Laser-generated surface structures create extremely water-repellent metals | Hacker News Reader

Laser-generated surface structures create extremely water-repellent metals

rochester.edu

191 pointsZaheer64 comments

A great achievement.

I would like to have seen it dipped. Also demonstrated with contaminated water of some kind, maybe flour & water paste.

He states it would not degrade, but surely expansion and contraction will take a toll on nanoscale etchings, as well as abrasion and acid content of airborne contaminants.

The surface, upon visual inspection in the video looks rough. What happens say if the surface is regularly in contact with skin during a practical application? Does the skin get abraded into the microstructure of the material surface and degrade its hydrophobic properties?

Looks amazing though watching the water spread out and spring back that much. Simply incredible.

Yeah, I'm very curious about the degradation behaviour, especially abrasion.

And Chunlei does it again. I was an undergraduate when he arrived and helped set up the first UHV chamber for his initial tests. Let me just say that not only is he brilliant but he is also about as down to earth a person as you could ever meet. He seriously has no ego, is easy going and has an internal drive that's unbelievable.

If he ever wants to start a company, whomever he reaches out to, fund him.

I would love to learn more about the structure of the patterns etched into the metals. I took a quick look through the links from the article, but didn't find anything with meat. Does anyone have a link?

I'd love to see it under a microscope, or see a visualization of the pattern. Is the strategy to maximize the surface area of an existing hydrophobic material?

Link to the paper [1] (with microscopy images) in the Journal of Applied Physics leads the 3rd paragraph of the article.

[1] http://scitation.aip.org/content/aip/journal/jap/117/3/10.10...

Fantastic, thank you

Shark skin has similar properties. The sharks use it for super efficient swimming, it reduces their drag considerably.

http://www.asknature.org/strategy/038caf2e453c09b3016465cc6c...

Car wash companies will hate this stuff, and wouldn't it be nice if it could be etched into windshields, no more wipers!

Some of the features have sizes comparable to the wavelength of visible light. I would be very, very surprised if you could see clearly through a surface patterned like this.

"Car wash companies will hate this stuff."

Never took you for a limb air headline writer! :)

You still need to wash off the dust, so some sort of wipers are needed still.

When swimming, the drag is pretty minor, most of your energy is spent on the displacement of water. That's true with fish, and with ships and boats.

"As the water bounces off the super-hydrophobic surfaces, it also collects dust particles and takes them along for the ride... Better yet, it remains completely dry."

That requires a sufficient water-to-dust ratio. Driving jeeps in the Congo, or having dust blown up from dunes in a sudden gust, will require wipers. Not to mention pollen.

Couldn't you still have sprayers that would help with this?

Hmm, that's not a bad idea! Current sprayers would obviously be inefficient because they rely on wipers to spread fluid widely over the windshield, but I'm sure that could be changed. (Such as a top pressure-rail for dispensation)

lotus effect

Do hydrophobic materials interact differently with gases as well? What would the air flow be like over a wing made out of a superhydrophobic material like this? Would it facilitate or disrupt airflow, or not matter?

Yes, that's been done:

http://www.lufthansa-technik.com/famos

See sharkskin bit above.

Hydrophobicity alone is only so useful.

Teflon became a thing because it's both hydrophobic and lipophobic. There are lots of hydrophobic surfaces that work very well until you get dirt, finger oils, soap, or just about anything that isn't water-soluble on them. There may also be an issue here with friction damage.

Hopefully the technique here can be adapted to practical products.

The technique is extremely flexible. I'm sure they'll figure out an etching pattern that is both extremely lipophobic and hydrophobic. Only hydrophobia has many applications already.

I wanted to know more about the practical applications of the syperhydrophilic metals (the counter-technology of the one discussed here), and found this video [1] with Chunlei informative.

[1] https://www.youtube.com/watch?v=JtDPsWd6Yqw

I'm looking for superhydrophobic materials for my next car so its easier to keep clean.

Am I twisted when I first thought of non stick, non coated cookware when I saw the title.

Great achievement.

Wouldn't a hydrophobic surface attract oils?

(maybe that's only the case for chemical hydrophobicity rather than structural)

I think this could have a great impact on water vessels. I wonder if they can do the same sort of thing on a fiberglass surface...

It's a good thing the Olympics banned those full-body swimsuits. This would be the next million-dollar suit.

My thoughts exactly... maybe because I'm reading Sail Performance at the moment! Weight, durability and shapability would be important properties vs. the nominal reduction in drag, though.

This is awesome! I look forward to my teflon pans that I don't have to throw away after 6 months because they stop working.

Same!

But for now, baby the shit out of them. Buy one that gets legit amazon reviews for your next one. Hand wash it and mayyybe use a sponge when washing it. Only use wooden, plastic or silicone utensils in it.

If somebody cleans it with a scrubby pad or uses a metal spatula, they get shot/buy you your next pan. :)

I did 2 years on my most recent nonstick pan until my roommate cleaned it with a scrubby pad.

May I recommend iron or copper pans? No sticking, can be used for your whole life. This new structure still looks nice.

Seriously yes - after I figured out how to use and care for cast iron I wondered what the heck made me buy nonstick pans in the first place. The main downsides are the weight of cast iron, or if some clueless person in your house throws it in the sink for a few days.

Avoid Teflon -- it leaches toxic PFOA into food. The ceramic nonstick pans work about as well, and are safe.

What is your source on that?

"Non-stick cookware is not a significant source of exposure." is what cancer.org [0] has to say about Telon and PFOA.

[0] http://www.cancer.org/cancer/cancercauses/othercarcinogens/a...

