both hardy and self-healing — I say ‘both’ but it’s more of a case of ‘either/or’.

Light healing

A material’s structural strength stems from the way its constituent atoms and molecules tie to one another — a characteristic known as a material’s ‘topology’. Self-healing materials need a laxer topology with more permissive bonds in order to ebb and flow into any damaged areas. However, that also makes the end material much less resilient — which is a product of a rigid, well-knit topology.

To work around the problem, the team designed a polymer that can actually change its own topology in response to light.

“You can switch the material states back and forth, and in each of those states, the material acts as though it were a completely different material, even though it’s made of all the same components,” says Jeremiah Johnson, an associate professor of chemistry at MIT, and lead researcher of the project.

Topology is something that typically remains fixed after a material is formed. Or, if this topology is altered, it’s usually not via a reversible process. Rubber, for example, becomes brittle over time due to ozonation and oxidation (reactions with ozone and oxygen, respectively), which alter its topology.

To make the process reversible, the team worked with polymers attached to photosensitive molecules. This way, they could use light to activate and change the topology of the material.

PolyMOCs.

The design of polyMOCs with photoswitchable topology.
Image and caption credits: Yuwei Gu et al., 2018, Nature.

The team started from a class of materials they had designed previously, known as polymer metal-organic cages — or polyMOCs. The researchers describe them as metal-containing cage-like structures strewn together by flexible polymer bridges. The metal bits of the material are tied to the strands of polymer using chemical structures called ligands. Each metal atom (the team used palladium) can bind to four ligand molecules, and several of these sub-assemblies come together to create a rigid structure (the ‘cages’). The exact ratio of ligand molecules to metal atoms determines the size of the cages.

The team’s goal for the new material was to enable it to reversibly switch between two cage sizes: one with 24 atoms of palladium for 48 ligand molecules, and one with 3 palladium atoms for 6 ligand molecules.

Here’s where the photosensitive molecule DTE comes in. The ligand ties to the palladium atom via a nitrogen compound, and as most bonds in chemistry, this forms at a particular angle. The team mixed DTE into the ligand strands to act as a kind of light-operated switch that changes the angle of this bond.

When the material is exposed to ultraviolet (UV) light, this DTE molecule forms a ring and physically pushes the ligand strut away from the palladium — which alters the angle of the bond. This motion breaks apart the cages and forces them to re-form into larger ones.

By contrast, when the material is exposed to green light, that ring is broken, the ligands can tie to the palladium at a sharper angle, and the smaller cages re-form.

In the small-cage state, the material is up to 10 times softer and more dynamic than in the large-cage state, the team reports.

“They can flow when heated up, which means you could cut them and upon mild heating that damage will heal,” Johnson says.

Versatile, but short-lived

The switch takes around five hours to complete, and the team says their material can bear up to seven cycles before breaking down — with each reversal, some of the polymers fail to make the switch, which eventually results in local or wide-spread structural instability.

Still, for such an early stage, these are definitely exciting results. With some more refining, the material could serve in a wide range of applications — similar materials could coat objects such as cars or satellites, giving them a ‘skin’ that can heal damage.

“Anything made from plastic or rubber, if it could be healed when it was damaged, then it wouldn’t have to be thrown away. Maybe this approach would provide materials with longer life cycles,” Johnson adds.

Another potential application could include drug delivery. These could be encapsulated in the cages and released when exposed to UV light — then, upon exposure to green light, the same cages would recapture the substances, giving us a new way to control exactly where and when a drug is released in the body.

However, such applications are still far in the future. Apart from improving the number of cycles these materials can pass through to make them practical, the team also has to work on costs. They used polyethylene glycol (PEG) polymer, which isn’t very pricey and which should be replaceable by any kind of polymer. The real issue is the palladium, which is very rare and very expensive.

Another goal the team has set for the future is to create materials that can switch between a liquid and solid state using a similar system, and to use light to create softer and more solid sections within the same material.

The paper “Photoswitching topology in polymer networks with metal–organic cages as crosslinks” has been published in the journal Nature.

Bendy circuit.

Stretchy, bendy electronic circuits paves way to new wearable tech, bioimplants

Elastic circuits that can bend and stretch are here — and they mean business.

Bendy circuit.

LED circuits interconnected by MPC can undergo repeated bending, twisting, and stretching.
Image credits Tang et al., 2018, iScience.

Chinese researchers have developed a novel hybrid material — part elastic polymer, part liquid metal — that can bend, stretch, and still work as an electric circuit. The material can be cast in most two-dimensional shapes and, based on the polymer used, can be completely non-toxic.

Circuits, with a twist

“These are the first flexible electronics that are at once highly conductive and stretchable, fully biocompatible, and able to be fabricated conveniently across size scales with micro-feature precision,” says senior author Xingyu Jiang.

“We believe that they will have broad applications for both wearable electronics and implantable devices.”

The material the team developed is known as a metal-polymer conductor (MPC). As the name suggests, it’s a combination of two components. The metal bit of the mix carries electric charges — handling the ‘circuit’ part. However, the team didn’t use materials commonly seen in circuits, such as copper, silver, or gold, but settled on gallium and indium. These two metals form a thick fluid that’s a good electric conductor — meaning the circuits can ‘flow’ and still function while accommodating any stretching. The second component is a silicone-based polymer. This imparts mechanical resilience to the circuit, keeping the fluid ‘wires’ all neat and orderly.

Jiang’s team found that embedding globs of this gallium-indium mixture into the polymer substrate created a mechanically-strong material that can function as a circuit. Close-up, the MPC looks like a collection of metal islands in a sea of polymer. A liquid metal mantle runs underneath these islands to ensure conductivity is maintained at all times.

The team successfully trialed different MPC formulations in a wide range of applications — from sensors in wearable keyboard gloves to electrodes embedded in cells. There’s a huge range of applications these MPCs can be used for, they note, limited only by their particular polymer substrate.

“We cast super-elastic polymers to make MPCs for stretchable circuits. We use biocompatible and biodegradable polymers when we want MPCs for implantable devices,” says first author Lixue Tang.

“In the future, we could even build soft robots by combining electroactive polymers.”

The team is also confident that the MPC manufacturing method they developed — it involves screen printing and microfluidic patterning — can be used to produce any two-dimensional geometry. It can also handle different thicknesses and electric properties — which are a function of metal concentration in the circuits. This versatility could allow researchers to rapidly develop flexible circuits for a wide range of uses, the team notes, from wearable tech to bioimplants.

