Spiders and ants inspire metal that won't sink | Hacker News Reader

Spiders and ants inspire metal that won't sink

rochester.edu

118 pointsdnetesn65 comments

As a child, hanging out by the community pool in the summers, I learned the following trick:

If you can trap and drown a fly, you can then cover the dead fly with salt, which will suck the water out of the fly, and bring the “resurrected” fly back to life.

The relevance here: it is surprisingly difficult to drown a fly, because the weird hairs around their bodies create an air bubble around them, which protects them. A fly in a bubble of air can survive for at least 20 minutes underwater. Released, they will float to the surface inside this bubble and fly away.

Don’t ask how I know.

Similar to funnel web spiders. You have to be careful removing 'dead' ones from a pool as they can survive over 24 hours underwater.

https://australianmuseum.net.au/learn/animals/spiders/funnel...

> australianmuseum.net

Why am I not surprised?

Yup. Everything in Australia looks scary AF, knows how to play dead and kill you.

Especially those drop bears.

There’s a simpler way to resurrect a seemingly dead fly, sometimes used as a magic trick. Put a live fly in the freezer. When it is cold enough it starts to hibernate and will appear to be dead. Just holding it in the palm of your hand gives it enough heat to warm up and come to life again.

Can’t say I condone this, it seems rather cruel.

Cruel? The fly didn't even realize what happened and forgot as soon as it left your palm.

I feel like the "if they don't know what happened it's ok" perspective is a bit of a low bar ethically.

Not just know, have no comprehension of understanding. It's doubtful it registers as pain to them.

I was playing devil's advocate for a bit, there are much crueler things one can imagine. Freezing and unfreezing like this has been the dream in much of sci fi. And it doesn't cause any harm or difference at the end?

Some commenters on reddit are not so hyped by this PR piece.

https://www.reddit.com/r/science/comments/dssixi/inspired_by...

HN has loose posting standards, but /r/science is heavily moderated. They zealously delete comments witn an inch of speculation, but for some reason allow University press releases, whose only purpose is to take a science paper and dress it up in a pile of nonscience for marketing use. I don't understand why the mods there allow it.

> I don't understand why the mods there allow it.

Precisely because it can result in excellent comments like the current top comments on the article.

Providing an opportunity for experts to exercise critical analysis is a good thing and an excellent teaching/learning opportunity.

Great contribution. Key criticism from my standpoint:

  ...The buoyancy provided by superhydrophobicity scales 
  with surface area, while the mass of a ship scales with 
  volume, so this can only ever work for roughly coin-sized 
  objects. ...

lame PR piece.

Yup. Even disregarding the problems mentioned in the linked post, it isn't going to work well for real-world applications.

Fresh or saltwater, any vessel is subject to corrosion and the accumulation of grime (or worse, like barnacles). In the demo video, note that the demonstrator is using gloves and isn't even touching the "coin" directly, but using tweezers.

Thinking about this method, I think that a much better use for the technique could be:

1) either engrave the inner surface of metallic parts in airplanes or spatial stations with a microscopic pattern allowing the recognition ot metal scrapes stolen or found in the sea after an accident (hours count and you could be searching in the wrong area). This could accelerate a lot the identification of the remains and help identifying corpses found next to some metallic part. Many metallic parts are hollow and as long as the pattern is placed in inner surface (inside a tube for example) would not create any problem with dirt, paint or gloss of the final product. That could be a real application.

2) or try to engrave the outer surface to make the airplane surface smoother without losing too much efficience and properties. I assume that this in hands of a competent engineer could reduce a little the noise emited by the airplane.

3) same as point one, but for guns and weapons would be also really useful

In short:

> The [metal floats because they use] bursts of lasers to "etch" the surfaces of metals with intricate micro- and nanoscale patterns that trap air and make the surfaces superhydrophobic, or water repellent.

Neat!

terry pratchett's discworld series had hydrophobic wizards raised on dehydrated water that were so hydrophobic that the air around them could displace large amounts of water allowing for water travel.

Cool. It would be even cooler if they could make an "aerophobic" material so it floats in the air. Put some of it on the bottom side of a skateboard and you have a hoverboard (hopefully!).

It's fun to daydream about, but even if you could somehow warp surface tension to hold bubbles of vacuum against a surface, displacing air gives you less than 1/750th as much lift as displacing water.

