Fighting ice at the nano level – a promise for improved safety

This is a really neat discovery. As we all know, ice is a big killer and safety hazard, especially on airplanes. This new material prevents supercooled droplets from freezing, sticking, and accumulating.- Anthony

From Harvard: Breaking the ice before it begins

Nanostructured materials repel water droplets before they have a chance to freeze

Sequential images of ice layer removal from hydrophilic Al, fluorinated hydrophobic Si, and microstructured fluorinated Si (SHS). Note the supercooled droplet bounces right off without sticking.

Cambridge, Mass., November 12, 2010 – Engineers from Harvard University have designed and demonstrated ice-free nanostructured materials that literally repel water droplets before they even have the chance to freeze.

The finding, reported online in ACS Nano on November 9th, could lead to a new way to keep airplane wings, buildings, powerlines, and even entire highways free of ice during the worst winter weather. Moreover, integrating anti-ice technology right into a material is more efficient and sustainable than conventional solutions like chemical sprays, salt, and heating.

A team led by Joanna Aizenberg, Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) and a Core Member of the Wyss Institute for Biologically Inspired Engineering at Harvard, focused on preventing rather than fighting ice buildup.

“We wanted to take a completely different tact and design materials that inherently prevent ice formation by repelling the water droplets,” says Aizenberg. “From past studies, we also realized that the formation of ice is not a static event. The crucial approach was to investigate the entire dynamic process of how droplets impact and freeze on a supercooled surface.”

For initial inspiration, the researchers turned to some elegant solutions seen in nature. For example, mosquitos can defog their eyes, and water striders can keep their legs dry thanks to an array of tiny bristles that repel droplets by reducing the surface area each one encounters.

“Freezing starts with droplets colliding with a surface,” explains Aizenberg. “But very little is known about what happens when droplets hit surfaces at low temperatures.”

To gain a detailed understanding of the process, the researchers watched high-speed videos of supercooled droplets hitting surfaces that were modeled after those found in nature. They saw that when a cold droplet hits the nanostructured surface, it first spreads out, but then the process runs in reverse: the droplet retracts to a spherical shape and bounces back off the surface before ever having a chance to freeze.

By contrast, on a smooth surface without the structured properties, a droplet remains spread out and eventually freezes.

“We fabricated surfaces with various geometries and feature sizes—bristles, blades, and interconnected patterns such as honeycombs and bricks—to test and understand parameters critical for optimization,” says Lidiya Mishchenko, a graduate student in Aizenberg’s lab and first author of the paper.

The use of such precisely engineered materials enabled the researchers to model the dynamic behavior of impacting droplets at an amazing level of detail, leading them to create a better design for ice-preventing materials.

Another important benefit of testing a wide variety of structures, Mishchenko adds, was that it allowed the team to optimize for pressure-stability. They discovered that the structures composed of interconnected patterns were ideally suited for stable, liquid-repelling surfaces that can withstand high-impact droplet collisions, such as those encountered in driving rain or by planes in flight.

The nanostructured materials prevent the formation of ice even down to temperatures as low as 󈞅 to 󈞊 degrees Celsius. Below that, due to the reduced contact area that prevents the droplets from fully wetting the surface, any ice that forms does not adhere well and is much easier to remove than the stubborn sheets that can form on flat surfaces.

“We see this approach as a radical and much needed shift in anti-ice technologies,” says Aizenberg. “The concept of friction-free surfaces that deflect supercooled water droplets before ice nucleation can even occur is more than just a theory or a proof-of-principle experiments. We have begun to test this promising technology in real-world settings to provide a comprehensive framework for optimizing these robust ice-free surfaces for a wide range of applications, each of which may have a specific set of performance requirements.”

In comparison with traditional ice prevention or removal methods like salting or heating, the nanostructured materials approach is efficient, non-toxic, and environmentally friendly. Further, when chemicals are used to de-ice a plane, for example, they can be washed away into the environment and their disposal must be carefully monitored. Similarly, salt on roads can lead to corrosion and run-off problems in local water sources.

The researchers anticipate that with their improved understanding of the ice forming process, a new type of coating integrated directly into a variety of materials could soon be developed and commercialized.

###

In addition to Aizenberg, who is also the Susan S. and Kenneth L. Wallach Professor at the Radcliffe Institute for Advanced Study and a Professor of Chemistry and Chemical Biology at Harvard, and Mishchenko, the co-authors of the paper included Benjamin Hatton and Vaibhav Bahadur, both at SEAS and Wyss, and Ashley Taylor and Tom Krupenkin, both at the University of Wisconsin-Madison.