“We wanted to develop biocompatible materials that could be used to build wearable or implantable devices for diagnosing and treating disease without compromising quality of life, and we believe that this is a first step toward changing the way that cardiovascular diseases and other afflictions are managed,” says Jiang.

The paper “Printable Metal-Polymer Conductors for Highly Stretchable Bio-Devices” has been published in the journal iScience.

Renewable flip flops: scientists produce the “No. 1” footwear in the world from algae

Students and researchers at the University of California (UC) San Diego want to fix our plastic problem, one flip flop at a time. They’ve developed and produced the first algae-based, renewable flip flops in the world.

Triton flip flops.

Image credits UC San Diego.

Their first prototypes, developed over the summer months in a York Hall chemistry lab, are pretty basic as far as flip flops go. They’re made of a flexible, spongy sole, a simple strap, and a trident logo. But between its projected cost of $3 per pair and carbon-neutral production process, they might just help change the world’s environments for the better.

Step-by-step

Flip flops are the shoe on Earth. An estimated 3 billion of them find their way into waterways and the ocean each year, constituting a major plastic pollution source for marine environments. That’s because 3 billion petroleum-based flip flops are produced worldwide each year, eventually ending up as non-biodegradable trash in landfills, rivers, and oceans around the globe.

“These are the shoes of a fisherman and a farmer,” says Stephen Mayfield, UC San Diego professor of biology, who headed the research work alongside professor of chemistry and biochemistry Skip Pomeroy. “This is the No. 1 shoe in India, the No. 1 shoe in China and the No. 1 shoe in Africa. And, in fact, one of the largest pollutants in the ocean is polyurethane from flip flops and other shoes that have been washed or thrown into rivers and flow into the ocean.”

Two years ago, the two professors and their graduate and undergrad students developed the world’s first algae-sourced surfboard. Along with a local surfboard blank manufacturer, Arctic Foam of Oceanside, they developed a method to make algae oil hard enough to replace the polyurethane foam core in a surfboard, typically produced from petroleum. It was a big success among the surfing community, which was looking for more sustainable and eco-friendly way to construct boards.

Starting from that research, the duo wanted to expand. Surfboards were “the first obvious product to make” from algae, Mayfield says, but adds that “when you really look at the numbers you realize that making a flip flop or shoe sole like this is much more important.” Seeing the success algae-based foams enjoyed with the 500,000 or so boards sold around the world yearly, they decided to try the same approach for the billions of pairs of flip flops and other footwear that reach landfills (or worse, oceans) each year.

“Depending on how you do the chemistry, you can make hard foams or soft foams from algae oil,” Mayfield explains. “You can make algae-based, renewable surfboards, flip flops, polyurethane athletic shoes, car seats or even tires for your car.”

Mayfield and Pomeroy applied their idea, dubbed Triton Soles, for a $50,000 proof-of-concept grant. They received the funding via the Accelerating Innovations to Market program, initiated by UC San Diego’s Office of Innovation and Commercialization and paid for with the help of local elected officials through State Assembly Bill 2664. The goal of the bill is to bring more laboratory inventions from the campus to commercial development.

From research to retail

Along with Michael Burkart, a professor of chemistry and biochemistry at UC San Diego, Mayfield and Pomeroy formed a startup company called Algenesis Materials. It employs some of the students working on the flip flops, offering them much-needed practical experience in a scientific project with real-world impact.

“Part of the challenge is that typically I’d make a discovery, publish a paper and that’s sort of the end of it,” Mayfield explains. “But the best invention that you keep inside the lab really isn’t valuable for the world. And the way you make that invention valuable is to turn it into a product.”

“Teaching chemistry in the classroom is sometimes like trying to teach soccer at the chalkboard,” Pomeroy adds. “In the laboratory, students are far more engaged when they’re actually trying to solve a problem. Most people will tell you that our students are really, really bright, but they don’t always have practical experience.”

“This is a way to provide them with that.”

As Algenesis Meterials’ first product, the Triton will represent the platform on which the faculty members and students will work to refine the chemistry and manufacturing process. In time, they hope the experience will allow them to replace more petroleum-based products, such as shoe soles, car seats, or tires. The lion’s share of our oil today is, after all, originated from algae — and it is Mayfield’s hope that “anything we can make from petroleum we can ultimately make from algae.”

Triton manufacturing.

Image credits UC San Diego.

The Tritons — and any other polyurethane items made from algae oil — are more eco-friendly than their petroleum-based counterparts because the carbon used to manufacture them is captured from the atmosphere, not sourced from oil reserves. The team is also looking to make them biodegradable by converting the algae oil into polyurethane while allowing the carbon bonds inside the plastic to be degraded by microorganisms. The end goal is to make flip flops that “can be thrown into a compost pile and they will be eaten by microorganisms,” Mayfield says.

“If we can make these products sustainable and biodegradable, we can impact not only San Diego, but every beach community on the entire planet,” he says. “In San Diego, we have this fantastic surfing culture, many of our faculty and students are surfers, and I think all of us understand because of that connection to the ocean how important the environment is.”

They plan to have the flip flops commercially available sometime in 2018.

Green Rubber.

Your phone’s case and your car’s tires may soon be made from renewable, plant sugars

Researchers from a trio of U.S. universities have developed a technique to produce butadiene — a molecule traditionally sourced from oil or natural gas that underpins synthetic rubber and plastics — from renewable sources.

Green Rubber.

Rubber is going green.
Image credits Hans Braxmeier.

Butadiene is the prime building block used for a whole bunch of materials we use today. It can be strewn together/polymerized to create styrene-butadiene rubber, the stuff quality tires are made of (apart, of course, from those made from eggshells and tomatoes). As nitrile butadiene rubber, it’s used to make hoses, seals, and the ubiquitous medical rubber glove. Butadiene is also the main component in acrylonitrile-butadiene-styrene, a rigid plastic that can be molded into hardy shapes — your computer or console case is likely made from this substance.

But getting your hands on butadiene does pose one economic and ecological problem — you need to refine natural hydrocarbons such as oil and gas to produce it. So understandably, there has been a push develop renewable (and if at all possible, cheaper) methods of obtaining this monomer. One new paper describes exactly one such method: the team — from the University of Delaware, the University of Minnesota and the University of Massachusetts — has invented a process to make butadiene from renewable sugars found in trees, grasses, and corn.

