Tag Archives: superhydrophobic

Scuba diving flies use bubbles to feed underwater

For most insects, going beneath the water surface would be suicide. But for these flies in California’s Mono Lake, it’s a walk in the park. They use protective air bubbles to protect their bodies using a phenomenon called superhydrophobicity.

Fly divers

A fly in an air bubble. Credits: Floris van Breugel/Caltech.

More than a century ago, as he was traveling through America, Mark Twain discovered an unusual phenomenon at Mono Lake, just to the east of Yosemite National Park. He witnessed large group of black flies dipping into the lake, documenting it in his travel memoir “Roughing It.”

“You can hold them underwater as long as you please — they do not mind it — they are only proud of it. When you let them go, they pop up to the surface as dry as a patent office report.”

What Twain observed wasn’t just a quirk of nature, it was an impressive and complex interaction between the chemicals in the water and those inside the flies, researchers report.

Mono Lake is an unusual place. It’s three times saltier than the ocean and about as basic as ammonia. Yet even this inhospitable environment houses some species, including shrimp-eating black flies. Alkali flies, Ephydra hians live along the shores of the lake and walk underwater, encased in small air bubbles for grazing and to lay eggs. Scientists have been wondering for a long time how they manage this impressive feat and now, they’ve finally found the answer.

Caltech biologist Michael Dickinson teamed up with Floris van Breugel (now at University of Washington) to study these flies, not only because they dive underwater, but also because they are a crucial part of their local ecosystem.

“Mono Lake has a very delicate and unique ecosystem,” says van Breugel. “Conservationists have fought hard to prevent its loss. We were interested in the Mono Lake flies not only because their behavior is so unusual, but because they are a crucial species for the lake’s ecosystem and food web. Mono Lake flies are a crucial component to the local ecosystem, acting as a food source for spiders and for migratory and nesting birds.”

The briny water actually creates the perfect conditions for flies to go beneath the surface. No fish live in Mono Lake, but algae, bacteria, and shrimp are quite abundant. For flies, this means that there are no predators, but there’s a lot of available food. However, flies need to overcome a big obstacle: surface tension.

Surface tension

Surface tension is the property of a fluid to resist an external force, due to the cohesive nature of the water molecules.

It’s hard to directly experiment surface tension with our human bodies — being so big and dense, once we go into the water, we just sink. But for flies, that’s a different story. Flies are so light that they can actually float on water, due to the surface tension. To a fly, water is dense, sticky, and very hard to penetrate and evade. So the blackflies developed two unique adaptations to overcome these problems: they’re very hairy, and they’re covered by a waxy substance that is as repellent as paraffin. This substance makes the flies hydrophobic — it repels water. This allows them to stay dry, making the flies able to defeat the surface tension and escape the water. The hair also helps by repelling the carbonate-rich water, and the flies also have large claws which allows them to crawl underwater rocks while resisting the naturally buoyant force of the bubble.

Dickinson and Bruegel set up an experiment, plunging unfortunate flies into different wet surfaces, testing the blackflies’ ability to escape such environments and comparing them with the performance of other, closely related flies. They found that no other fly has the same ability. Furthermore, when they rinsed the blackflies with a solvent (hexane) to dissolve their wax, they lost their ability to form a superhydrophobic bubble suggesting that the wax is essential in the process.

Researchers believe that many other fly species might have had this ability, but they lost it because there was simply no motivation to keep it. Going underwater is tiring and risky, as fish can easily gulp you out. The one thing which encouraged Lake Mono’s blackflies to continue was the absence of fish.

“It’s not that Mono Lake flies have evolved a new and unique way of remaining hydrophobic–it’s that they’ve amplified the normal tools that most insects use,” says Dickinson. “It’s just a killer gig. There’s nothing underwater to eat you and you have all the food you want. You’ve just got to dive in perhaps the most difficult water in which to stay dry on the planet. They figured it out, and so get to enjoy an extremely unique life history. It’s amazing how the evolution of such small-scale physical and chemical changes can allow an animal to occupy an entirely new ecological niche.

Still, the questions of Why and How still linger. Researchers say their work answers one question but opens up even more.

“We could go in the materials science direction and study the chemistry of the waxes that the insects use,” he says. “But there’s also some really interesting neurobiology–it is such an incredibly weird thing for a fly to deliberately crawl underwater.”

Journal Reference: Floris van Breugel and Michael H. Dickinson. Superhydrophobic diving flies (Ephydra hians) and the hypersaline waters of Mono Lake.  doi: 10.1073/pnas.1714874114

 

Edible coating can empty every last drop of sticky liquids like ketchup, honey or syrup

coating hydrophobic

Credit: ACS

No matter how much you try, there will always be some drops of ketchup stuck to the bottom and walls of the bottle. Same with just about any sticky, gooey liquids like honey or syrup. Not content to live any longer with such nuisance, a team of researchers developed a safe coating derived from natural materials that can effortlessly slide liquids off. Virtually any liquid can be empty from a container layered in this coating.