The researchers acknowledge L. Stirling and A. Grinthal for their valuable contribution and funding from DARPA (Award Number HR0011-08-C-0114); the Wyss Institute for Biologically Inspired Engineering at Harvard University; and the U.S. Department of Homeland Security (DHS) Scholarship and Fellowship Program.

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61 thoughts on “Fighting ice at the nano level – a promise for improved safety

  1. “The concept of friction-free surfaces that deflect supercooled water droplets before ice nucleation can even occur is more than just a theory or a proof-of-principle experiments.”
    Pretty cool stuff, but I don’t think I like the idea of friction-free highways. That’s what they’re trying to prevent, right? 😉

  2. “We wanted to take a completely different tact and design materials that inherently prevent ice formation by repelling the water droplets,” says Aizenberg.

    It might be tactless of me to point out that the word that should have been used is “tack,” and derives from the days of sailing ships, but I guess I will.

  3. Don’t have time to comment much now but as one who has fought that natural ice factory- the Cascades of Oregon and Washington, and the Blue mountains of NE
    Oregon (which is in my opinion as bad,under certain conditions,) in various twin
    Cessna and Piper shaped ice sculptures, this is a big deal…

  4. The use of this wing material has real world applications because the risk of flying planes with ice on the wings can be quantified. A certain amount of too much ice on the wings will bring a plane down and kill people. That a measurable quantity in volume of ice can be measured and tested to be the maximum a plane can handle under various conditions before it falls from the sky and kills people is measurable.
    The amount of money to be spent on a preventative device for air planes may be justified in places like Alaska but would be ridiculous spending the money on planes that only fly in the Caribbean.
    Quantifying the dangers of CO2 causing catastrophic global warming to justify spending 1 trillion dollars a year in the carbon trading market has not been done. Before I spend that kind of money on mitigating the risk, first the risk has to be assessed quantitatively.
    We know if we do not inspect and change the brakes on passenger trains ever, we know the train will crash eventually. And we know the odds of the train crashing go up each year that goes by without the proper maintenance. These measurements have been made, the risks assesed and money is allocated accordingly to mitigate the risk.
    Before I spend one trillion dollars on mitigating the risk of man made climate change, I will have the measurable quantifiable assessment of that said risk first, or you ain’t getting that trillion dollars for your imagined problem and your global government scheme. Cause that’s all it is at this point. Period.

  5. Interesting and potentially life saving. I’d rather see public funds spent supporting this type of scientific climate research rather than the dross its been wasted on in the recent past.

  6. Seems like a good thing-but, what is the cost and how do you re-configure the airline fleets now? The best part about this is maybe it will cut down on the pre-takeoff deicing procedures that really slow down traffic at major airports.

  7. “…could lead to a new way to keep airplane wings, buildings, powerlines, and even ENTIRE HIGHWAYS free of ice during the worst winter weather.”
    Say…
    “The concept of FRICTION-FREE surfaces that deflect supercooled water droplets…”
    …what?

  8. A more common and well-known super-hydrophobic surface…..lotus leaf.
    The micro-structure of the leaf surface causes water to be repelled beyond the normal angle provided by surface tension considerations alone. The result? The leaf stays dry and the water beads up and rolls off.
    Some, “waterproof” textiles are already taking advantage of this nanopportunity.

  9. Michael says says November 14, 2010 at 1:48 pm

    The use of this wing material has real world applications because the risk of flying planes with ice on the wings can be quantified. A certain amount of too much ice on the wings will bring a plane down and kill people.

    So, is that one lot of too much ice, or two lots of two much ice, or what?

  10. B-52 says:
    November 14, 2010 at 2:28 pm

    “…could lead to a new way to keep airplane wings, buildings, powerlines, and even ENTIRE HIGHWAYS free of ice during the worst winter weather.”
    Say…
    “The concept of FRICTION-FREE surfaces that deflect supercooled water droplets…”
    …what?

    Just keep your tires dry and you’ll be all set. 🙂

  11. I love this stuff 😀
    Reminds me of the first few years I had Rain-X… I took every opportunity to drive in precipitation, marveling at the way water and ice just flew off the windshield. (Rain-X is a long chain polymer developed for jet aircraft windscreens).

  12. Hah! Now that would save those electricity-generating windmills under icing conditions, wouldn’t it?
    Don’t ask me if that’s worth it.