“Our team’s success came from our philosophy that connects research in novel catalytic materials with a new approach to the chemistry,” says University of Delaware-based Catalysis Center for Energy Innovation Director Dionisios Vlachos, the Allan and Myra Ferguson Professor of Chemical and Biomolecular Engineering at UD and a co-author of the study. “This is a great example where the research team was greater than the sum of its parts.”

“Our team combined a catalyst we recently discovered with new and exciting chemistry to find the first high-yield, low-cost method of manufacturing butadiene,” he adds. “This research could transform the multi-billion-dollar plastics and rubber industries.”

The three-step process begins with biomass-derived sugars. Using technology developed at the CCEI, the team can convert this sugars into a ring-like compound named farfural. This substance is then further processed into another ring compound called tetrahydrofuran (THF). The innovative third step uses phosphorus all-silica zeolite, a catalyst also developed at the CCEI, to break the THF rings into butadiene with more than 95 percent efficiency — considered a high-yield process in chemical manufacturing.

The reaction’s “before and after.”
Image credits P. J. Dauenhauer et al., (2017), ACS.

The authors coined this novel, selective reaction “dehydra-decyclization” to show its capability for simultaneously removing water and cracking THF at once.

The paper “Biomass-Derived Butadiene by Dehydra-Decyclization of Tetrahydrofuran” has been published in the journal ACS Sustainable Chemistry & Engineering.

By adding fibers, scientists have turned a soft gel into a material tougher than many metals. Credit: Hokkaido Uni.

Adding fibers to hydrogel, a soft material mostly made of water, makes it 5 times tougher than steel

By adding fibers, scientists have turned a soft gel into a material tougher than many metals. Credit: Hokkaido Uni.

By adding fibers, scientists have turned a soft gel into a material tougher than many metals. Credit: Hokkaido Uni.

Hydrogels are made of a network of polymer chains that are hydrophilic. For this reason, this material can absorb up to 90% of its weight in water making the hydrogel highly flexible, mimicking natural tissue. On the flipside, hydrogels aren’t very strong. However, Japanese researchers from Hokkaido University have found a way to make very strong hydrogels by introducing fibers into their composition without compromising too much flexibility. The fiber-reinforced hydrogels are five times tougher than steels according to tests ran in the lab.

Due to its properties, hydrogel is used for medical purposes in tissue engineering as well as sustained-release of drug delivery system or rectal diagnoses. It also has the potential to become a very useful structural material if only it could be coaxed to be stronger for long-term use.

The Japanese team led by Dr. Jian Ping Gong looked at the problem and decided to go with a time-honored approach: just mix and match with some other material to create a composite material that has all of the desired properties. For instance, mud is mushy but add some straw to it and leave it to bask in the sun for a while and you have some pretty functional solid bricks. It’s how people used to make their homes for thousands of years.

Likewise, the researchers added glass fiber fabric to polyampholyte (PA) hydrogels that contained high levels of water. Though the fibers were no bigger than 10μm in diameter, slightly thinner than the human hair, the resulting composite material proved to be bendable and very strong at the same time.

Scanning Electron Microscopy (SEM) images of the fiber-reinforced hydrogels. The polymer matrix (arrows) filled the interstitial space in the fiber bundles and connected the neighboring fibers. (Huang Y. et al., Advanced Functional Materials, January 16, 2017)

Scanning Electron Microscopy (SEM) images of the fiber-reinforced hydrogels. The polymer matrix (arrows) filled the interstitial space in the fiber bundles and connected the neighboring fibers. (Huang Y. et al., Advanced Functional Materials, January 16, 2017)

Lab tests show the fiver-reinforced hydrogels are 25 times tougher than glass fiber fabric and 100 times tougher than unaltered hydrogels. That makes it 5 times tougher than carbon steel. The researchers measured the energy required to destroy them when assessing the materials’ strength.

It’s not certain yet but the Japanese researchers think this high toughness is due to an increase in dynamic ionic bonds between the fiber and hydrogels, as well as within the gels themselves.

The manufacturing process is quite simple — you only have to immerse the fabric in PA precursor solutions for polymerization — and should prove scalable.

“The fiber-reinforced hydrogels, with a 40 percent water level, are environmentally friendly,” Gong said in a statement. “The material has multiple potential applications because of its reliability, durability and flexibility. For example, in addition to fashion and manufacturing uses, it could be used as artificial ligaments and tendons, which are subject to strong load-bearing tensions.”

The same process, reported in the journal Advanced Functional Materials should be able to make other polymers tougher, like rubber.

Additive recycles incompatible mixed plastics into uber-polymer

A new four-block polymer could finally allow for chemically-incompatible plastics to be recycled together. The best part? The resulting material has better physical properties than either of the materials taken individually.

Image credits Hans Braxmeier.

Cornell University Professor of chemistry Geoffrey Coates is a big believer in plastic recycling. He often gives talks on the subject, and routinely starts these off with a simple question: How much of the 78 million tons of plastic used for packaging each year gets recycled and re-used by the industry?

A world wrapped in plastic

The answer is ‘depressingly little’ — just over 2%. A third of the total quantity gets leaked into the environment, he adds, some 14% goes to incinerators or other energy recovery methods, and the lion’s share — 40% — finds its way into landfills. Where it will stay virtually forever.

One of the biggest problems, he goes on to explain, is that the two most common types of plastics — polyethylene (PE) and polypropylene (PP), which account for two-thirds of all plastics — are chemically incompatible and can’t be processed together.

But work performed in Coates’ lab may finally change that. He and his team have collaborated with researchers from the University of Minnesota to develop a new polymer that can reconcile PE and PP. A small quantity of this substance can bind the two plastics into a new, mechanically tougher polymer.

Their additive is a four-block polymer, constructed of alternating PE and PP segments. It resembles a chemical zipper of sorts, each segment tying to one of the two polymers. To test how strong the resulting material is, the team compared it to available diblock (two-block) polymers. For the tests, they welded together two strips of plastic with different polymer adhesives then pulled them apart to see how much strain the weld can take.

Welds made with diblock polymers failed relatively quickly, but the new tetrablock polymer held so well that the plastic strips before it gave way.