An elegant solution to a sticky problem

What the Colorado State University researchers essentially did was to develop a superhydrophobic coating — a nanoscopic surface layer that repels water. Examples of such coatings abound in nature where some plants, such as the Lotus leaf, and some insect wings employ it. Artificial superhydrophobic coatings have been made using materials like precipitated calcium carbonate, silica nanocoating or manganese oxide polystyrene.

[panel style=”panel-success” title=”Why some things are sticky” footer=””]Stickiness depends on the interface of two materials. Honey in itself, for instance, isn’t sticky. It might be when it touches your hand, but not on teflon.

There are several reasons why objects can be sticky, or display adhesive properties. One reason is that certain forces, called Van Der Walls forces, occur between the object and your finger. The molecules are attracted to each other, so it takes force to separate the two once they have come in contact.

Another reason can be more mechanical in nature. For example, if an object’s surface is soft and deformable, when pressed against a rough object, it will deform and ooze into cracks and crevices. Now, to separate the two objects requires that either (1) the soft material get pulled out of cracks and crevices, or (2) the soft material has to get torn apart.

A third mechanism can be the formation of new chemical bonds between the adhesive and the substrate. Such adhesives tend to be very powerful, and the adhesion is harder to reverse. Many adhesives rely on more than one mechanism for their properties.
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What’s different in this case is that the coating is 100 percent safe because it was made from carnauba wax and beeswax, two natural FDA-approve edible materials. Previously, the FDA banned three perfluorinated compounds (PFCs) which were used in pizza packaging to keep the food from greasing because they were deemed unsafe.

The researchers tested the superhydrophobic surface with coke, pancake syrup, Lipton tea, Gatorade, ketchup, and water. Each liquid beaded into a sphere which could be rolled off by gravity alone, leaving no trace behind. The same coating was then tested in a real life situation by layering it inside polystyrene cups. The cups were filled with chocolate syrup or honey and again left no trace after the contents were emptied.

The coating breaks when exposed to a harsh or abrassive environment, though, so there’s some room for improvement. Who am I kidding, it looks almost perfect already. Where do I sign up?

Reference: Wei Wang et al. “Superhydrophobic Coatings with Edible Materials.” ACS Appl. Mater. Interfaces 8 (29): 18664–18668. Published: 12-July-2016. DOI: 10.1021/acsami.6b06958

Super hydrophobic surface

Laser-etching pattern turns any metal into a super-hydrophobic surface

A new generation of water-repellent products could be just ahead after researchers at University of Rochester demonstrated an amazing laser technique that etches tiny micro and nano grooves into a metal surface making it super-hydrophobic. As you can notice, the surface becomes so strongly repelled to water than the water molecules literally bounce off until they exit the surface altogether. We’ve seen such demonstrations before, but previous attempts relied on chemical coatings. Because the nano geometrical pattern is etched in the metal, it does not wear off.

Bouncy water molecules

Super hydrophobic surface

Credit: University of Rochester // GIF via Sploid

“The material is so strongly water-repellent, the water actually gets bounced off. Then it lands on the surface again, gets bounced off again, and then it will just roll off from the surface,” said Rochester’s Chunlei Guo , professor of optics.

Previously, Guo and colleagues had used a similar laser-patterning technique that turned metals black. Building-up on this previous research, the team investigated what kind of properties metals would gain if certain intricate patterns of micro- and nanoscale structures were etched with high-power lasers.

Metal surfaces etched this way could be built in aircraft fuselage to reduce drag or built-in the next generation Teflon cookery. Teflon is also hydrophobic, but the difference is that to make water to roll-off a Teflon coated material, you need to tilt the surface to nearly a 70-degree angle before the water begins to slide off. You can make water roll off Guo’s metals by tilting them less than five degrees.

superhydrophobic surface metal

Credit: University of Rochester // GIF via Sploid

Of more practical worth would be implementing it in developing countries to store more water and build more hygienic latrines.

“In these regions, collecting rain water is vital and using super-hydrophobic materials could increase the efficiency without the need to use large funnels with high-pitched angles to prevent water from sticking to the surface,” says Guo. “A second application could be creating latrines that are cleaner and healthier to use.”