  13. An airfoil placed in a super-cooled wind tunnel, coated with these nanos, and misted with water, shedding ice would convince me.
    Otherwise, call me skeptical. 🙂

  14. Can I get this stuff on the inner fenders of my car so I quite dragging all this snow sludge into my garage all winter?

  15. Cost and durability have yet to be shown, but promising. A friction reducing film for sailboats, “riblets”, worked so well that the IOC banned it from Olympic competition.
    If it a) really works and b) could be applied as a film to existing surfaces, companies like 3M would gobble it up.
    Good Science for a change.

  16. What could possibly go wrong?
    From: PaulH on November 14, 2010 at 1:21 pm:

    Pretty cool stuff, but I don’t think I like the idea of friction-free highways. That’s what they’re trying to prevent, right? 😉

    I read years ago they could easily make tires that would last 100,000 miles or more. Except they’d be so hard the braking distances would be several times longer.
    I’ve been driving more than long enough to appreciate having all the traction I can get. Sometimes I have needed all of it!

  17. jack morrow, ” … maybe it will cut down on the pre-takeoff deicing procedures that really slow down traffic at major airports.”
    There are two types of aircraft ice (and snow) contamination. First is precipitation that freezes (freezing rain) accumulates (snow) or forms (frost) on surfaces while the aircraft is on the ground. This can kill lift and requires pre-takeoff deicing procedures. For the material under discussion to work against this type of contamination it would have to be applied to most surfaces of the aircraft. It would not help with snow or frost (the most common causes of pre-takeoff de-icing).
    The second is ice build-up (freezing rain) on leading edges, windshields, radomes etc in flight. This type of contamination can happen very quickly, deform aerodynamic surfaces and add weight to the aircraft converting it from an aerodynamic wonder into a powered rock. Current solutions include avoidance, inflatable boots, “weeping wing” (de-ice fluid is forced out of the leading edges through millions of tiny holes) and heated surfaces. None are free. All add weight.
    NASA Glenn Research is studying this using an icing wind tunnel and a DHC-6 Twin Otter in the lee of the Great Lakes — where winters produce plenty of ice.

  18. Am I the only one who’s looking at these microscopic nano-engineered surfaces, and thinking all those tiny “pits” will get filled up with microscopic dust particles, they will prove highly resistant to cleaning, even scrubbing won’t work?
    They will fill up so far, stop shedding water as effectively, they can only be cleaned to where they shed off the liquid cleaning solutions. Once deployed, effectiveness will decline to a level they will stubbornly stay at, becoming less effective as the tiny structures are worn away. Scrubbing won’t work, bristles can’t get into the pits, and scrubbing will wear away the tiny structures quicker.
    Anyone else thinking that’s possible?

  19. re post by:

    B-52 says:
    November 14, 2010 at 2:28 pm
    “…could lead to a new way to keep airplane wings, buildings, powerlines, and even ENTIRE HIGHWAYS free of ice during the worst winter weather.”
    Say…
    “The concept of FRICTION-FREE surfaces that deflect supercooled water droplets…”
    …what?

    I may turn out wrong here, but suspect that ‘friction free’ on the micro-scale of water droplets doesn’t necessarily mean friction free or anything like that on the macro-scale of car tires to highway surface…. also suspect, however, that finding a way to incorporate it at a reasonable price that is also durable enough to hold up to the beating a road surface takes may be quite another issue. Would be nice tho!
    Regardless, very cool article and information! Good science at work.

  20. To those of you who think icing is a problem only for flight in Alaska, you are sorely mistaken. Icing is a regular problem even in California in the wintertime, and I recall one freak day in early August near Watt’s place that had some IFR aircraft as low as 11000′ needing lower altitudes to get out of it.
    A new Cirrus aircraft with deice capability had a horrible crash a few years ago when its pilot decided to brave a winter Pineapple Express storm to fly from Reno to Napa. Planes plummet when loaded with ice; in that flight, deploying the parachute was not the answer as it broke the airplane in two. Even jet transports don’t have perfect deice capability, but what they do have is the power to get out of it before it becomes a problem
    I live a few miles southeast of Chico, and in the winter I often can’t fly under instruments to land at my local airport because of icing.
    *IF* (and this is a big *if*) this results in practical anti-ice products for private or commercial aircraft, it will be a very big deal.

  21. Gary P says:
    Can I get this stuff on the inner fenders of my car so I quite dragging all this snow sludge into my garage all winter?

    I like the way you think!