Related link: https://www.o-boot.com/en/

s.a. https://en.wikipedia.org/wiki/Vacuum_airship

Not the same principle really as these things float on water rather than in it. Things on water float at the boundary with the lighter air. If you want to do the same thing on air you should do it at the boundary with something else, even lighter.

If you are completely engulfed in air you're like a diver underwater achieving neutral buoyancy, the same kind of thing as a perfectly balanced balloon. So you're floating in air rather than on air.

> Not the same principle really as these things float on water rather than in it.

Huh? Half the article talks about how they maintain buoyancy while submerged and why that's important.

You don't need a boundary, and it wouldn't help you if you did. You still need to displace the same amount of air.

The only way on/in makes a difference is if you have some way to prevent the fluid from going around you. You'd have to be tightly jammed inside a tube for that.

And will not work in the real life, because they are not paying attention to biology, just copying it without understanding the ecological processes.

Anything with tiny pores put on the sea will either be covered in life in weeks, or will need anti-fouling painting to avoid rust and life (distroying the effect), or this pores will be filled with lime and mud in no time. A ship hull that is not easily cleanable and can't be polished is creating many new problems.

I could be wrong but translating this to the real life applications seems really complicated to implement. Specially when you can just create a sealed metal box filled with multiple air cameras or a buoy.

> Anything with tiny pores put on the sea will either be covered in life in weeks

My question with this, is that if an air bubble is formed against the surface of the material and thus the water is not touching the surface.. how does the life inside the water attach itself to the surface which it does not touch?

That’s assuming there’s one perfect & stable air bubble that is never broken?

If something gets into even one pore and starts displacing air, that would be enough to break equilibrium, right?

Marine larvae have legs with strong claws and chaetas and secrete several natural cements. They could just displace or peel the air bubble. Moreover, having tiny pores would grant a stronger grip to the hull against being washed by sea currents and cleaning hoses.

Also in a storm that air bubble will get blown out. Notice how gently they treat it in the video.

I don't understand why you couldn't just cover the surface with a smooth coating, trapping the air inside in a billion little bubbles.

They could put it on planes so the material floats and becomes easier to find in the case of the plane crashing into the sea. Doesn't need to work for long, only long enough for it to be found.

The main issue is that this only works on things that are tiny enough that a micro-layer of surface air can substantially affect their buoyancy. It's a cool trick, and I'm sure it has uses, but it's not going to do a thing for planes and ships. It'd be like trying to float a Buick by tying a party balloon to it.

Sadly is useless even for that. They will not found a silvery small object in a sea full of silvery small fishes and waves. If you really want to have a chance to find something in the sea you need an orange decent-sized buoy at day, or an intermitent light at night.

I wonder if this has applications in the food market. Could you make metal cans/bottles that wouldn't hold their contents? (e.g. a ketchup bottle that poured out the last drop) Would the uneven surface provide a haven for bacteria?

If you want simple hydrophobic properties, just use PTFE coating. It has its limitations but you don't have to wait for commercialization as the tech is pretty mature.

There is also the liquiGlide developed from MIT research https://www.wired.com/2015/07/physics-behind-no-stick-ketchu...

I wonder if PTFE coatings would serve as an effective bottom coat, I've never heard of it being used on sailboats but it seems like an obvious avenue to explore.

The tech. described in TFA sounds like something that would make for an awful bottom coat, since such surfaces tend to promote growth by providing something attachable.

It sounds incredibly toxic, though - Polytetrafluoroethylene.

Would be nicer to just point lasers and the existing cans or glass bottles and be done with it.

The hydrophobic properties of the OP are from a cushion of air. So whatever you're keeping in the bottle shouldn't degrade when exposed to oxygen for that to work.

There's no reason why it'd have to be in air for it to work. Food is regularly packaged with nitrogen or argon to keep it fresh. Google "modified atmosphere packaging" for more.

Is the surface tension of water different when in the presence of different gases?

I hope you use carbon neutral energy for those lasers.

Does it sound incredibly toxic when spelled 'teflon'? It's pretty good on the food-safety front.

But not all good: https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Ecotox...

So there are two main issues.

One is only relevant at hundreds of degrees, so it's a pan problem and not a can/bottle problem.

The other is a separate chemical that's sometimes used in the production, and the solution is simply to not use that chemical.

So not perfect, but pretty good!

> and the solution is simply to not use that chemical

If it were that simple then they would already not be using it

> If it were that simple then they would already not be using it

Yeah, did you read the link? "several manufacturers have entirely discontinued its use"

But also your statement isn't really true as a general rule. Sometimes it's very straightforward to avoid an ingredient but it costs half a penny extra.