The researchers claim because there’s no chemical coating, the hydrophobic layer won’t rob off. But what about dust and other impurities gathering in the tiny etched grooves? According to the team, this isn’t a problem. The surface also  collects dust particles and takes them along for the ride. In tests, ordinary dust from a vacuum cleaner was applied to the surface; with only three drops of water, half of the dust particles were removed. It’s still not certain how expensive hydrophobic metal surfaces would be. Nevertheless, it’s a pretty exciting project.

Findings appeared in the Journal of Applied Physics.

Superhydrophobic surface causes water to jump like a ball

Superhydrophobic surfaces are surfaces that not only don’t get wet, but they actually repel water. This is the so-called lotus effect, named after the superhydrophobic leaves of the lotus plant (as usually, nature’s been doing long before we have). We’ve written time and time again about the amazing achievements in the field of superhydrophobics – and this is no exception.

Repelling water


In a basement lab on Bringham Young University’s campus (BYU), mechanical engineering professor Julie Crockett analyzes water as it bounces off and rolls like a ball. This happens because Crockett and her colleague Dan Maynes created a superhydrophobic sloped channel that  repels the water.

“Our research is geared toward helping to create the ideal super-hydrophobic surface,” Crockett said. “By characterizing the specific properties of these different surfaces, we can better pinpoint which types of surfaces are most advantageous for each application.”

While some research with such surfaces has already reached the shelves with substances that keep your shoes or clothes dry, the two professors want to provide large-scale solutions for society.

The materials exhibit this effect because their surfaces are riddled with micro posts or with ribs and cavities one tenth the size of a human hair. In order to develop these surfaces, researchers used a process similar to photo film development that etches patterns onto CD-sized wafers. They then coated them in a water-resistant film, like Teflon, but that’s just the start of it: in order to improve the materials, they then study the interactions between the water and the surface with high-speed cameras.

Applications… applications everywhere

A few potential applications for such a technology are:

– solar panels that don’t get dirty or clean themselves when water rolls of them. Or why not – even windows.
– hulls of ships and submarines – coating them in superhydrophobic surfaces would cause less drag, increasing the speed and reducing fuel consumption.
– airplanes wings, helping them better resist in cold and humid conditions.
– showers, tubs, toilets – all could be easier to clean.
– rain-proof glasses.
– biomedical devices, such as syringes that deliver fluids to patients.

However, while there’s a myriad of potential applications, their research focuses on cleaner and more efficient energy generation – especially conventional power plants. Most power plants in the world generate energy by burning coal or natural gas, generating gas that rotates a turbine; once that has happened, the steam needs to be condensed to liquid so it can restart the same cycle all over again. If condensers in power plants would be coated in hydrophobic surfaces, the process could be greatly sped up – increasing generating energy faster and more efficiently.

“If you have these surfaces, the fluid isn’t attracted to the condenser wall, and as soon as the steam starts condensing to a liquid, it just rolls right off,” Crockett said. “And so you can very, very quickly and efficiently condense a lot of gas.”

 

The omniphobic material's geometry and close-up structure. (c) Anish Tuteja / University of Michigan

Superomniphobic material can avoid any stain – repels almost any liquid

Scientists have developed a new surface, which they call  “superomniphobic”, that can repel virtually any liquid, even the most troublesome like blood or highly concentrated acids. Their findings brings us a step closer to manufacturing stain-proof, spill-proof clothing, protective garments and other products.

Currently there is a wide range of clothing and garments that are water proof and offer protection against some spills, but even the most expensive and technologically advanced products, be them synthetics to waxed canvas, don’t stand a chance against low-tension liquids like ketchup or oils that soak right up into the fabric.

Superomniphobic surface

Acetic acid and hexylamine droplets bounce off the superomniphobic material.(c) Anish Tuteja / University of Michigan

In a breakthrough, researchers at Scientists at the University of Michigan have developed a superomniphobic surface  that displays extreme repellency to two families of liquids—Newtonian and non-Newtonian liquids.  Newtonian liquids are most common (water) and are basically liquids whose viscosity remains constant no matter the stress they’re subjected too. While surfaces that repel non-Newtonian fluids have been typically the object of research for most scientists, the Michigan scientists decided to tackle non-Newtonian liquids as well, which include blood, yogurt, gravy, various polymer solutions and a range of other liquids.

“Normally when people talk about superhydrophobic or superomniphobic surfaces, they talk about wetting, which is a measure of the shape that droplets make on the surface and their contact angles,’ says Sergiy Minko, who researches smart polymer materials at Clarkson University in Potsdam, US.

The omniphobic material's geometry and close-up structure. (c) Anish Tuteja / University of Michigan

The omniphobic material’s geometry and close-up structure. (c) Anish Tuteja / University of Michigan

Anish Tuteja and colleagues have developed a surface that repels both Newtonian liquids and oily ones – virtually all liquids easily roll off and bounce on the new surfaces, which makes them ideal for protecting other materials from the effects of chemicals. This was achieved by carefully building the surface such that it has a very low wetting hysteresis – contact angles  of the droplet is the same in both front and rear. This causes the droplet to roll over the surface  without leaking through the surface.