 

 

“People have done things like this before,” Coates said, “but they’ll typically put 10 percent of a soft material, so you don’t get the nice plastic properties, you get something that’s not quite as good as the original material.”

“What’s exciting about this is we can go to as low as 1 percent of our additive, and you get a plastic alloy that really has super-great properties.”

Better living through chemistry

Image credits Michael Schwarzenberger.

While the tetrablock polymer was intended to allow wide-scale plastic recycling, it may go above and beyond the call of duty says James Eagan, a postdoc researcher in Coates’ team and lead author of the paper. The additive could usher in a whole new class of tougher polymer blends, allowing for wider applications and improving sustainability in one shot.

“If you could make a milk jug with 30 percent less material because it’s mechanically better, think of the sustainability of that,” he said. “You’re using less plastic, less oil, you have less stuff to recycle, you have a lighter product that uses less fossil fuel to move it.”

Although ideal, a world where all the plastics we use is recycled sadly remains an unreachable goal. But between this new polymer and previous work on bio-degradable plastics, we definitely have the tools to start undoing — or at least capping — the damage polymers have wrought on the planet. Both technologies are still far from perfect, but they’re workable. There are also policy measures which have shown effectiveness in limiting this pollution in the first place — such as taxes, alternative material use, and outright bans. Let’s hope they’re all put to good use removing plastic waste sooner rather than later.

The full paper “Combining polyethylene and polypropylene: Enhanced performance with PE/ i PP multiblock polymers” has been published in the journal Science.

Chocolate-inspired technique helps researchers develop better polymer shells

For centuries, chocolatiers have been trying to develop the perfect chocolate coating for bonbons, honing their skill to the point of artistic performance. But scientists believe they can take things even further. A group of MIT researchers believe they’ve come up with the perfect chocolate coating technique, a technique that could have many applications outside the food industry.

Tartufo, a desert covered in chocolate. Photo by Anna Fox

Bonbons can come in a large variety of shapes, sizes and tastes – but the most loved ones are without a doubt small candies coated in chocolate. The first reports about bonbons come from the 17th century, when they were made at the French royal court.

“Think of this formula as a recipe,” says Pedro Reis, the Gilbert W. Winslow Associate Professor of mechanical engineering and civil and environmental engineering at MIT. “I’m sure chocolatiers have come up with techniques that give empirically a set of instructions that they know will work. But our theory provides a a much better, quantitative understanding of what’s going on, and one can now be predictive.”

Reis and his team were inspired by videos of chocolatiers making bonbons and other chocolate shells. They pour the chocolate into molds, allowing excess chocolate to flow out, creating a shell of uniform thickness. But Reis was curious: was there a way to accurately predict the thickness of the resulting shell? He set out to explore this seemingly frivolous question, alongside lead author and graduate student Anna Lee, postdoc Joel Marthelot, and applied mathematics instructor Pierre-Thomas Brun, along with colleagues from the team of François Gallaire at the Swiss Federal Institute of Technology in Lausanne, Switzerland.

Initially, Lee and Marthelot used an analogous technique to experimentally create their own shells, using not chocolate but a polymer solution that they drizzled over dome-shaped molds and spheres.

They found that again and again, the coating had equal thickness on all sides (they cut the balls in half to test this). So they set out and determined the mathematical formula for the thickness of the shell, which is basically the square root of the fluid’s viscosity, times the mold’s radius, divided by the curing time of the polymer, times the polymer’s density and the acceleration of gravity as the polymer flows down the mold.

It sounds like a complicated formula, but it boils down to this: the bigger the mold, the thicker the shell, because it takes the fluid longer to flow to the bottom. The longer the curing time, the thinner the shell will be. Armed with that knowledge, they could go crazy with polymer models and see how to obtain shells of the desired thickness.

“You could go in the lab and lay down tons of ping pong balls and test various initial conditions, which is what Anna and Joel have been doing to some extent, but with numerics, you can get really creative,” Brun says.

Ultimately, they found that by tampering with the curing time, they can create much thicker coatings, which can be significant not only for the materials industry, but also for medical purposes

“By waiting between mixing and pouring the polymer, we can increase the thickness of a shell by a factor of 11,” says Lee.
“This flexibility of waiting gives us a simple parameter we can tune, depending on what we want for our final goal,” Reis says. “So I think ‘rapid fabrication’ is how we can describe this technique. Usually that term means 3-D printing and other expensive tools, but it could describe something as simple as pouring chocolate over a mold.”

A multiple-exposure image of a new shape-memory polymer reverting to its original shape after being exposed to body temperature. (University of Rochester photo / J. Adam Fenster)

Novel polymer changes shape just by touching with a finger — lifts 1,000 times its own weight doing so

This polymer can change shape and release tremendous amounts of stored elastic energy relative to its weight simply by being exposed to a temperature change. This in itself isn’t exactly new, but the team led by Chemical Engineering Professor Mitch Anthamatten at the University of Rochester innovated by making the polymer react to room temperature — a first.

A multiple-exposure image of a new shape-memory polymer reverting to its original shape after being exposed to body temperature. (University of Rochester photo / J. Adam Fenster)

A multiple-exposure image of a new shape-memory polymer reverting to its original shape after being exposed to body temperature. (University of Rochester photo / J. Adam Fenster)

The material belongs to a class called shape-memory polymers. These materials can be programmed to retain a specific shape until triggered to return to the original shape — in our case, by heat.

“Our shape-memory polymer is like a rubber band that can lock itself into a new shape when stretched. But a simple touch causes it to recoil back to its original shape,” said Anthamatten in a statement.

 

To reach this level of control, the polymer’s crystallization that occurs when it gets cooled or stretched was tweaked just right. When deformed, chains of the memory polymer become stretched while smaller segments become aligned in the same direction across small areas. This fixes the material. The more of these concentrated areas you have in the material, the more stable the shape and the more difficult it is for the material to revert back to its original shape.

Eventually, the researchers learned to trigger the material rewind to any temperature by including molecular linkers to connect the individual polymer strands. In one demonstration, the polymer was set to revert back to its original shape at sub room temperature. Touching the material with one finger was enough.

What’s amazing is that once triggered, the polymer releases its stored elastic energy. Anthamatten’s shape-memory polymer is capable of lifting an object one-thousand times its weight. For example, a polymer the size of a shoelace—which weighs about a gram—could lift a liter of soda. As a demonstration, his team used a small band of the material to pull a toy truck up an incline or lifting weights.

