Category Archives: coatings

Material that sheds like a snake when it’s damaged

Truly water-repellent materials are on the horizon. Or, they would be if one tiny problem was solved. According to a May  3, 2017 news item on ScienceDaily, scientists may have come up with that solution,

Imagine a raincoat that heals a scratch by shedding the part of the outer layer that’s damaged. To create such a material, scientists have turned to nature for inspiration. They report in ACS’ journal Langmuir a water-repellant material that molts like a snake’s skin when damaged to reveal another hydrophobic [water-repellent] layer beneath it.

A May 3, 2017 American Chemical Society (ACS) press release (also on EurekAlert), which originated the news item, expands on the theme,

Lotus leaves, water striders and other superhydrophobic examples from nature have inspired scientists to copy their water-repelling architecture to develop new materials. Such materials are often made by coating a substrate with nanostructures, which can be shored up by adding microstructures to the mix. Superhydrophobic surfaces could be useful in a range of applications including rain gear, medical instruments and self-cleaning car windows. But most of the prototypes so far haven’t been strong enough to stand up to damage by sharp objects. To address this shortcoming, Jürgen Rühe and colleagues again found a potential solution in nature — in snake and lizard skins.

The researchers stacked three layers to create their material: a water-repellant film made with poly-1H,1H,2H,2H-perfluorodecyl acrylate (PFA) “nanograss” on the top, a water-soluble polymer in the middle and a superhydrophobic silicon nanograss film on the bottom. Nanograss consists of tiny needle-like projections sticking straight up. The team scratched the coating and submerged the material in water, which then seeped into the cut and dissolved the polymer. The top layer then peeled off like molted skin and floated away, exposing the bottom, water-repellant film. Although further work is needed to strengthen the top coating so that a scratch won’t be able to penetrate all three layers, the researchers say it offers a new approach to creating self-cleaning and water-repellant materials.

The authors acknowledge support from the German Federal Ministry of Education and Research (BMBF) and VDI/VDE/IT GmbH through project NanoTau.

Here’s a video demonstrating the concept,

Published on May 2, 2017

Scientists turn to snakes and lizards for inspiration to create a new material that sheds its outer layer when scratched.

Finally, a link to and a citation for the paper,

Molting Materials: Restoring Superhydrophobicity after Severe Damage via Snakeskin-like Shedding by Roland Hönes, Vitaliy Kondrashov, and Jürgen Rühe. Langmuir, Article ASAP DOI: 10.1021/acs.langmuir.7b00814 Publication Date (Web): April 14, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Adding melanin to make foams and fabrics stronger

Melanin does not have a reputation as a strengthening agent so why these scientists tested it for that purpose is a mystery. From a Nov. 9, 2016 news item on,

Melanin is the natural molecule in animals’ skin, hair and the iris of eyes that gives them color and helps protect them from ultraviolet light. Someday soon, the pigment could be found in unexpected places such as sofa cushions or clothing—but not for its hue. Scientists have found that adding a small amount of melanin to polyurethane makes it far stronger than the material by itself. …

A Nov. 9, 2016 American Chemical Society (ACS) press release (also on EurekAlert), which originated the news item, expands on the theme,

From durable foam seating and insulation to glossy coatings and stretchy textiles, polyurethane is used in a huge range of products. Although already fairly versatile, polyurethane still has room for improvement. To make it more durable, scientists have tried adding fillers, including silica, carbon nanotubes and graphene oxide. But these efforts have often led to the enhancement of only one physical property at a time, such as tensile strength — how hard a material can be pulled before it snaps — but not toughness — how much energy it can absorb without breaking. Mingqing Chen, Weifu Dong and colleagues wanted to try a new approach: adding melanin, a biomolecule increasingly used in various other materials.

The researchers found that polyurethane containing just 2 percent melanin, extracted from the ink sacs of cuttlefish, had improved tensile strength and toughness. These properties were enhanced about 10 fold, increasing from 5.6 megapascals and 33 megajoules per cubic meter in plain polyurethane to 51.5 MPa and 413 MJ/m3, respectively. Polyurethane by itself could stretch 770 percent before breaking, whereas the melanin-infused version stretched 1,880 percent before rupturing.

