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Semipermeable membrane for gases?

  1. Mar 5, 2009 #1
    Is there any kind of semipermeable membrane which would diffuse gas but wouldn't let liquid to pass. If yes what would that be?

    Thanks, Vladimir.
  2. jcsd
  3. Mar 5, 2009 #2


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    For any liquid and any gas? Probably not.

    For a specific pair? Perhaps.
  4. Mar 6, 2009 #3


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    What about Goretex?
  5. Mar 6, 2009 #4
    Yes, somebody had also suggested that to me.

    Also it can be for specific gas/liquid (which ever).

    But what about pressure.. would gas diffuse if on another side is liquid with slightly higher pressure? (like water does)
  6. Mar 6, 2009 #5


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    Absolutely. Everything is permeable in everything else. What permeation rates are you wanting to see?

    Mass transport always proceeds from regions of high chemical potential for a species to regions of low chemical potential; it ceases when activities of all species are equal on both sides of the "membrane." Differences in permeation rates for various species allow the opportunity to run "horse races" and achieve separations of mixtures/solutions; run the the race long enough and every horse crosses the finish line.

    How long a race (how thick a membrane), and among what species (cheetahs, snails) are you wanting to run?

    Gas/membrane pairs? O2/Cu, He/SiO2, H2/Pd(any metal, really), and the gases are all soluble in any liquid you care to select.
  7. Mar 6, 2009 #6


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    Well what I was trying to say that you can't possibly (in my mind) create something that's essentially permeable to any and every liquid and essentially impermeable to every gas. Or vice versa.

    After all, 'gas' and 'liquid' are phases, which isn't a property that's very noticeable on the level of individual molecules. It's not like a single molecule of H2 in water is going to hold up a sign saying "Hi, I'm a gas!"
  8. Mar 7, 2009 #7
    permeation rate - the higher the better

    However, I want to try this at home, so it shoud be simple.
    The gas really doesn't matter as long as its not He or H. It would be good that its colored gas. My first thought was Cl2 made at home from electrolysis of NaCl dissolved in H2O. All in all I want to be able to make/find gas and membrabe at home and to test it. It would be good to have higher permeation rate , but nothing fancy. Any suggestions?
  9. Mar 9, 2009 #8


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    Are you insane?
    You do not, I repeat not want to mess around with chlorine gas at home. That stuff is extremely dangerous, toxic and corrosive. You do not mess around with chlorine under a fume hood even, if you can avoid it. (and even then you'd still pass any excess gas through some neutralizing solution)

    The other halide gases aren't very nice either. I'd suggest forgetting about using colored gases. There aren't very many of them, especially once you rule out the dangerous ones.
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