This is cool, but any practical use for it? Anthamatten says his shape-memory polymer could prove very handy as sutures, artificial skin, body-heat assisted medical dispensers, and self-fitting apparel.

MIT polymer paves the way for solar-heated clothes

MIT scientists have developed a material that can absorb solar energy, store and release it on demand to produce heat. Made from a film of polymer, the material could be used to used to tailor cold climate garments that charge up during the day and keep you pleasantly warm in the evening.

Image via inhabitat

The polymer weave absorbs energy from the sun’s rays and stores it through chemical reactions within a transparent film. The material contains certain molecules that move into a “charged position” when exposed to sunlight.

Storing energy in a chemical form is desirable as the compounds are stable enough to allow the user to draw on the reserves at their own discretion. The energy from the material can be released with widely available catalysts. For example, the heat stored in a solar-charged jacket can be released when it’s subjected to a powerful flash of light or when exposed to an electrical current.

The team claims the polymer can heat up to 60 degrees Fahrenheit, and it can store solar energy for an indefinite amount of time.

If applied to clothing, the sun-storing material could benefit everyone from athletes or cold-weather workers, as well as regular fashionistas living in chilly environments.

Researchers say the film is easy to produce, in a two step process. They are looking to apply the energy-harvesting film to materials and products like clothing, window glass and industrial products.

self-healing plastic

Self-healing bioplastic stitches itself back together when water is added

When your plastic device breaks, there’s basically nothing else to do but shrug, try to glue it then go on with your life. But wouldn’t it be  useful if the plastic itself could fix itself? Let me illustrate with the latest creation to come off the  Pennsylvania State University lab: a bioplastic containing a novel mix of proteins derived from squid sucker ring teeth that can fuse back together when water is added. Once its ‘healed’, the bulk bioplastic return to its previous compression and tensile strength, so its not fragile.

self-healing plastic

Image: Penn State

Prof. Melik Demirel had been curious about the self-healing abilities of squid sucker teeth for some time. Upon investigation, he found that although the exact composition of the teeth varied species to species, there were some key proteins common to all squids which were responsible for this ability.

Extracting the proteins from squids proved counter-productive since the yield was very low. It also meant a lot of animals had to be processed. So, a solution was to harvest these proteins from genetically modified bacteria, a sort of biological factories. The proteins weren’t alone, however, but joined as a copolymer. Basically, an additional portion made up of  strands of amino acids connected by hydrogen bonds was added to the polymer.

When the researchers cut a sample of the polymer in half then added a bit of water and applied pressure, the material fused back together. Stress tests showed that the bulk material was just as strong or bendable as prior to the suture.

“If one of the fiber-optic cables under the ocean breaks, the only way to fix it is to replace it,” said Demirel. “With this material, it would be possible to heal the cable and go on with operation, saving time and money.

“Maybe someday we could apply this approach to healing of wounds or other applications,” he said. “It would be interesting in the long run to see if we could promote wound healing this way so that is where I’m going to focus now.”

New Silicone Technology Creates Super Slippery, Anti-Bacterial Surface

A new liquid-infused polymer can make sure that medical equipment is bacteria free by being extremely slippery. This technology, which involves silicone infused with a silicone oil also has a myriad of potential applications outside of medical equipment – in the oil industry, in air planes and cosmetics.

Harvard researchers have demonstrated a powerful, long-lasting repellent surface technology that can be used with medical materials to prevent infections caused by biofilms. (Image courtesy of Joanna Aizenberg, via Harvard University)

According to the National Institutes of Health, over 80 percent of all infections in the human body are caused by a build-up of bacteria. Bacteria accumulates into adhesive colonies called biofilms, which help them survive and protect them from outside threats. Common soaps don’t actually destroy the bacteria, but they make a slippery surface on your skin making it so that bacteria can’t attach themselves to you and fall off – this is the main idea here too.

Such bacterial biofilms tend to form on medical equipment, including surgery equipment heart valves, urinary catheters, intravenous catheters, and implants. Naturally, we don’t want that to happen – as it can be extremely dangerous. Now, a new study demonstrated a long-lasting repellent surface technology that can be used with medical materials to prevent infections caused by biofilms.

The new technology (liquid-infused polymers) can store considerable amounts of lubricant in their molecular structure, much like a sponge holds liquids. This lubricant can then travel to the surface, repelling the bacterian and blocking the environment in which it forms. The team led by Joanna Aizenberg from Harvard is now working on designing several such liquid-infused polymer systems which could be applied on various medical surfaces. However, super-slippery surfaces can have applications in more fields, including keeping glass clean, making better cosmetics and ensuring that ice doesn’t stick to airplane wings.

For this study, they used both a silicone material, and a silicone oil, which are non toxic and safe to use.

“The solid silicone tubing is saturated with silicone oil, soaking it up into all of the tiny spaces in its molecular structure so that the two materials really become completely integrated into one,” said Caitlin Howell, a Postdoctoral Researcher at the Wyss Institute and a co-author on the new findings.

To test the effectiveness of the super slippery surface, the study’s lead author Noah MacCallum, an exchange undergraduate student at SEAS, exposed treated and untreated medical tubing to Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus epidermidis, which are common pathogenic bacteria that form biofilms and are the most common culprits in blood and urinary infections. The experiment confirmed what scientists believed – that the surface greatly reduces biofilm adhesion and largely (though not totally) eliminated biofilm formation. The results give great hope for future applications and reducing infections, especially with drug-resistant bacteria.

“With widespread antibiotic resistance cropping up in many strains of infection-causing bacteria, developing out-of-the-box strategies to protect patients from bacterial biofilms has become a critical focus area for clinical researchers,” said Wyss Institute Founding Director Donald Ingber, who is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Boston Children’s Hospital and Professor of Bioengineering at Harvard SEAS. “Liquid-infused polymers could be used to prevent biofilms from ever taking hold, potentially reducing rates of infection and therefore reducing dependence on antibiotic use.”

As for applying super-slippery surfaces to other fields, the authors have big plans.