Here’s a link to and a citation for the paper,

Superior Performance of Polyurethane Based on Natural Melanin Nanoparticles by Yang Wang, Ting Li, Xuefei Wang, Piming Ma, Huiyu Bai, Weifu Dong, Yi Xie, and Mingqing Chen. Biomacromolecules, DOI: 10.1021/acs.biomac.6b01298 Publication Date (Web): October 17, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Nanofiber coating for artificial joints and implants

The researchers have a great image to accompany their research, which fit well with Hallowe’en and the Day of the Dead celebrations taking place around the same time as the research was published.

 A titanium implant (blue) without a nanofiber coating in the femur of a mouse. Bacteria are shown in red and responding immune cells in yellow. Credit: Lloyd Miller/Johns Hopkins Medicine

A titanium implant (blue) without a nanofiber coating in the femur of a mouse. Bacteria are shown in red and responding immune cells in yellow.
Credit: Lloyd Miller/Johns Hopkins Medicine

An Oct. 24, 2016 news item on ScienceDaily announces the research on nanofibers,

In a proof-of-concept study with mice, scientists at The Johns Hopkins University show that a novel coating they made with antibiotic-releasing nanofibers has the potential to better prevent at least some serious bacterial infections related to total joint replacement surgery.

An Oct. 24, 2016 Johns Hopkins Medicine news release (also on EurekAlert), provides further details (Note: Links have been removed),

A report on the study, published online the week of Oct. 24 [2016] in Proceedings of the National Academy of Sciences, was conducted on the rodents’ knee joints, but, the researchers say, the technology would have “broad applicability” in the use of orthopaedic prostheses, such as hip and knee total joint replacements, as well pacemakers, stents and other implantable medical devices. In contrast to other coatings in development, the researchers report the new material can release multiple antibiotics in a strategically timed way for an optimal effect.

“We can potentially coat any metallic implant that we put into patients, from prosthetic joints, rods, screws and plates to pacemakers, implantable defibrillators and dental hardware,” says co-senior study author Lloyd S. Miller, M.D., Ph.D., an associate professor of dermatology and orthopaedic surgery at the Johns Hopkins University School of Medicine.

Surgeons and biomedical engineers have for years looked for better ways —including antibiotic coatings — to reduce the risk of infections that are a known complication of implanting artificial hip, knee and shoulder joints.

Every year in the U.S., an estimated 1 to 2 percent of the more than 1 million hip and knee replacement surgeries are followed by infections linked to the formation of biofilms — layers of bacteria that adhere to a surface, forming a dense, impenetrable matrix of proteins, sugars and DNA. Immediately after surgery, an acute infection causes swelling and redness that can often be treated with intravenous antibiotics. But in some people, low-grade chronic infections can last for months, causing bone loss that leads to implant loosening and ultimately failure of the new prosthesis. These infections are very difficult to treat and, in many cases of chronic infection, prostheses must be removed and patients placed on long courses of antibiotics before a new prosthesis can be implanted. The cost per patient often exceeds $100,000 to treat a biofilm-associated prosthesis infection, Miller says.

Major downsides to existing options for local antibiotic delivery, such as antibiotic-loaded cement, beads, spacers or powder, during the implantation of medical devices are that they can typically only deliver one antibiotic at a time and the release rate is not well-controlled. To develop a better approach that addresses those problems, Miller teamed up with Hai-Quan Mao, Ph.D., a professor of materials science and engineering at the Johns Hopkins University Whiting School of Engineering, and a member of the Institute for NanoBioTechnology, Whitaker Biomedical Engineering Institute and Translational Tissue Engineering Center.

Over three years, the team focused on designing a thin, biodegradable plastic coating that could release multiple antibiotics at desired rates. This coating is composed of a nanofiber mesh embedded in a thin film; both components are made of polymers used for degradable sutures.

To test the technology’s ability to prevent infection, the researchers loaded the nanofiber coating with the antibiotic rifampin in combination with one of three other antibiotics: vancomycin, daptomycin or linezolid. “Rifampin has excellent anti-biofilm activity but cannot be used alone because bacteria would rapidly develop resistance,” says Miller. The coatings released vancomycin, daptomycin or linezolid for seven to 14 days and rifampin over three to five days. “We were able to deploy two antibiotics against potential infection while ensuring rifampin was never present as a single agent,” Miller says.