  22. Scientific discovery the way it should be! And this technology could be in major demand in the coming years…..
    Chris
    Norfolk, VA, USA

  23. kadaka (KD Knoebel) says:
    November 14, 2010 at 4:52 pm
    “Am I the only one who’s looking at these microscopic nano-engineered surfaces, and thinking all those tiny “pits” will get filled up with microscopic dust particles, they will prove highly resistant to cleaning, even scrubbing won’t work?
    They will fill up so far, stop shedding water as effectively, they can only be cleaned to where they shed off the liquid cleaning solutions. Once deployed, effectiveness will decline to a level they will stubbornly stay at, becoming less effective as the tiny structures are worn away. Scrubbing won’t work, bristles can’t get into the pits, and scrubbing will wear away the tiny structures quicker.
    Anyone else thinking that’s possible?”
    At the car forums there are complaints about the nano car paint coatings losing their
    properties after a period of about 9 months.
    The shark skin foil developed by 3M that was going to reduce drag from air foils and fuselages had a similar problem of “dirtying up”.
    Anyhow, they are testing the new product and we will see what the result will be.

  24. Hydrophobic Coating
    Vellox Kit – TIN of 450ml 11,78EUR
    Vellox Hydrophobic Coating was developed in 1983 by Vellox Corporation of Massachusetts USA, as a coating for Radomes for use by the U.S. Military. Since that time the product has been accepted world wide for use on Radar Dishes and Radomes, for Military and Civil Communication Coating.
    Problems with Your Satellite Dish and the weather?
    No picture if it rains or snows?
    Best picture with Vellox.
    Water and snow pearling from your dish like on a hot cooking plate.
    http://www.wieser-electronic.de/catalog/product_info.php?products_id=64545&language=en

  25. I have about 4500 hours of Instrument time. about 1/3 is flight training, (Instructor
    time mainly) The rest Air Taxi, Commuter, and Freight/Mail. A lot of that over the
    West Coast of the US, and some in Alaska. Worst airframe icing is, surprisingly not
    Alaska, but the Cascades-that includes northern CA. I fell into Chico, too, one night on
    a Freight run in a 402 Cessna. Worked for Northstar out of Redding for a while.
    Picked up a load of rime at 12,000 ft. and had a heck of a time getting down until I could clear traffic and the Sierras.-This was out of Reno. Flew a lot out of Sea-Tac
    -the key was getting Altitude westbound over the Sound, then east after getting over most of the upslope icing that is common as a NorPac cold front blasts over the mountains. Another form of Icing that is common-Freezing rain, Portland/Troutdale
    The Columbia basin in Washington-very common back n the 60’s and 70’s. BTW
    I predict that is problem-freezing rain is going to be a big problem with wind
    turbines…
    I wish them well in this process, there has been many many efforts at figihting
    icing in aviation, this appears to be a breakthrough..

  26. Hang on… scientists doing actual research by figuring out what they don’t know, takinf high-speed photographs of the event in question and working from there?
    That’s not science. Science is building a computer model and ignoring messy stuff such as real world data.
    I don’t know what this methodology is, but it would sure be cool if it caught on!

  27. The ice on the plane in the picture is rime, accumulated from butting into supercooled water droplets. The movie shows warm water (+20C) hitting a cold surface. Apples and oranges. The question is, will supercooled water bounce off a surface before it has time to freeze?

  28. Strangely one of the more important areas to stop icing is the propeller blades. There have been several crashes where the propeller blades iced up and ‘stalled’ leaving the iced up aircraft with reduced lift from its wings and no, or worse, asymmetric thrust .

  29. “Similarly, salt on roads can lead to corrosion …”
    Toyota might be interested in this technology after that rusting frame problem they had on all those Tacoma pickups.

  30. To repeat a plug I did on an earlier topic and in the interest of focussing people’s minds on Cancun, I’ll plug it again. A link I think worth watching through the week.
    I may just be me but there seems to be a reporting blackout on the upcoming Cancun climate conference. The only site I can find addressing this void seems to be
    http://ourmaninsichuan.wordpress.com/
    which is running a Cancun week of blogs.
    Pointman

  31. According to the photograph caption the “… rubber boot had been employed prior to landing”. Times must be pretty tough for rubber boots these days – especially after landing!