If you call it Teflon, would you be less scared of the name?

No. Teflon manufacture has led to long-term contamination of waterways, plus illness caused be workers exposure ("teflon flu").

So I would prefer nanoengineering to manipulate surface tension.

> So I would prefer nanoengineering to manipulate surface tension.

Nanotoxicity is a very poorly understood field and any nanomaterials are at the very least likely to flake away bits that are similar to asbestos.

This changes nothing for ships. Ships float because they already "trap" a huge "air bubble" inside because of their hull shape. Making the hull walls repel water might lower the drag but won't change buoyancy.

And after a week these etchings will be covered by sealife and won't work anyway.

The theory here is that if the hull was punctured with a cannon-ball sized hole, then the one that repels water may still be filled with that air bubble.

I do see your point. This is easier to envision on a smaller scale in production, however. In theory, if it works for a small vessel, it should also work for a larger one. Although I don't see large sea-bearing vessels changing any time soon.

Either way, innovation is cool...and it always starts somewhere.

Without knowing much about ship dynamics it sounds suspicious that you could make an unsinkable ship based upon this concept. Isn't the above water mass of the ship held up by the (large) amount of air in the hull? If you punctured the hull (releasing the air) then wouldn't this material have to support the entirety of the ship with the minuscule layer of air bubbles across the surface of the hull? I notice the person's hand pushing the disc down with relative ease so I'd assume its buoyant but not super-buoyant

It’s not the air holding a ship up, it’s the displaced water. Once the weight of displaced water is equivalent to the ship’s weight, it floats.

Another way to think about it is specific weight. Ships have fewer kilograms per cubic meter than water does so they float. When pierced they start filling up with water which makes their specific weight go up and eventually become more kilo per cubic meter than water. At that point the ship sinks.

I think the concept also works with displaced water, those hydrophobic surfaces create air containers that make the whole thing lighter.

But why so complicated? A 10cm metal hull seems much safer than a 5mm opening with hydrophobic coating.

Also with a chamber system ship's can be made pretty robust and almost unsinkable.

Yes, it’s displaced water... So I’m guessing the trapped air bubbles here increase the displacement of the water while only adding the weight of the air? It seems like such a small amount of displacement you’d get from these tiny air bubbles. Then again, those discs look super thin too.

You'd only need as much air volume as you have volume of things heavier than water. A boat sinks because air is displaced by water, increasing the density of the boat. If you make sure the displaceable air runs out before the density of the boat is higher than water it'll never sink.

In practice this is something that's actually done quite a bit. Fill a lot of air spaces in a boat with foam and you get to the point where if your boat fills with water you can simply pull the plug in de bottom of the boat and it will un-sink itself most of the way. You see this for example on small sailboats, the only caveat being you can't be on the boat as it's un-sinking since you'd weigh it down.

That said, seems to me that foam is a lot cheaper and easier than micro-engineering every surface on the boat.

This looks like a novel and not immediately intuitive way of trapping air in a narrow space between two plates of metal. Neat.

There are other ways of trapping air between two pieces of metal.

I wonder how this compares against a sandwich of metal-bubble-wrap-metal. Or with styrofoam, or an injectable foam. It would also float. It would also withstand multiple punctures. I imagine it is cheaper than etching metal.

If this makes it into warships, we can expect torpedos and anti-ship missiles to contain something like laundry detergent that stops the bubbles from forming.

Come to think of it: they better make sure this bubble isn't influenced by some trivial chemicals, otherwise they don't need explosives to sink a ship...

If this tech makes it to industry I suspect it will make it to the inside high performance hydraulics before it makes it to the outside of ships. Those parts are already manufactured to high tolerances and operate in a chemically controlled environment. A little etching somewhere in a pump body or in a key place on an impeller to reduce friction by a percent or two could pay off big time over the life of the device.

Mmmh, you'd need quite a lot of air for your device to be overall lighter than water...

Would be awesome to see this done on a model boat to prove out the concept.

Boats already float

Yeah, but are they made out of ants?

Leininger would like a word with you.

Yes but why not simply a metal honeycomb structure, with air bubbles trapped permanently inside?

Also, an "unsinkable flotation device" can be made out of styrofoam?

Url changed from https://phys.org/news/2019-11-spiders-ants-metal-wont.html, which points to this.

Reply on news.ycombinator.com