The team then used each combination to coat titanium Kirschner wires — a type of pin used in orthopaedic surgery to fix bone in place after wrist fractures — inserted them into the knee joints of anesthetized mice and introduced a strain of Staphylococcus aureus, a bacterium that commonly causes biofilm-associated infections in orthopaedic surgeries. The bacteria were engineered to give off light, allowing the researchers to noninvasively track infection over time.

Miller says that after 14 days of infection in mice that received an antibiotic-free coating on the pins, all of the mice had abundant bacteria in the infected tissue around the knee joint, and 80 percent had bacteria on the surface of the implant. In contrast, after the same time period in mice that received pins with either linezolid-rifampin or daptomycin-rifampin coating, none of the mice had detectable bacteria either on the implants or in the surrounding tissue.

“We were able to completely eradicate infection with this coating,” says Miller. “Most other approaches only decrease the number of bacteria but don’t generally or reliably prevent infections.”

After the two-week test, each of the rodents’ joints and adjacent bones were removed for further study. Miller and Mao found that not only had infection been prevented, but the bone loss often seen near infected joints — which creates the prosthetic loosening in patients — had also been completely avoided in animals that received pins with the antibiotic-loaded coating.

Miller emphasized that further research is needed to test the efficacy and safety of the coating in humans, and in sorting out which patients would best benefit from the coating — people with a previous prosthesis joint infection receiving a new replacement joint, for example.

The polymers they used to generate the nanofiber coating have already been used in many approved devices by the U.S. Food and Drug Administration, such as degradable sutures, bone plates and drug delivery systems.

Here’s a link to and a citation for the paper,

Polymeric nanofiber coating with tunable combinatorial antibiotic delivery prevents biofilm-associated infection in vivo by Alyssa G. Ashbaugh, Xuesong Jiang, Jesse Zheng, Andrew S. Tsai, Woo-Shin Kim, John M. Thompson, Robert J. Miller, Jonathan H. Shahbazian, Yu Wang, Carly A. Dillen, Alvaro A. Ordonez, Yong S. Chang, Sanjay K. Jain, Lynne C. Jones, Robert S. Sterling, Hai-Quan Mao, and Lloyd S. Miller. PNAS [Proceedings of the National Academy of Sciences] 2016 doi: 10.1073/pnas.1613722113 Published ahead of print October 24, 2016

This paper is behind a paywall.

Ocean-inspired coatings for organic electronics

An Oct. 19, 2016 news item on describes the advantages a new coating offers and the specific source of inspiration,

In a development beneficial for both industry and environment, UC Santa Barbara [University of California at Santa Barbara] researchers have created a high-quality coating for organic electronics that promises to decrease processing time as well as energy requirements.

“It’s faster, and it’s nontoxic,” said Kollbe Ahn, a research faculty member at UCSB’s Marine Science Institute and corresponding author of a paper published in Nano Letters.

In the manufacture of polymer (also known as “organic”) electronics—the technology behind flexible displays and solar cells—the material used to direct and move current is of supreme importance. Since defects reduce efficiency and functionality, special attention must be paid to quality, even down to the molecular level.

Often that can mean long processing times, or relatively inefficient processes. It can also mean the use of toxic substances. Alternatively, manufacturers can choose to speed up the process, which could cost energy or quality.

Fortunately, as it turns out, efficiency, performance and sustainability don’t always have to be traded against each other in the manufacture of these electronics. Looking no further than the campus beach, the UCSB researchers have found inspiration in the mollusks that live there. Mussels, which have perfected the art of clinging to virtually any surface in the intertidal zone, serve as the model for a molecularly smooth, self-assembled monolayer for high-mobility polymer field-effect transistors—in essence, a surface coating that can be used in the manufacture and processing of the conductive polymer that maintains its efficiency.

An Oct. 18, 2016 UCSB news release by Sonia Fernandez, which originated the news item, provides greater technical detail,

More specifically, according to Ahn, it was the mussel’s adhesion mechanism that stirred the researchers’ interest. “We’re inspired by the proteins at the interface between the plaque and substrate,” he said.