. “We could apply liquid-infused polymers to other materials plagued with biofouling problems, such as waste-water management systems, maritime vessels or oil pipes,” said one of the study’s lead co-authors Philseok Kim, who was formerly a Senior Research Scientist at the Wyss Institute and is currently co-founder and Vice President of SLIPS Technologies, Inc.

However, before we can speak of actually implementing super slippery surfaces into waste water management or the oil industry, the technology has to prove its efficiency in experimental results. Still, the development shows great promise, and I’m certain we’ll be hearing more from it in the near future.

“Each technology in our portfolio has different properties and potential uses, but collectively this range of approaches to surface coatings can prevent a broad range of life-threatening problems, from ice accumulation on airplane wings to bacterial infections in the human body,” said Aizenberg.

 

Journal Reference: Noah MacCallum et al. Liquid-Infused Silicone As a Biofouling-Free Medical Material. DOI: 10.1021/ab5000578

Schematic representation of a polymer gel whose chains are cross-linked using rotating molecular motors (the red and blue parts of the motor can turn relative to each other when provided with energy). Right: When exposed to light, the motors start to rotate, twisting the polymer chains and contracting the gel by as much as 80% of its initial volume: in this way, part of the light energy is stored as mechanical energy. © Gad Fuks / Nicolas Giuseppone / Mathieu Lejeune

Gel contracts like muscle and stores light energy

Researchers at the Université de Strasbourg  made a polymer gel that is able to contract similar to how a muscle concentrates motor proteins to elicit motion. The contraction occurs under the influence of light, but besides contraction, the gel also stores some of the absorbed light.

A gel battery

Schematic representation of a polymer gel whose chains are cross-linked using rotating molecular motors (the red and blue parts of the motor can turn relative to each other when provided with energy). Right: When exposed to light, the motors start to rotate, twisting the polymer chains and contracting the gel by as much as 80% of its initial volume: in this way, part of the light energy is stored as mechanical energy. © Gad Fuks / Nicolas Giuseppone / Mathieu Lejeune

Schematic representation of a polymer gel whose chains are cross-linked using rotating molecular motors (the red and blue parts of the motor can turn relative to each other when provided with energy). Right: When exposed to light, the motors start to rotate, twisting the polymer chains and contracting the gel by as much as 80% of its initial volume: in this way, part of the light energy is stored as mechanical energy. © Gad Fuks / Nicolas Giuseppone / Mathieu Lejeune

Muscles, like most living systems, perform functions at the macroscale through the collective molecular motion at the nanoscale. These molecular motors are highly complex protein assemblies that can produce work by consuming energy. For example, many protein-based molecular motors harness the chemical free energy released by the hydrolysis of ATP in order to perform mechanical work. Basically, these underlie all motion processes in biological systems (like the human body), but also work to copy DNA and synthesize proteins.

Individually, these molecular motors operate over an extremely short distance in the nano range. Yet, when millions join up they behave in a coordinate matter and collectively produce effects at the macroscale.

For a long while, scientists have been trying to mimic this behavior and produce artificial molecular motors. Undeterred by previous failed attempts, researchers at the Institut Charles Sadron, led by Nicolas Giuseppone, professor at the Université de Strasbourg, replaced a gel’s reticulation points, which cross-link the polymer chains to each other, by rotating molecular motors made up of two parts that can turn relative to each other when provided with energy. When light was shone, the artificial motors activated twisting the polymer chains in the gel, causing it to contract.

Just as in living systems, the motors consume energy in order to produce continuous motion. However, this light energy is not totally dissipated: it is turned into mechanical energy through the twisting of the polymer chains, and stored in the gel. But it’s not very much for now. According to the paper published in Nature Nanotechnology, the gel only converts 0.15% of the incoming energy into mechanical energy via contractions.

The plan is to exploit the gel somehow by finding a feasible way to extract the stored energy. Something like solar powered gel batteries, but it’s still very early to tell how this research will fair in the future.

Expanding Brain Samples to Better See Them

Researchers from the Massachusetts Institute of Technology (MIT) have found a way to enlarge and map brain samples. This inexpensive technique will now allow scientists to get a much closer look at the human brian and perhaps figure out some of its long standing secrets.

Using a new technique that allows them to enlarge brain tissue, MIT scientists created these images of neurons in the hippocampus.
Image: Fei Chen and Paul Tillberg

Ever since the 1500s when microscopes were first developed, people have wanted to zoom in more and more. But scientists working at MIT decided to take a different approach, and instead of zooming in with the microscope, they simply made the samples bigger. Of course, that’s nowhere near as easy as it sounds. They did this by embedding samples in a polymer that swells when water is added. This allows specimens to be physically magnified, and therefore imaged at a much higher resolution.

What makes this technique even more interesting is the fact that it uses relatively cheap materials. The chemicals and materials required are commonly available everywhere.

“Instead of acquiring a new microscope to take images with nanoscale resolution, you can take the images on a regular microscope. You physically make the sample bigger, rather than trying to magnify the rays of light that are emitted by the sample,” says Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT.


The thing is, with conventional microscopes, there is a physical limit to how much you can magnify. Microscopes use lenses to focus light emitted from a sample into a magnified image. However, when you get to things which are comparable in size to the wavelength of light, things start to get tricky – and you actually can’t magnify things smaller than that wavelength. When scientists do want to image at this level, they use electron microscopes. This is a big problem.

“Unfortunately, in biology that’s right where things get interesting,” says Boyden, who is a member of MIT’s Media Lab and McGovern Institute for Brain Research. Protein complexes, molecules that transport payloads in and out of cells, and other cellular activities are all organized at the nanoscale.

Scientists have tried several approaches to get past this limit, but this is the first time the sample was focused, instead of the microscopy technique. The idea is to embed samples in an expandable polymer gel made of polyacrylate, a very absorbent material found in many common products, such as diapers.

“Once the tissue is labeled, the researchers add the precursor to the polyacrylate gel and heat it to form the gel. They then digest the proteins that hold the specimen together, allowing it to expand uniformly. The specimen is then washed in salt-free water to induce a 100-fold expansion in volume. Even though the proteins have been broken apart, the original location of each fluorescent label stays the same relative to the overall structure of the tissue because it is anchored to the polyacrylate gel”, MIT’s press room writes.