Personal experience. A few years ago my prostate enlarged relatively suddenly, to the point of making urination difficult. My doctor had no idea why, but it eventually dawned on me that I had recently been eating a lot of scrambled eggs, scrambled in a Teflon-coated skillet. I replaced it with a ceramic nonstick skillet, and the problem went away.

If you want absolute proof an anecdote won't satisfy you, but it's plenty of evidence for me. Look at the cost/risk calculation. The cost of a ceramic pan is on the order of $35; the cost of getting cancer is potentially quite large. There doesn't have to be a very large probability that Teflon causes cancer before it's not worth taking the chance.

That doesn't even begin to prove anything about cancer specifically. If it went away just like that, it wasn't cancer.

What if ceramic pans cause cancer?

Look. It takes science a long time to settle all these questions with rigorous research. In the meantime we all have to make decisions in our lives with imperfect, incomplete information. Dismissing all reports of potential risks until there is incontrovertible proof of danger is foolish; doing so out of some misguided fealty to Science and Progress is arrogant.

Downvote all you want, but you're not going to get me to stop posting anecdotes when I think they're relevant. Yes, their probative value is limited; I even acknowledged this in the post! But it isn't zero, and in a world of limited and often conflicting information, sometimes it's the best we can get.

Ceramics don't break down at temperatures encountered in cooking. Teflon does. The only question is whether the breakdown products are bioactive.

Did you even read the second paragraph?

Skepticism is a valuable thing, but it is not an unerring guide to truth. You need to be less credulous of your skepticism.

6 months? I think you're doing something wrong here. Keep teflon coated material to low temperatures, use plastic/wood/silicone utensils and avoid abrasive cleaning techniques.

Never rapidly cool it off, e.g. by sticking it while still hot under the running cold water. This kills the coating just like that.

Huh. I do this all the time and it doesn't seem to affect it.

>Keep teflon coated material to low temperatures

How exactly do you cook with it then?

https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety

"While PTFE is stable and nontoxic at lower temperatures, it begins to deteriorate after the temperature of cookware reaches about 260 °C (500 °F), and decomposes above 350 °C (662 °F).

…

Meat is usually fried between 204 and 232 °C (399 and 450 °F), and most oils start to smoke before a temperature of 260 °C (500 °F) is reached, but there are at least two cooking oils (refined safflower oil and avocado oil) that have a higher smoke point than 260 °C (500 °F). Empty cookware can also exceed this temperature when heated."

This is a pretty big design flaw for someone like me who loves putting a good sear on steak. Good thing cast iron is fairly cheap...

Did you have some implicit expectation that you could heat it for an arbitrary amount of time, at full power, and it would just be fine? Almost all of the spot checking I just did shows temperature warnings / upper limits of around 450 degrees F for non-stick pans, right on their packaging.

Also, equivalently-sized cast iron pans are almost always cheaper than their quality non-stick (i.e. Calphalon) counterparts, and you can restore them if you jack up the seasoning on them.

Did you reply to the wrong comment?

The comment you reply to doesn't complain about their use of teflon (a complaint you imply in your first paragraph) and they praise the cheapness of cast iron (which you repeat with an 'also' in your second paragraph, the 'also' makes it look like you are trying to correct their understanding of the relative situation).

You seem to be agreeing with my comment 100%, but taking a tone that implies some sort of correction.

>Did you have some implicit expectation that you could heat it for an arbitrary amount of time, at full power, and it would just be fine?

You make it sound so unreasonable to put a chunk of metal on the hot thing and wait for it to fully heat.

Don't let the oil evaporate.

Instead you can worry about nanoscopic metal particles detatching from the pan surface and embedding in your food which you then ingest...

I wonder if it would be any worse than cooking on cast iron.

When I went to college and moved in a dorm I got a really good teflon coated pan from my parents. It's still works fine and it's 6 years old now. I even lent it to other guys in the dorm and I wasn't extremely cautious with it. I dealt with shitty pans too though. I think the quality of Teflon coatings could be extremely varying .

I'd expect pans made with this new technique to be as delicate as Teflon, if not more so. Those laser-etched ridges are quite tiny, and if you scratched the pan with a piece of metal, you'd probably wear away the ridges very quickly, creating localized areas of non-hydrophobia.

I wonder what sort of metals this process would work with effectively and whether surfaces can be reprocessed over time.

Honest question, would steel rust just by liquid water, or vapor and oxigen in the air will make it rust eventually?

Water vapor in the form of humidity is sufficient to initiate the rusting process.

Most questions along this line are addressed on this page:

https://van.physics.illinois.edu/qa/listing.php?id=485

Note that if you try to avoid the formation of rust by submerging your steel in water, thinking that will remove the oxidative air component, you run into corrosion issues unless you are submerging in a tank of constantly refreshed distilled water.

I was hoping to see the drop size decreased to the point where it no longer was repelled.

This specifically repel water, or can it repel any liquid?

Generally, hydrophobic substances won't repel nonpolar substances such as oil.

http://en.wikipedia.org/wiki/Hydrophobic_effect

Awesome. Looking forward for a finally lipophobic smartphone. In fact, in the future all surfaces of consumer electronics and other stuff should be superhydrophobic.

I think there are far better ways to do this on a small object of limited lifespan like a smartphone, not to mention that metal is not an ideal way to make a smartphone. You can use it some surfaces, but at some point you'll need plastic and glass.

"I think there are far better ways to do this on a small object of limited lifespan like a smartphone"

Namely?

Simple hydrophobic coating. It wears out eventually, but by the time it does your device is already gathering dust in a drawer.

Won't it create issues with the smartphone slipping out of your hands way too easily?

Nope.

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