Before mussels attach themselves to the surfaces of rocks, pilings or other structures found in the inhospitable intertidal zone, they secrete proteins through the ventral grove of their feet, in an incremental fashion. In a step that enhances bonding performance, a thin priming layer of protein molecules is first generated as a bridge between the substrate and other adhesive proteins in the plaques that tip the byssus threads of their feet to overcome the barrier of water and other impurities.

That type of zwitterionic molecule — with both positive and negative charges — inspired by the mussel’s native proteins (polyampholytes), can self-assemble and form a sub-nano thin layer in water at ambient temperature in a few seconds. The defect-free monolayer provides a platform for conductive polymers in the appropriate direction on various dielectric surfaces.

Current methods to treat silicon surfaces (the most common dielectric surface), for the production of organic field-effect transistors, requires a batch processing method that is relatively impractical, said Ahn. Although heat can hasten this step, it involves the use of energy and increases the risk of defects.

With this bio-inspired coating mechanism, a continuous roll-to-roll dip coating method of producing organic electronic devices is possible, according to the researchers. It also avoids the use of toxic chemicals and their disposal, by replacing them with water.

“The environmental significance of this work is that these new bio-inspired primers allow for nanofabrication on silicone dioxide surfaces in the absence of organic solvents, high reaction temperatures and toxic reagents,” said co-author Roscoe Lindstadt, a graduate student researcher in UCSB chemistry professor Bruce Lipshutz’s lab. “In order for practitioners to switch to newer, more environmentally benign protocols, they need to be competitive with existing ones, and thankfully device performance is improved by using this ‘greener’ method.”

Here’s a link to and a citation for the research paper,

Molecularly Smooth Self-Assembled Monolayer for High-Mobility Organic Field-Effect Transistors by Saurabh Das, Byoung Hoon Lee, Roscoe T. H. Linstadt, Keila Cunha, Youli Li, Yair Kaufman, Zachary A. Levine, Bruce H. Lipshutz, Roberto D. Lins, Joan-Emma Shea, Alan J. Heeger, and B. Kollbe Ahn. Nano Lett., 2016, 16 (10), pp 6709–6715
DOI: 10.1021/acs.nanolett.6b03860 Publication Date (Web): September 27, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall but the scientists have made an illustration available,

An artist's concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

An artist’s concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

Achieving ultra-low friction without oil

Oiled gears as small parts of large mechanism Courtesy: Georgia Institute of Technology

Oiled gears as small parts of large mechanism Courtesy: Georgia Institute of Technology

Those gears are gorgeous, especially in full size; I will be giving a link to a full size version in a bit. Meanwhile, an Oct. 11, 2016 news item on Nanowerk makes an announcement about ultra-low friction without oil,

Researchers at Georgia Institute of Technology [Georgia Tech; US] have developed a new process for treating metal surfaces that has the potential to improve efficiency in piston engines and a range of other equipment.

The method improves the ability of metal surfaces to bond with oil, significantly reducing friction without special oil additives.

“About 50 percent of the mechanical energy losses in an internal combustion engine result from piston assembly friction. So if we can reduce the friction, we can save energy and reduce fuel and oil consumption,” said Michael Varenberg, an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering.

An Oct. 5, 2016 Georgia Tech news release (also on EurekAlert but dated Oct. 11, 2016), which originated the news item, describes the research in more detail,

In the study, which was published Oct. 5 [2016] in the journal Tribology Letters, the researchers at Georgia Tech and Technion – Israel Institute of Technology tested treating the surface of cast iron blocks by blasting it with mixture of copper sulfide and aluminum oxide. The shot peening modified the surface chemically that changed how oil molecules bonded with the metal and led to a superior surface lubricity.

“We want oil molecules to be connected strongly to the surface. Traditionally this connection is created by putting additives in the oil,” Varenberg said. “In this specific case, we shot peen the surface with a blend of alumina and copper sulfide particles.  Making the surface more active chemically by deforming it allows for replacement reaction to form iron sulfide on top of the iron. And iron sulfides are known for very strong bonds with oil molecules.”