  32. Pneumatic rubber boots have been around since the 1930’s Douglas’ DC-2,then 3’s
    brought them into wide spread use, developed by Goodyear, this concept is still quite common. Rime ice isn’t as bad as clear with boots, as there a point where you have to make a decision with clear- hit the boots, and take the nice, clean aerodynamic but heavy. shape pop the leading edge boots, and get a nice,sharp spoiler, this has happened to me. Rime is rougher on propellers and air intakes, Props are usually heated, as are windshields. Modern Airliners, including turboprops, can have “Hot wings” heated by jet bleed air, or as my old 1950’s vintage Douglas Airliners I flew as Airtanker(Retardant) aircraft they actually had gas fired wing heat. This is still around some, but I can’t be specific. Propeller heat is usually electric,btw.
    One Technology that I was around some was Alcohol for both wings and props.
    I knew a Hawker Siddley 700 business jet driver who had pour (sob) a liquor
    cabinet (blubber) full of single malt (WAAAH!) scotch, during a rough trip into
    Billings Montana….

  33. Believe me, this will make the Warmists unhappy. Some silly argument about water vapor will arise. One thing that Warmists cannot stand is real science.

  34. This is great stuff. Nature already has design solutions for many engineering challenges, and the effort to reverse engineer nature’s designs is an exploding field that has, and will continue, to yield numerous exciting discoveries. Observations, engineering (with real math and materials), testing, and then real-world applications. Applied science at its best — quite a contrast to much of what passes under the name of “science.”

  35. Back in olden times, the Boeing 727’s had squirt-on rain repellent called ‘Rain-Boe’ that you dispensed only when the windscreen was wet because it otherwise dried to an impermeable haze they had buff out with polishing compound. Worked great, but it apparently caused penguins to get skin cancer from ozone holes, so they banned it. Messed up a few white shirts afterward leaning out the cockpit window to rub Rain-X on the windscreen (on the ground).
    Boeing 777’s have hydrophobic windscreens, which we were forbidden to Rain-X. They sort of worked, but not as well as Rain-X, and nowhere close to Rain-Boe.
    Triple-7 also had ice sensors and automatic bleed air deicing. Deluxe compared to my light twin days trying to gauge if I had thick enough ice on the rubber boots so it would break off cleanly, rather than what happened to the plane in the picture, where he cycled the boots too soon and ended up with ice strips adhering to the boots.
    For the past several years I couldn’t find Rain-X at Wal-Mart. I guessed the EPA got to it as they do to all good sensible things, but recently Rain-X has reappeared. I stocked up, and have a cache sitting next to my cache of tungsten light bulbs.

  36. Back in 1962 when I started to train as a Royal Air Force navigator, way before GPS, we were told how dangerous ice buildup on an airframe was and why it formed. Water droplets at height can be super-cooled, ie. liquid below normal freezing point, and any disturbance will cause instant freezing. A cold airframe hitting these droplets causes instant ice to form on the leading edges of all sections. The normal anti-icing systems were usually enough to cope but not always. The sound of large ice chunks breaking off the propellers and hitting the airframe was sometimes a worry.
    Ice buildup causes lack of lift and eventually a crash if the icing problem is not resolved.

  37. Owls are especially silent as they glide in on their prey due to microstructures on their wings. I wonder if a new nano material will make planes and boats (and subs?) more stealthy and slip through air/water with less drag?

  38. Just don’t let the Wind turbine manufacturers know about this!
    Still, why not? They won’t use it as they are now taken up with the manufacture of ‘stealth’ turbines. As turbines upset radar, some bright spark came up with this idea. Production is now up and running – official!
    Just one slight problem that does not seem to have occurred to them. If they are invisible to radar then aircraft will not see them either, nor will shipping see them when negotiating around these wind farms out at sea in a fog!
    Wasn’t it the Ravenous Bugbladder Beast of Traal that was so stupid that it assumed that if you couldn’t see it, then it couldn’t see you?

  39. “The finding, reported online in ACS Nano on November 9th, could lead to a new way to keep airplane wings…”
    The word “could” in the above sentence is the smoking gun. I’m a materials engineer (and current PhD candidate) with over 20 years in the business. I don’t know how many times I’ve seen articles on nanotechnology making similar claims yet most fail to pan out, at least in the short-term. My own belief is that these press releases are designed to promote the research with the sole intent of ensuring continued funding.
    Maybe there’s a “Nanogate” waiting in the wings…

