Hydrophobic

"Hydrophobic water"

This liquid is water mixed with aerogel powder (I’m going to do a post on aerogel next as it really is awesome). The membrane of the liquid has some hydrophobic qualities that cause the droplets of water to repel each other and not plop back together.

"For anyone with any slight interest in biology, this is how your cells stay separate. The lipid membranes essentially work the same way, making hydrophobic force between the water content inside and outside the cell."

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A shoe Coated in Hydrophobic Material! I tried posting an awesome gif a few days ago of something else to do with hydrophobic material, but for some reason it didn’t work, so this will have to do. Sorry :(

But anyway - The molecules that coat this shoe are Hydrophobic, that means that they basically ‘repel’ water molecules, while we are only just mastering this, nature developed it billions of years ago - Our cell walls are also made of molecules with similar properties!

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Fire ants floating on water in a ‘raft’

Ants have exoskeletons that are naturally hydrophobic, or water repellant. A single ant can walk on water because of the buoyancy of the air bubbles trapped next to its body, and the water’s own surface tension. However, when thousands of ants stand on top of each other, their multiplied weight should cause them to sink. But for years, biologists have observed fire ant colonies floating down flood plains and rivers in their native South America.

Ants float as a group because they can harness the power of nearby air bubbles. Grasping each other’s mandibles or front legs with a force 400 times their body weight, the ants are able to trap small pockets of air between them — like a group floatation device.

The bottom layer of ants rests on top of the water’s surface, and others pile on above them. Even when they do get submerged, the pockets of air bring them back to the surface quickly — and allow them to breathe. When they get submerged, the ants flex their muscles in unison to form a tighter weave. In the top gif if you look at where the water meets the side of the tank you’ll be able to see the meniscus (skin) of the water stretching as the ants are forced down.

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MIT researchers have unraveled exactly how water birds like ducks and cormorants keep dry when diving in up to 100 feet of water. The secret is a combination of water-repelling oil the birds spread on their feathers during preening and the tightly interlocking structure of the feather’s barbs and barbules.

By testing and modeling the action of water on a feather, they were able to see that the bird’s plumage doesn’t totally repel the liquid and can actually get wet when immersed. But the bird’s preening oil increases the energy needed for water to wet the feather. When the animal leaves the water, the wetting is reversed and the water is ejected off the feather.

"If a feather gets wet, there is no need for it to dry out, in the traditional sense of evaporation,” says Robert Cohen, a chemical engineering professor on the research team. “It can dry by directly ejecting the water from its structure, as the pressure is reduced as it comes back up from its dive.” 

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The Brazilian pygmy gecko has hydrophobic skin that water cannot penetrate. The gecko is also super small and lightweight, maxing out at about an inch long. Being tiny and water repellant, it is virtually unsinkable and can sit right on the surface of water.

To see it in action, check out this awesome David Attenborough clip from the Life series.

Images: Luiz Felipe Amui, Thierry Montford

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What Some Can Do With A Little Tension

These striking images of an insect that walks on the surface of water come from the lab of John Bush, an MIT applied mathematics professor. Bush studies fluid dynamics, focusing his science—and the art that often comes from it—on surface tension.

Visualized in the pictures above is the movement of the water strider, a bug that, according to Bush, stands on water through “surface tension force generated by curvature of the free surface.” It propels itself across the surface by rowing hydrophobic legs, which transfer momentum to the water by deforming the film-like surface and shedding fluid vortices as seen in these pictures. Click here to see a larger version of the top picture, which graced the cover of the journal Nature several years ago. Read the paper that describes the physics of water strider motion here.

The lab showed the vortices by floating Thymol Blue, a dye that is insoluble in water and is often used as a pH indicator, on the water’s surface.

We’ve featured work from the Bush lab before. Check out this story to see how you can play with surface tension to make fun cocktail boats driven by alcohol.

All images courtesy David Hu, Brian Chan & John Bush/MIT.

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Neverwet arrives in stores

Awhile back, we wrote about Neverwet, a superhydrophobic coating, that can be used on any surfaces. Now it’s available in Home Depot stores in North America. More from Lancaster Online:

The transition from laboratory wonder to consumer product was made possible by a licensing agreement with Rust-Oleum. NeverWet agreed to let Rust-Oleum manufacture and distribute the product in North America in return for a royalty payment for every can sold. The amount of payment was not disclosed. At Home Depot, Rust-Oleum NeverWet includes two spray cans — a base coat and a top coat — that can cover 10 to 15 square feet. Retailing for $19.97, Rust-Oleum NeverWet will begin appearing over the next few weeks at stores other than Home Depot here and nationwide. “This is a game changer,” said Jim Stinner, vice president of marketing for Rust-Oleum. “Everyone is going to want to try it out.” 

// Leave a message, if you would like to send us a bottle.

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