Oil is the primary tool used to reduce the friction that occurs when two surfaces slide in contact. The new surface treatment results in an ultra-low friction coefficient of about 0.01 in a base oil environment, which is about 10 times less than a friction coefficient obtained on a reference untreated surface, the researchers reported.

“The reported result surpasses the performance of the best current commercial oils and is similar to the performance of lubricants formulated with tungsten disulfide-based nanoparticles, but critically, our process does not use any expensive nanostructured media,” Varenberg said.

The method for reducing surface friction is flexible and similar results can be achieved using a variety of processes other than shot peening, such as lapping, honing, burnishing, laser shock peening, the researchers suggest. That would make the process even easier to adapt to a range of uses and industries. The researchers plan to continue to examine that fundamental functional principles and physicochemical mechanisms that caused the treatment to be so successful.

“This straightforward, scalable pathway to ultra-low friction opens new horizons for surface engineering, and it could significantly reduce energy losses on an industrial scale,” Varenberg said. “Moreover, our finding may result in a paradigm shift in the art of lubrication and initiate a whole new direction in surface science and engineering due to the generality of the idea and a broad range of potential applications.”

Here’s a link to and a citation for the paper,

Mechano-Chemical Surface Modification with Cu2S: Inducing Superior Lubricity by Michael Varenberg, Grigory Ryk, Alexander Yakhnis, Yuri Kligerman, Neha Kondekar, & Matthew T. McDowell. Tribol Lett (2016) 64: 28. doi:10.1007/s11249-016-0758-8 First online: Oct. 5, 2016

This paper is behind a paywall.

Nanotechnology-enhanced roads in South Africa and in Kerala, India

It’s all about road infrastructure in these two news bits.

Road building and maintenance in sub-Saharan Africa

A July 7, 2016 news item on describes hopes that nanotechnology-enabled products will make roads easier to build and maintain,

The solution for affordable road infrastructure development could lie in the use of nanotechnology, according to a paper presented at the 35th annual Southern African Transport Conference in Pretoria.

The cost of upgrading, maintaining and rehabilitating road infrastructure with limited funds makes it impossible for sub-Saharan Africa to become competitive in the world market, according to Professor Gerrit Jordaan of the University of Pretoria, a speaker at the conference.

The affordability of road infrastructure depends on the materials used, the environment in which the road will be built and the traffic that will be using the road, explained Professor James Maina of the department of civil engineering at the University of Pretoria.

Hauling materials to a construction site contributes hugely to costs, which planners try to minimise by getting materials closer to the site. But if there aren’t good quality materials near the site, another option is to modify poor quality materials for construction purposes. This is where nanotechnology comes in, he explained.

For example, if the material is clay soil, it has a high affinity to water so when it absorbs water it expands, and when it dries out it contracts. Nanotechnology can make the soil water repellent. “Essentially, nanotechnology changes the properties to work for the construction process,” he said.

These nanotechnology-based products have been used successfully in many parts of the world, including India, the USA and in the West African region.

There have also been concerns about road building and maintenance in Kerala, India.

Nanotechnology for city roads in Kochi

A March 23, 2015 news item in the Times of India describes an upcoming test of a nanotechnology-enabled all weather road,

Citizens can now look forward to better roads with the local self-government department planning to use nanotechnology to construct all-weather roads.

For the district trial run, the department has selected a 300-metre stretch of a panchayat road in Edakkattuvayal panchayat. The trial would experiment with nanotechnology to build moisture resistant, long-lasting and maintenance-free roads.

“Like the public, the department is also fed up with the poor condition of roads in the state. Crores of rupees are spent every year for repairing and resurfacing the roads. This is because of heavy rains in the state that weakens the soil base of roads, resulting in potholes that affect the ride-quality of the road surface,” said KT Sajan, assistant executive engineer, LSGD, who is supervising the work.

The nanotechnology has been developed by Zydex Technologies, a Gujarat-headquartered firm. The company’s technology has already been used by major private contract firms that build national highways in India and in other major projects in European and African countries.