  40. Well actually there is nothing new about this idea or technology; BUT I would agree that anti-icing is a new application that could be of great value.
    For $100 you can buy a nice brand new 3-M (Scientific Anglers) fly fishing line, which has a nano-structured surface that makes it extremely hydrophobic. Their rade name for it is the Sharkskin Line.
    3-M has used this technology for eons. One of their most famous uses of it was its use by Dennis Connor, on his America’s Cup Yacht in the 1987 America’s Cup Challenger series in Fremantle Australia. The 12 Metre formula that was then being used allowed a designer to exchange hull waterline length for maximum sail area. A longer hull had a higher hull speed; but then you would have less sails to power it. That wouldn’t matter if the wind speeds were high. On the other hand with low wind swpeeds that would favor a shorter hull and a bunch of sail.
    The Wind history (obligatory climate content) showed that by the time the actual AC races started; the “Fremantle Doctor” would show up, and wind speeds would be high; but they were low when the Challenger preliminary races started. Connor opted for the longest hull length for his “Stars and Stripes” Yacht. That made him somewhat slow in the preliminaries, and he nearly didn’t make it into the final rounds. 3-M supplied him with some of their sharkskin tape, to coat the hull with, and that gave him enough extra speed to eventually defeat the New Zealand team and win the Challenger series. Then in the AC races themselves, his boat was clearly superior in speed with the high winds, and he easily beat the Autralian Defenders. The Sharkskin was then banned from use in the cup races.
    But sailors know to sand their hulls with the right grade of sandpaper to roughen the surface to the correct pit size.
    The basic functioning principle is the surface tension and internal pressure of bubbles.
    A water droplet or an air bubble in water must have an excess internal pressure over the outside ambient pressure; and the amount of that internal pressure excess is given by 2T/r, where T is thew surface Tension in Newtons per metre, and r is the radius of the droplet or bubble in metres. So the smaller the bubble, the higher the internal pressure.
    If you make pits on the surface that are roughly hemispherical in shape (exact shape doesn’t matter), then water has to form a surface of shorter radius than the pits, in order to get down into the pit and actually wet the surface. Instead the bubble sits up on the rim with a larger radius, so it is like a water strider sitting on the surface.
    With the sharkskin fly line, 3-M is able to create a higher floating line, since the pits literally lift the line off the water surface, which simply refuses to curve into a smallenough radius to wet the line surface at the bottom of the pits. The internal excess pressure is literally lifting the line off the surface, so lowering its apparent density.
    So you put such a pitted surface on a plane wing, and water droplets driven onto the surface at some velocity are going to be repelled from the surface by those pits.
    The sharkskin fly line is quite amazing; when you pick it up off the water surface into the air, it literally rains underneath the line, as water streams of fthe surface. It also makes an annoying buzz, going through the guides on the rod, and it peels the skin off your stripping fingers; but it sure does float better than any other fly line. The patter they use is basically a diamond grid; and they literally have to emboss it onto the circumference of the lien from end to end, one line at a time; there is no bulk process for putting it on the plastic coating; which is why you pay $100 for a line that normally would be $65.

  41. “”””” Dave says:
    November 15, 2010 at 10:09 am
    “The finding, reported online in ACS Nano on November 9th, could lead to a new way to keep airplane wings…”
    The word “could” in the above sentence is the smoking gun. I’m a materials engineer (and current PhD candidate) with over 20 years in the business. “””””
    Dave; may I suggest you try to get a PhD in Ice Cream Making instead of Materials Engineering.
    If you are doing a PhD in ME and you aren’t familiar with the internal excess pressure of bubbles; then you need a change of career; or at least of your PhD advisor. Don’t forget that with soap bubbles the internal pressure is 4T/r because there are two surfaces to a soap film. It should be a trivial derivation for you to prove Dave; I would hint that the principle of virtual work leads to a very easy derivation.

  42. George,
    First of all, I said nothing about doing my dissertation in nanotechnology. Materials engineering is a very broad field of which nano is just a very small piece (pun intended). But I’ve been watching the area for a long time and have seen time and time again where such discovery announcements have been made only to never again see the light of day. As I intimated in my original post, the same PR tactics used in AGW research exists in other fields.
    Care to go get an ice cream cone?