The material is based on a fine stainless steel wire mesh. This is coated with a layer of polymer beads, made from a mixture of polydimethylsiloxane (PDMS) and fluorodecyl polyhedral oligomeric silsesquioxane (POSS). Possible applications for this novel superomniphic surface include  stain-free clothing; spill-resistant, breathable protective wear; surfaces that shrug off microbes like bacteria; and corrosion-resistant coatings.




Findings were reported in the Journal of the American Chemical Society.

via Chemistry World

Droplets

A computer made from water droplets

Droplets

If you thought the computer devised out of soldier crab swarms was cool, wait till you hear what scientists at Aalto University managed to make. In a recently published study, the researchers built a hydrophopic set-up through which they channeled water droplets, and in the process encoded information, practically building a computer.

The researchers used the term “‘superhydrophobic droplet logic” to describe the process through which they stored information. At its core, the Aalto water droplet technique is based on the billiard ball computer model, a computer science textbook algorithm. Interestingly enough, when two water droplets collide with each other on a highly water-repellent surface, they rebound like billiard balls.

Two water repealant channels were devised, made out of a copper surface coated with silver, and chemically modified with a fluorinated compound. Since the formed system is predictable, scientists were able to encode information with water droplets,  with drops on one track representing ones and drops on the other representing zeroes.

“I was surprised that such rebounding collisions between two droplets were never reported before, as it indeed is an easily accessible phenomenon,” says Henrikki Mertaniemi

Concerning its practical applications, while an immediate installation is a bit far off, the researchers involved in the project forsee a use for waterdroplets storage devices in areas where electricity is not available and autonomous, yet simple computing devices are required. Also, were the water droplets to be replaced with reacting chemicals, the systematic logic behind the water droplet computing device could be employed programmable chemical reactor.

Findings were published in the journal Advanced Materials.

Iridescence and superhydrophobicity combined on graphene

Graphene is starting to show its really interesting and exciting properties; recently, scientists have managed to put together two separate properties which usually don’t go together: it is iridescent like a butterfly’s wing, and superhydrophobic, like a rose petal or this material.

The engineered surface could have applications in liquid transportation and analysis, or due to graphene’s remarkable electrical properties, even in electricity. Jian-Nan Wang and coauthors from Jilin University in Changchun, China, achieved these properties by creating a microscopic texture on the graphene oxide’s surface; basically, by using two different lasers, they created an interference pattern that burned a tiny model on the material, resulting in this hue-like appearance. The tiny created grooves form ordered periodic structures which act as diffraction gratings that split light into its basic wavelengths.

Researchers observed that this model also causes graphene to exhibit adhesive superhydrophobicity – a really weird property. When they poured water on the surface, it merged into nearly spherical droplets, which remained just barely in contact although they were remained on the surface even when held upside down – still just barely.

Scientists predict that the combination of these two properties on one surface could have applications in microfluidic devices, for transferring small amounts of liquid in a controlled way. It is becoming more and more clear that graphene is starting to show off some of the remarkable thing it can do.

Superhydrophobic spray means no more washing clothes – among others

Ross Technology Corp, a company that focuses on steel products has created a new product based on the spray known as NeverWet – which aside from being useful, is also pretty cool.

Now, this might not seem particularly interesting, but it has a myriad of applications; it is built from nanoparticles and it is hydrophobic – not only that it stops water from wetting it, but it shoots water right of from the surface on which it was applied.

Even if at first they wanted to apply this technology to steel, they quickly realized the enormous list of applications this can have, from shoes and clothes that wouldn’t require washing any more, to your phone that could become waterproof, or just on stuff that you don’t want bacteria to get on.

This spray will be released as a commercial product next year. Check out this video to see exactly how it works.

Update: The superhydrophobic branch of the company is now called NeverWet, and they are already using  the technology in anti-icing, anti-corrosion, car building, ship building, clothing and even in nuclear facilities.

Spray an even coating on leather or fabric. Here I’m using it to renew the waterproofing on a pair of old boots. Photo: JProvey

Several neutrla people have tested the technology and report great results.

“Equally impressive results arose from my test of the patio furniture seat cushion, which I hosed down in a way that would simulate rainfall. Where it encountered the NeverWet-treated cushion, the water simply beaded up and rolled off. A few days later, I tried again and was satisfied to see no performance change whatsoever”, writes bobvila.

The treatment worked equally well on the outdoor cotton chair cushion. Photo: JProvey