Oddly, you can’t find out more about the Zydex products mentioned in the article on its Roads Solution webpage , where you are provided a general description of the technology,

Revolutionary nanotechnology for building moisture resistant, long lasting & maintenance free roads through innovative adaptation of Organosilane chemistry.

Zydex Nanotechnology: A Game Changer

Zydex Nanotechnology has a value propositions for all layers of the road

Zydex Nanotechnology makes the soil moisture resistant, reduces expansiveness and stabilizes the soil to improve its bearing strength manifold. If used with 1% cement, it can stabilize almost any type of soil, by improving the California Bearing Ratio (CBR) to even 100 or above.

Here is the real change in game, as stronger soil bases would now allow optimization of road section thicknesses, potentially saving 10-15% road construction cost.

Prime & Tack coats become 100 % waterproofed, due to penetration and chemical bonding. This also ensures uniform load transfer. And all this at lower residual bitumen.

Chemical bonding between aggregates and asphalt eliminates moisture induced damage of asphaltic layers.

Final comment

I hadn’t meant to wait so long to publish the bit about Kerala’s road but serendipity has allowed me to link it to a piece about South Africa ‘s roads and to note a resemblance to the problems encountered in both regions.

Squeezing out ‘polymer opals’ for smart clothing and more

Researchers at the University of Cambridge have developed a technology for producing ‘polymer opals’ on industrial scales according to a June 3, 2016 news item on Nanowerk (Note: A link has been removed),

Using a new method called Bend-Induced-Oscillatory-Shearing (BIOS), the researchers are now able to produce hundreds of metres of these materials, known as ‘polymer opals’, on a roll-to-roll process. The results are reported in the journal Nature Communications (“Large-scale ordering of nanoparticles using viscoelastic shear processing”).

A June 3, 2016 University of Cambridge press release (also on EurekAlert), which originated the news item, provides more detail (Note: Links have been removed),

Researchers have devised a new method for stacking microscopic marbles into regular layers, producing intriguing materials which scatter light into intense colours, and which change colour when twisted or stretched.

Some of the brightest colours in nature can be found in opal gemstones, butterfly wings and beetles. These materials get their colour not from dyes or pigments, but from the systematically-ordered microstructures they contain.

The team behind the current research, based at Cambridge’s Cavendish Laboratory, have been working on methods of artificially recreating this ‘structural colour’ for several years, but to date, it has been difficult to make these materials using techniques that are cheap enough to allow their widespread use.

In order to make the polymer opals, the team starts by growing vats of transparent plastic nano-spheres. Each tiny sphere is solid in the middle but sticky on the outside. The spheres are then dried out into a congealed mass. By bending sheets containing a sandwich of these spheres around successive rollers the balls are magically forced into perfectly arranged stacks, by which stage they have intense colour.

By changing the sizes of the starting nano-spheres, different colours (or wavelengths) of light are reflected. And since the material has a rubber-like consistency, when it is twisted and stretched, the spacing between the spheres changes, causing the material to change colour. When stretched, the material shifts into the blue range of the spectrum, and when compressed, the colour shifts towards red. When released, the material returns to its original colour. Such chameleon materials could find their way into colour-changing wallpapers, or building coatings that reflect away infrared thermal radiation.

I always like it when there are quotes which seem spontaneous (from the press release),

“Finding a way to coax objects a billionth of a metre across into perfect formation over kilometre scales is a miracle [emphasis mine],” said Professor Jeremy Baumberg, the paper’s senior author. “But spheres are only the first step, as it should be applicable to more complex architectures on tiny scales.”

In order to make polymer opals in large quantities, the team first needed to understand their internal structure so that it could be replicated. Using a variety of techniques, including electron microscopy, x-ray scattering, rheology and optical spectroscopy, the researchers were able to see the three-dimensional position of the spheres within the material, measure how the spheres slide past each other, and how the colours change.

“It’s wonderful [emphasis mine] to finally understand the secrets of these attractive films,” said PhD student Qibin Zhao, the paper’s lead author.

There’s also the commercialization aspect to this work (from the press release),

Cambridge Enterprise, the University’s commercialisation arm which is helping to commercialise the material, has been contacted by more than 100 companies interested in using polymer opals, and a new spin-out Phomera Technologies has been founded. Phomera will look at ways of scaling up production of polymer opals, as well as selling the material to potential buyers. Possible applications the company is considering include coatings for buildings to reflect heat, smart clothing and footwear, or for banknote security [emphasis mine] and packaging applications.