  43. Trees Infused With Glowing Nanoparticles Could Replace Streetlights
    Taiwanese researchers have come up with the elegant idea of replacing streetlights with trees, by implanting their leaves with gold nanoparticles. This causes the leaves to give off a red glow, lighting the road for passersby without the need for electric power. This ingenious triple threat of an idea could simultaneously reduce carbon emissions, cut electricity costs and reduce light pollution, without sacrificing the safety that streetlights bring.
    http://www.popsci.com/technology/article/2010-11/trees-could-one-day-serve-streetlights-thanks-gold-nanoparticles

  44. “”” Dave says:
    November 15, 2010 at 12:00 pm
    George,
    First of all, I said nothing about doing my dissertation in nanotechnology. Materials engineering is a very broad field of which nano is just a very small piece (pun intended). But I’ve been watching the area for a long time and have seen time and time again where such discovery announcements have been made only to never again see the light of day. As I intimated in my original post, the same PR tactics used in AGW research exists in other fields.
    Care to go get an ice cream cone? “””””
    Well Dave, I do hope you didn’t take any offense; because none was intended, and I hoped you would see the tongue in cheek; well Ic an be a cheeky guy. And I do like your ice cream cone suggestion; I’m actually out to lunch as soon as I post this.. No I didn’t imply you were working in nano-technology; and that certainly has many sides to it.
    But the 3-M sharksin fly line works like a dream; but there’s as many people hate it as love it.
    In the event that you aren’t familiar with the excess pressure in bubbles due to surface tension; I could rattle off the derivation here in a few minutes; but only after I get back from getting my ice cream cone lunch.
    George
    PS in the virtual work approach you calculate the work done by the excess pressure during a small increment in radius; and you equate that to the work done by the increase in surface area agaisnt the surface tension; QED.

  45. Well I might as well do it for all those who maybe don’t quite understand the idea; since it actually is quite important in climate and may pay an important role in cloud formation.
    Surface tension, T is a constant force in Newtons per metre that acts in a liquid surface trying to pull the surface into a minimum area lowest energy state. It is easiest to demonstrate with the “parallel wire” approach where you have a wire bent around to form an end loop and two parallel wired spaced (w) apart. Then you have a sliding cross wire such as a needle lying across the wires to form a closed area (A). So you dip this into a soapy water solution to form a film covering the area.
    The surface tension will try to pull the needle down to the loop to reduce the film area, and the pulling force will be 2 T.w, Newtons where the 2 comes from the fact that the soap film has two surfaces pulling on the needle. Unlike a rubber balloon skin which would have a force proportional to the stretch; the surface tension force is absolutely constant and independent of the film area. Now it is of course highly dependent on conditions and Temperature, which will change the value of the surface tension.
    So if you let the film pull the needle a distance (l), then the area will be reduced by l.w, and the work done will be T.w.l or simply T times the change in surface area; well I forgot the factor of 2 so it is 2T x delta (A). Well I fooled myself here because since the film has two sides, the actual change in area is 2 w.l, so the work done by a surface is indeed T delta (A).
    So now we have our water droplet of radius (r), so it has a surface area of 4pi.r^2. If we let the droplet grow to r +dr then the surface area becomes 4pi(r^2 +2r.dr) and we ignore the miniscule (dr)^2.
    So the increase in surface area is 8pi.r.dr. The work done agaisnt the surface tension will then be (8pi.r.dr).T
    Now the surface tension pulled the droplet into a minimum area sphere, and was only stopped from crushing it to nothing by the internal pressure (p) that results from the surface tension . This pressure acts over the entire surface area of 4pi.r^2 to give a total outward force 4pi.R^2.p, and in moving the surface by (dr) the internal pressure would do work 4pi.r^2.p.dr
    So we equate the two measures of the (virtual) work done; 4pi.r^2.p.dr = 8pi.r.dr.T
    Some third grade algebra gives:- r.p = 2.T or: p =2T/r
    So this holds true for a water droplet, or for an air bubble (or water vapor bubble) inside a water that may be in the process of boiling. The water vapor pressure would have to be equal to the ambient pressure in the water (in order to boil) PLUS the excess pressure of 2T/r.
    So we have the odd problem that the vapor bubble has to start off at zero radius; but that requires an infinite excess internal pressure; so the Temperature must rise above the true boiling point, trying to generate enougfh vapor pressure for a bubble to exist.
    Well dust and microbes, and even cosmetic rays can come along and form nucleation sited having a non zero radius that allows the vapor bubble to form at less than infinite temperature. Well the lesson from this; is that you DO NOT want to NUKE a cup of very clean water in your microwave. With the very uniform heating and no nucleation sites; the water will superheat; and if you bring it out and a dust particle falls into it; the whole damn thing can explode in your face.
    So put the coffe grinds in before you nuke the water or else. That’s why the kettle will pop and bump on the stove as it tries to boil internal to the liquid; and having to generate an overpressure to sustain bubbles.
    Now I haven’t quite figured out the way in which this surface tension excess pressure mechanism affects the formation of rain drops; but I’m sure that it does; and of course The Cosmic ray theory of cloud formation is related to this. As is the role of aerosols in the formation of clouds.
    And I know that it works to get fly lines to shed water; and maybe ice too. Some fly fisherfolk I know are actually dumb enough to fish in icing conditions, where their guides get filled up with ice, and the ice sticks to the fly line.
    An interesting anecdote; I happened to be present at the Fishing Tackle trade show held in Denver; a couple of years back, when 3-M, Scientific Anglers introduced their “Sharkskin” line, and had a big booth demonstration of the thing, and they were handing out samples of the material, that went from smooth to rough so you could feel the surface.
    I happened to walk up to their booth just as one of the technical experts from their biggest fly line competitor was walking away. The competitor (another very fine fly line manufacturer) was giving a private seminar to all of its reps and sales people lauding the virtues of their newest super slick and smooth fly line technology, that they were introducing at the same show; and evidently the chap had been at the 3-M booth telling them they were all wet (pun intended). So they handed me the Sharkskin sample; and a very famous fishing figure and fly casting expert; who however has only a high school education; asked me; say George, how does this thing work ? Well I could feel the rough surface but I hadn’t even looked at the photomicrographs of the actual surface showing the diamond embossing; that they had on a computer in another part of the booth. So I took over the flip pad and marker pen, and launched into basically the above explanation of why this should work, according to the laws of Physics. Well it was faster to do on the flip chart than to write the above.
    The fly guru said wow; even I can understand that. Then the guy next to him, with a 3-M badge piped up. He said I just spent an hour here trying to explain this to the guy from (XYZ-company) who just left here. Why don’t you stay here and explain it, because I like your explanation a lot better than mine. Turns out he was the chap who invented the stuff. His explanation involved all sorts of contact angles and other complexities (all of which was correct).
    The lab R&D people at 3-M incude a lot of very high power researchers; they truly are a high tech company. I always pull the leg of the fly line people; by asking them how they ever got permission to put out a 3-M product that doesn’t have a sticky gum on the back of it.
    Applying this to the de-icing problem is quite interesting, and I will be fascinated to see what comes of it.
    But Dave’s caution may be appropriate; it might be a more theoretical solution that is hard to implement in practice. It would be nice thoguh because the leading edge rubber boot de-icer is a bit of a complex and somewhat Rube-Goldberg solution.