In a different study, MIT neuroscientists used calcium imaging to label these pyramidal cells in the brain. Image: Qian Chen

Using this technique, researchers managed to image a section of brain tissue 500 by 200 by 100 microns with a standard confocal microscope. Imaging such large samples would not be feasible with other super-resolution techniques, which require minutes to image a tissue slice only 1 micron thick. The resolution wasn’t diminished in any way either, which makes it even more spectacular.

“The exciting part is that this approach can acquire data at the same high speed per pixel as conventional microscopy, contrary to most other methods that beat the diffraction limit for microscopy, which can be 1,000 times slower per pixel,” says George Church, a professor of genetics at Harvard Medical School who was not part of the research team.

According to their study, this is the only way to truly analyze such samples.

“The other methods currently have better resolution, but are harder to use, or slower,” Tillberg says. “The benefits of our method are the ease of use and, more importantly, compatibility with large volumes, which is challenging with existing technologies.”

Source: MIT.

 

Touch invisibility cloak prevents objects from being felt

With the finger or a force measurement instrument, no information is obtained about the bottom side of the material. Credit: T Bückmann / KIT

In the past years, several types of invisibility cloaks have been developed, hiding objects not only from light, but also from sound and even heat. But this is the first time an invisibility cloak for touch has been developed.

Recently, we’ve written quite a lot about invisibility cloaks – how they work, how they can be improved, and what real life applications they have (aside from being really cool) – like for example protecting cities from earthquakes (yeah, really). But what about a  “touch invisibility cloak” ? Naturally, it is constructed very differently – based on a metamaterial that consists of a polymer with a special structure.

“We build the structure around the object to be hidden. In this structure, strength depends on the location in a defined way,” explains Tiemo Bückmann, KIT, the first author of the article. “The precision of the components combined with the size of the complete arrangement was one of the big obstacles to the development of the mechanical invisibility cloak.”

The metamaterial in case is actually in a crystalline material, built with extreme sub-micrometer accuracy; it basically consists of needle-shaped cones, whose tips meet. The size of the contact points is calculated precisely to reach the mechanical properties desired. The resulting structure is built in such a way that a finger or a measuring instrument cannot feel its way through it.

“It is like in Hans-Christian Andersen’s fairy tale about the princess and the pea. The princess feels the pea in spite of the mattresses. When using our new material, however, one mattress would be sufficient for the princess to sleep well,” Bückmann explains.

So far, this is pure research – no end goal in sight. However, since it paves the way for producing materials with freely selectable mechanical properties, it could have a myriad of applications. The first that pop to mind are comfier mattresses or rugs under which you can sneak a cable or two and not feel them; however, investing in such a high-end technology for this type of results is not something doable at the moment.

Journal Reference:
T. Bückmann, M. Thiel, M. Kadic, R. Schittny, M. Wegener. An elasto-mechanical unfeelability cloak made of pentamode metamaterials. Nature Communications, 2014; 5 DOI: 10.1038/ncomms5130

flexible_semiconducting_polymer

A first step towards making ‘plastic’ semiconductors for stretchy-electronics

Stanford chemical engineers have developed a theoretical model that sheds light on the electrical conductivity properties of polymers. Their work provides a valuable first step for other researchers to build on, providing an experimental setting for those looking to expand the electrical conductivity of certain polymers (typically plastics) for use in the industry.

The word “polymer” is derived from the Greek for “many parts” which aptly describes their simple molecular structure, which consists of identical units, called monomers, that string together, end to end, like so many sausages. Humans have long used natural polymers such as silk and wool, while newer industrial processes have adapted this same technique to turn end-to-end chains of hydrocarbon molecules, ultimately derived from petroleum byproducts, into plastics.

The constitutive elements that go in your typical electronics like your smartphone or notebook include things like circuitry, transistors, condensers and so on, all typically made out of metallic materials, since these need to be electrically conductive. At the same time, however, these materials, like the reigning king silicon, are brittle and fairly stiff.

Fad or not, in recent years scientists have made various attempts at developing electronics capable of being stretched a significant or even multiple times their width, as well rolling. Imagine clothing electronics, tablets that can fold like a newspaper, a whole range of new possibilities. As such, many have experimented with polymers which are more flexible. It’s clear that there’s a serious trade-off problem here that engineers need to tackle: metals can’t stretch but they conduct electricity better, polymers can stretch, but conduct electricity poorly. Things don’t need to be all black and white, though. The best and quickest solutions are found when engineers have access to as much data and information about the problem they’re trying to solve as possible.

Stanford chemical engineering professor Andrew Spakowitz and colleagues  the first theoretical framework that includes the molecular-level structural inhomogeneity of polymers. Metals have a regular molecular structure that allows electrical current to flow smoothly, but this is also what makes them rigid. Polymers on the other hand, at a molecular level, look more like a bowl of spaghetti: strands are coiled  or run relatively true, even if curved, like lanes on a highway. This variability of molecular structure is reflected in the variability of electrical conductivity as well. In the process of experimenting with polymeric semiconductors, researchers discovered that these flexible materials exhibited “anomalous transport behavior” or, simply put, variability in the speed at which electrons flowed through the system.

“Prior theories of electrical flow in polymeric semiconductors are largely extrapolated from our understanding of metals and inorganic semiconductors like silicon,” Spakowitz said, adding that he and his collaborators began by taking a molecular-level view of the electron transport issue.

flexible_semiconducting_polymer

The yellow electric charge races through a ”speed lane” in this stylized view of a polymer semiconductor, but pauses before leaping to the next fast path. Stanford engineers are studying why this occurs with an eye toward building flexible electronics. (Credit: Professor Andrew Spakowitz)

This insight is fundamental to future experiments and research dwelling into building stretchy electronics. One other important hallmark of the Stanford scientists’ paper is that they provide a simple algorithm that begins to suggest how to control the process for making polymers, with an emphasis on how manipulating their electrical conductivity properties.

“There are many, many types of monomers and many variables in the process,” Spakowitz said. The model presented by the Stanford team simplifies this problem greatly by reducing it to a small number of variables describing the structural and electronic properties of semiconducting polymers.

“A simple theory that works is a good start,” said Spakowitz, who envisions much work ahead to bring bending smart phones and folding e-readers to reality.