There is a Canadian company already selling its anti-counterfeiting (banknote security) bioinspired technology. It’s called Opalux and it’s not the only bioinspired anti-counterfeiting Canadian technology company, there’s also NanoTech Security which takes its inspiration from a butterfly (Blue Morpho) wing.

Getting back to Cambridge, here’s a link to and a citation for the research team’s paper,

Large-scale ordering of nanoparticles using viscoelastic shear processing by Qibin Zhao, Chris E. Finlayson, David R. E. Snoswell, Andrew Haines, Christian Schäfer, Peter Spahn, Goetz P. Hellmann, Andrei V. Petukhov, Lars Herrmann, Pierre Burdet, Paul A. Midgley, Simon Butler, Malcolm Mackley, Qixin Guo, & Jeremy J. Baumberg. Nature Communications 7, Article number: 11661  doi:10.1038/ncomms11661 Published 03 June 2016

This paper is open access.

There is a video demonstrating the stretchability of their ‘polymer opal’ film

It was posted on YouTube three years ago when the researchers were first successful. It’s nice to see they’ve been successful at getting the technology to the commercialization stage.

A de-icer and a preventative for airplane wings from Rice University

I last mentioned this graphene-based work (from James Tour at Rice University in Texas, US) on de-icing not just airplane wings but also windshields, skyscrapers and more in a Sept. 17, 2014 posting. The latest study indicates the technology could be used as a preventative according to a May 23, 2016 news item on,

Rice University scientists have advanced their graphene-based de-icer to serve a dual purpose. The new material still melts ice from wings and wires when conditions get too cold. But if the air is above 7 degrees Fahrenheit, ice won’t form at all.

A May 23, 2016 Rice University news release (also on EurekAlert), which originated the news item, goes on to describe the work in more detail,

The Rice lab of chemist James Tour gave its de-icer superhydrophobic (water-repelling) capabilities that passively prevent water from freezing above 7 degrees. The tough film that forms when the de-icer is sprayed on a surface is made of atom-thin graphene nanoribbons that are conductive, so the material can also be heated with electricity to melt ice and snow in colder conditions.

The material can be spray-coated, making it suitable for large applications like aircraft, power lines, radar domes and ships, according to the researchers. …

“We’ve learned to make an ice-resistant material for milder conditions in which heating isn’t even necessary, but having the option is useful,” Tour said. “What we now have is a very thin, robust coating that can keep large areas free of ice and snow in a wide range of conditions.”

Tour, lead authors Tuo Wang, a Rice graduate student, and Yonghao Zheng, a Rice postdoctoral researcher, and their colleagues tested the film on glass and plastic.

Materials are superhydrophobic if they have a water-contact angle larger than 150 degrees. The term refers to the angle at which the surface of the water meets the surface of the material. The greater the beading, the higher the angle. An angle of 0 degrees is basically a puddle, while a maximum angle of 180 degrees defines a sphere just touching the surface.

The Rice films use graphene nanoribbons modified with a fluorine compound to enhance their hydrophobicity. They found that nanoribbons modified with longer perfluorinated chains resulted in films with a higher contact angle, suggesting that the films are tunable for particular conditions, Tour said.

Warming test surfaces to room temperature and cooling again had no effect on the film’s properties, he said.

The researchers discovered that below 7 degrees, water would condense within the structure’s pores, causing the surface to lose both its superhydrophobic and ice-phobic properties. At that point, applying at least 12 volts of electricity warmed them enough to retain its repellant properties.

Applying 40 volts to the film brought it to room temperature, even if the ambient temperature was 25 degrees below zero. Ice allowed to form at that temperature melted after 90 seconds of resistive heating.

The researchers found that while effective, the de-icing mode did not remove water completely, as some remained trapped in the pores between linked nanoribbon bundles. Adding a lubricant with a low melting point (minus 61 degrees F) to the film made the surface slippery, sped de-icing and saved energy.