  46. I wonder if they looked at the skin friction with these materials, when used as aircraft skin. at 600mph, any increase in friction coefficient will stop this dead in it’s tracks.

  47. “Well dust and microbes, and even cosmetic rays can come along…”
    What do Mary Kay and Maybelline have to do with this? 😉
    Looks to me like a good coat of wax would totally bollix up any of those nano structured surfaces.
    From my own personal experience WRT ice, a smoothly rough ice surface is far easier to slip and fall on than a perfectly flat ice surface. When formed under the right conditions, ice can have an evenly bumpy surface that’s all smooth. Walking on it is like trying to walk on a concrete floor covered with oiled bearing balls. Without active surface deformation traction aids (metal spikes) the smooth ice lumps allow your shoes to easily slide in any direction.
    In contrast, a dead flat ice surface provides maximum contact area with shoe soles, higher than any typical dry and solid surface. (A dry concrete surface that’s not polished has billions of little pits and lumps in the area covered by an average shoe sole. The roughness and lack of lubrication provides the traction that keeps your feet under you.) Of course pressure melting will still make the flat ice slick but with higher sticktion than the smooth/bumpy ice.
    Now… take the smooth/bumpy ice texture down to nano scale so the lumps and the spaces between them meet the criteria for all that math posted higher up. 🙂 My bet is water will shed off because it won’t be able to fully wet the surface yet where the entire surface is smooth with no sharp edges, there won’t be anywhere for really fine dust to catch and slapping on a coat of wax or Rain-X (followed by appropriate buffing off of excess) shouldn’t significantly degrade the water shedding, if it does at all.
    Mail the big $ check to…

  48. Greg E.;
    Ever heard of “curling”, the sport? Getting just the right “pebble” on the ice is key to proper slide and curl of the rocks. YCLIU
    George E.;
    About 3-M – makers of Scotch brand. I claim copyright on the following advert slogan which I’m going to license to them: “Tape it and stick it!”
    You read it here first. 😉

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