The author’s theory was published recently in the journal Proceedings of the National Academy of Sciences.

chemical-bond

New anti-fragile plastic becomes stronger every time it’s stressed

Say hello to drop-proof smartphones and whole new generation of plastic products that will be far more durable and strong than their present counterparts. Scientists at Duke University recently unveiled their most recent, stunning work: a new type of polymer that seems to contradict common knowledge and re-arranges its chemical structure each time its under stress, say a mechanical shock. The test of time is in the plastic’s favor as every time the material suffers a mechanical deformation, it becomes stronger.

Plastics are the most widely used class of materials, and there’s no secret why: they’re durable, light, easy to manufacture and they last a long time (they’re lengthy half-life is also an environmental hazard, however) . Their hardness comes in various degrees, however, but what’s certain is that most of us have come to know that plastics aren’t the strongest materials. Bashed house appliances and just about any dropped plastic-based item serve as testament to this claim.

The Duke-made plastic is different. Like most plastics, the polymer is mostly made of carbon. The key difference is that these carbon atoms are arranged in a series of triangles extending down in long chains with two bromine atoms at one point. It’s this unique structure that allows the novel plastic to exhibit its unique, counter-intuitive properties.

chemical-bond

When the plastic is tugged or comes under shock, the polymer chains tear on one side, as opposed to typical plastic polymers who do not experience the same uniform deformation leading to structural failure (breaks, cracks). The shearing force breaks the triangle into a longer chain, which also frees up bonding sites at the bromine locations for a second molecule to come in. That second molecule is a carboxylate that cross-links multiple chains and increases the material’s strength at the site of damage. This happens every time the material comes under deformation.

The material was put to the test on a larger scale after the polymer was introduced into an extruder, which forced the plastic into a mold. Before being placed intro the extruder the material was pliable, but after being molded its hardness increased significantly to the point it become very stiff. Microscopic analysis subsequently showed an increased in hardness 200-fold after the extrusion process.

It’s unclear when the polymer might be introduced in commercial applications, still the prospects are amazing.

Findings appeared in Nature. [via ExtremeTech]

 

Science ABC: Hippos red sweat

Ever since the days of the ancient Greek, people were puzzled by the fact that apparently, hippos sweat blood; this belief propagated for more than a millenium.

hippos

Now, we know that the thick red substance, which oozes from glands all over its skin, is one of the hippo’s many ingenious survival tools. Thing is, hippos are very routine-dependent animals: they spend most of the night eating (literally as much as they can), and when dawn hits, they retire into water and spend their days resting and digesting. Of course, when you want the day off to chill and digest, Sun is a big enemy, so you want some kind of UV protection. But something like fur isn’t the best option when you spend so much time in water, so hippos came up with something else: an anti-UV secretion, which is at first colourless, then red, then finally brown as the pigment polymerizes.

There are two different pigments, both which act as sunscreen, but one of them actually being a very effective antibiotic. At concentrations even lower than that found on the hippo’s skin, it can inhibit the growth of two types of pathogenic bacteria – this is particularly good, because hippos often fight, gaining some nasty open woods which are prone to infection.

The future's fingerprint: organised structures for denser hard drives. Image: University of Texas at Austin

Self-assembling polymer increases HDD memory capacity by a factor of five

Data storage has reached great heights in the past two decades. You can now fit in a typical PC hard-drive thousands of CDs and millions of floppy disks (who else remembers these?). However, magnetic hard drive developers have almost reached the physical limit to where they can cram up data. Researchers at University of Texas at Austin  used a novel technique that makes use of self-assembling polymers to create the smallest magnetic dots in the world. Their results show that hard disk storage can be increased by a factor of five.

The future's fingerprint: organised structures for denser hard drives. Image: University of Texas at Austin

The future’s fingerprint: organised structures for denser hard drives. Image: University of Texas at Austin

Magnetic hard drives store information by inscribing  zeros and ones as magnetic dots on a continuous metal surface. The closer you position these dots from one another, the more information you can cram inside. However, there’s little room developers can move nowadays as the maximum density of dots has almost been reached. Any closer positioning would cause the dots to become unstable from their neighbors’ magnetic field.

“The industry is now at about a terabit of information per square inch,” said Willson, who co-authored the Science paper with chemical engineering professor Christopher Ellison and a team of graduate and undergraduate students. “If we moved the dots much closer together with the current method, they would begin to flip spontaneously now and then, and the archival properties of hard disk drives would be lost. Then you’re in a world of trouble. Can you imagine if one day your bank account info just changed spontaneously?”

There’s a work around, however. If you can isolate each individual dot from another, then you can bypass the magnetic field issue and increase the dot density, and in turn storage. This is where the scientists worked their magic after they used the  directed self-assembly (DSA) – a method pioneered by University of Wisconsin and MIT.

“I am kind of amazed that our students have been able to do what they’ve done,” said Willson. “When we started, for instance, I was hoping that we could get the processing time under 48 hours. We’re now down to about 30 seconds. I’m not even sure how it is possible to do it that fast. It doesn’t seem reasonable, but once in a while you get lucky.

Previous attempts have rendered dot density just enough to double the storage density of disk drives. That’s pretty impressive, but Ellison and co. when way higher. They’ve synthesized block copolymers that self-assemble into the smallest dots in the world — 9 nanometers or just about the size of protein. These were attached to a guided surface which had dots and lines etched on it. While the polymers were self-assembling into position, a special top coat that goes over the block copolymers was introduced. This top coat allows the polymers to achieve the right orientation relative to the plane of the surface simply by heating.

“The patterns of super small dots can now self-assemble in vertical or perpendicular patterns at smaller dimensions than ever before,” said Thomas Albrecht, manager of patterned media technology at HGST. “That makes them easier to etch into the surface of a master plate for nanoimprinting, which is exactly what we need to make patterned media for higher capacity disk drives.”

Now Ellison and his team of graduate students are working together with HGST to see how this process can be implemented in the current manufacturing processes. Their findings were reported in the journal Science.

Is this the farthest we can go with magnetic storage? Well, I wouldn’t worry too much about it, if I were you. Solid State Drives are the next generation of storage mediums, though next generation might not be the best word here since they’ve been commercially available for years, but only recently started to pick up with the public.

Solid state drives are made from silicon microchips and store data electronically instead of magnetically, as spinning hard disk drives or magnetic oxide tape do. Thy’re faster, lighter and a lot more reliable than magnetic hard drives, the only impediment is that they’re currently roughly four times as expensive, but like all things in tech they’ll become reasonable enough for the general public in no time. Say goodbye to your HDD.