Here’s a link to and a citation for the paper,

Passive Anti-icing and Active Deicing Films by Tuo Wang, Yonghao Zheng, Abdul-Rahman O. Raji, Yilun Li, William K.A. Sikkema, and James M. Tour. ACS Appl. Mater. Interfaces, Just Accepted Manuscript DOI: 10.1021/acsami.6b03060 Publication Date (Web): May 18, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

Extreme water repellency achieved by combining nanostructured surfaces with Leidenfrost effect

Apparently a new twist has been added to the water repellency story. From a May 17, 2016 news item on ScienceDaily,

What do you get if you combine nanotextured ‘Cassie’ surfaces with the Leidenfrost effect? Highly water-repellent surfaces that show potential for developing future self-cleaning windows, windshields, exterior paints and more [sic]

Combining superhydrophobic surfaces with Leidenfrost levitation–picture a water droplet hovering over a hot surface rather than making physical contact with it–has been explored extensively for the past decade by researchers hoping to uncover the holy grail of water-repellent surfaces.

A May 17, 2016 American Institute of Physics news release on EurekAlert, which originated the news item, provides more detail about the work,

In a new twist, a group of South Korean researchers from Seoul National University and Dankook University report an anomalous water droplet-bouncing phenomenon generated by Leidenfrost levitation on nanotextured surfaces in Applied Physics Letters, from AIP Publishing.

“Wettability plays a key role in determining the equilibrium contact angles, contact angle hysteresis, and adhesion between a solid surface and liquid, as well as the retraction process of a liquid droplet impinged on the surface,” explained Doo Jin Lee, lead author, and a postdoctoral researcher in the Department of Materials and Engineering at Seoul National University.

Nonwetting surfaces tend to be created by one of two methods. “First, textured surfaces enable nonwettability because a liquid can’t penetrate into the micro- or nano-features, thanks to air entrapment between asperities on the textured materials,” Lee said.

Or, second, the Leidenfrost effect “can help produce a liquid droplet dancing on a hot surface by floating it on a cushion of its own vapor,” he added. “The vapor film between the droplet and heated surface allows the droplet to bounce off the surface–also known as the ‘dynamic Leidenfrost phenomenon.'”

Lee and colleagues developed a special “nonwetting, nanotextured surface” so they could delve into the dynamic Leidenfrost effect’s impact on the material.

“Our nanotextured surface was verified to be ‘nonwetting’ via thermodynamic analysis,” Lee elaborated. “This analytical approach shows that the water droplet isn’t likely to penetrate into the surface’s nanoholes, which is advantageous for designing nonwetting, water-repellant systems. And the water droplet bouncing was powered by the synergetic combination of the nonwetting surface–often called a ‘Cassie surface’–and the Leidenfrost effect.”

By comparing the hydrophobic surface and nanotextured surface, the group discovered that enhanced water droplet bouncing was created by the combined impact of the Leidenfrost levitation and the nonwetting Cassie state.

“A thermodynamic approach predicts the nonwettability on the nanotextured surface, and a scaling law between the capillary and vapor pressure of the droplet explains the mechanism of the dynamic Leidenfrost phenomenon,” said Lee.

These findings should “be of value for a wide range of research areas, such as the study of nonwetting surfaces by the Leidenfrost effect and nanotextured features, enhanced liquid droplet bouncing, and film boiling of liquid droplets on heated Cassie surfaces,” he added.

Significantly, the group’s work furthers the fundamental understanding of the dynamic Leidenfrost droplet levitation and droplet-bouncing phenomena on hydrophobic and nanoengineered surfaces. This means that it will be useful for developing highly water-repellant surfaces for industrial applications such as self-cleaning windows, windshields, exterior paints, anti-fouling coatings, roof tiles, and textiles in the future.

“Our future work will focus on developing multiscale structures with microscale and nanoscale regularities, and explore the nonwetting characteristics of their surfaces with the dynamic Leidenfrost effect,” Lee noted.

Here’s a link to and a citation for the paper,

Anomalous water drop bouncing on a nanotextured surface by the Leidenfrost levitation by Doo Jin Lee and Young Seok Song.  Appl. Phys. Lett. 108, 201604 (2016);

This paper appears to be open access.