Remain dry underwater

Discussion in 'Chemistry' started by timojin, Aug 20, 2015.

  1. Secular Sanity Registered Senior Member

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    264
    Your kidding, right? Did you click on the first link? I mean, all we can really do is read their paper, right? That article contained the link. Jeez, you're a lazy one.

    http://scitation.aip.org/content/aip/journal/jap/117/3/10.1063/1.4905616

    "The researchers created the surfaces by zapping platinum, titanium and brass samples with extremely short femtosecond laser pulses that lasted on the order of a millionth of a billionth of a second. “During its short burst the peak power of the laser pulse is equivalent to that of the entire power grid of North America,” Guo said.

    These extra-powerful laser pulses produced microgrooves, on top of which densely populated, lumpy nanostructures were formed. The structures essentially alter the optical and wetting properties of the surfaces of the three metals, turning the normally shiny surfaces velvet black (very optically absorptive) and also making them water repellent."

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  3. Daecon Kiwi fruit Valued Senior Member

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    Are there hydrophobic versions of sufaces that repel other liquid chemicals, for example acids?
     
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  5. timojin Valued Senior Member

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    Most of strong acids are dissolved in water. I believe in order to be an acid , the parent compound have to donate a Hydrogen to a water molecule. to produce an Hydronium Ion .
    Take example Teflon, I would expect be hydrophobic to glacial acetic acid , and to sulfurous acid 100% SO4H2
     
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  7. exchemist Valued Senior Member

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    No, of course I read it. But why would this lumpy surface repel water molecules? There is no explanation. There is clearly some ingenious surface chemistry going on here and I'd like to understand what. Especially when their video says that they had previously used a similar laser treatment to produce exactly the opposite effect, viz. a surface that is highly attractive to water molecules.
     
  8. exchemist Valued Senior Member

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    6,477
    Acids are perhaps not a very good example since the whole business of acid/base reaction rather assumes aqueous chemistry. But there are certainly oleophobic surfaces for example. https://en.wikipedia.org/wiki/Lipophobicity
     
  9. Secular Sanity Registered Senior Member

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    You're just messing with me now, right? As a chemist, you don't understand the lotus effect?
     
    Last edited: Aug 22, 2015
  10. exchemist Valued Senior Member

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    6,477
    Read this: https://en.wikipedia.org/wiki/Lotus_effect

    The lotus effect depends on a surface coating that is itself hydrophobic (waxy), augmented by a surface structure composed of tiny, needle-like protrusions. The combination of the two leads to water drops being almost spherical on its surface, due to the angle of contact phenomenon.

    Metals, however, are not in themselves hydrophobic. Contact angles of water with metals are typically close to zero: https://en.wikipedia.org/wiki/Contact_angle

    So the lotus effect does not explain what is happening here. Also, I repeat, how do they also produce the opposite effect using a variant of the same technique?
     
  11. sideshowbob Sorry, wrong number. Valued Senior Member

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    2,961
    Yes, that's what I meant. Dry inside is more important than dry outside. On the other hand, the "stickiness" of water might be a problem for movement, so a hydrophobic surface would still be desirable for that reason.
     
  12. Secular Sanity Registered Senior Member

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    264
    If you click on "the lotus effect" in my paragraph, you’ll notice that it’s a link. I did read it. Did you?

    "In additional to chemical surface treatments, which can be removed over time, metals have been sculpted with femtosecond pulse lasers to produce the lotus effect. The materials are uniformly black at any angle, which combined with the self-cleaning properties might produce very low maintenance solar thermal energy collectors, while the high durability of the metals could be used for self-cleaning latrines to reduce disease transmission."

    They obviously altered the contact angle, and in their paper they said that metals are intrinsically hydrophilic; immediately after femtosecond laser surface structuring, they first become more hydrophilic, but the exposure to air turns the metals superhydrophobic. This transition is explained by chemical interaction between the surface and the ambient CO2, resulting in an accumulation of carbon and its compounds on the laser-treated surface.

    "We believe that the laser-induced surface nanostructures also play an important role in enhancing this chemical interaction due to nanochemical effects."

    Did you read their paper?
     
    Last edited: Aug 22, 2015
  13. exchemist Valued Senior Member

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    6,477
    Aha so that's it. Some sort of accumulation of carbon compounds, due to reaction between the newly exposed metal surface and ambient CO2. Good, thanks for that. And no I had not read the Japanese paper, as you seemed to know all about it and I had hoped you might tell me what you had found out.
     
  14. Secular Sanity Registered Senior Member

    Messages:
    264
    Japanese paper? You mean JAP as in the "Journal of Applied Physics"?

    http://scitation.aip.org/content/aip/journal/jap/117/3/10.1063/1.4905616

    Mm, hmm...like I said earlier...lazy.

    You’re welcome.

    Enjoy your day!
     
  15. exchemist Valued Senior Member

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  16. kilao Registered Member

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    I always thought it was a physical phenomenon... Sorry...
     
  17. timojin Valued Senior Member

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    Be it physical or chemical iot is science . Water is chemical surface roughness is physical they interact
     
  18. timojin Valued Senior Member

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    http://www.ecnmag.com/news/2015/12/...?et_cid=4994493&et_rid=439217393&location=top
    "In the lotus leaf, these are due to papillae within the epidermis and epicuticular waxes on top," he said. "In our material, there is a microstructure created by the agglomeration of alumina nanoparticles mimicking the papillae and the hyperbranched organic moieties simulating the effect of the epicuticular waxes."

    Fabrication and testing of what the researchers call a branched hydrocarbon low-surface energy material (LSEM) were carried out by lead author Shirin Alexander, a research officer at the Energy Safety Research Institute at the Swansea University Bay Campus.

    There, Alexander coated easily synthesized aluminum oxide nanoparticles with modified carboxylic acids that feature highly branched hydrocarbon chains. These spiky chains are the first line of defense against water, making the surface rough. This roughness, a characteristic of hydrophobic materials, traps a layer of air and minimizes contact between the surface and water droplets, which allows them to slide off.

    To be superhydrophobic, a material has to have a water contact angle larger than 150 degrees. Contact angle is the angle at which the surface of the water meets the surface of the material. The greater the beading, the higher the angle. An angle of 0 degrees is basically a puddle, while a maximum angle of 180 degrees defines a sphere just touching the surface.

    The Barron team's LSEM, with an observed angle of about 155 degrees, is essentially equivalent to the best fluorocarbon-based superhydrophobic coatings, Barron said. Even with varied coating techniques and curing temperatures, the material retained its qualities, the researchers reported.

    Potential applications include friction-reducing coatings for marine applications where there is international agreement in trying to keep water safe from such potentially dangerous additives as fluorocarbons, Barron said. "The textured surfaces of other superhydrophobic coatings are often damaged and thus reduce the hydrophobic nature," he said. "Our material has a more random hierarchical structure that can sustain damage and maintain its effects."

    He said the team is working to improve the material's adhesion to various substrates, as well as looking at large-scale application to surfaces.
     
  19. Secular Sanity Registered Senior Member

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    By means of microscopic observation and astronomical projection the lotus flower can become the foundation for an entire theory of the universe and an agent whereby we may perceive the Truth.~Yukio Mishima
     

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