Wednesday, December 10, 2008

What if... #10

What if water had a vanishingly small surface tension?

This post is part of the 2008 advent series "What if..."


  1. -There would have been no water skiing

    -Falling from a great height into water might actually save your life

    -Ducks could not swim for their feathers would quickly saturate with water

    -No stone skipping

    -Worst of all no one could blow a bubble

  2. I don't think life as we know it could exist without it.

  3. Hi Rae Ann,

    "I don't think life as we know it could exist without it."

    This is true and now you've burst my bubble for there would be no one to blow one to begin with:-)

  4. The opposite is also quite interesting: It would make drinking quite hard as is discussed here:

    esp. section 2

  5. However, one can reduce water's ST by adding chemicals, hence there's something that makes it easier for firefighters to spray water:

    Scotty FIREFIGHTER has developed products with that in mind. The forest industry has long understood the benefits of foam as an extinguishing agent. Basically, foam concentrates are specifically formulated to make water more efficient by reducing surface tension, allowing the water to spread out and create a protective blanket, knocking down the fire more quickly and protecting the surrounding areas.

  6. Rae Ann's thought was my first one too. Life, if it existed, would be very different.

  7. No capillary action - no trees, no absorbent soils. No surfaces and apertures kept dry by capillary exclusion. No running along the surf line at a beach, no water striders, no double-edged razor blade floating on water demo, no dilatant fluid cornstarch-water demo. No cell membranes. Greaseball Earth.

    Press together two clean microscope slides beneath the surface of deaerated distilled water (72.8 mN/m surface tension). Try to separate them. Does the demo work in hexane (18.43 mN/m) or low viscosity silicone oil (19 mN/m)? Perfluorohexane is 11.91 mN/m., 6M aqueous NaCl is 82.55 nM/m.

  8. Ooh, cool, smart people are agreeing with me! :-)

    Phil, sorry about the burst/nonexistent bubble.

    I don't really know enough about the intricacies of these things, but would water have the same surface tension on a different planet with different gravity, etc. values?

  9. I'm not sure, but probably one cannot change the surface tension without altering a lot of other thermodynamical properties: vapour pressure, hence phase boundaries, transition temperatures, and so on. The stuff could be very different from water as we know it.

    Cheers, Stefan

  10. Would trees still be possible?

    (There's been a lot of debate on how water gets up tall trees, which I haven't followed carefully. So, I don't really know.)

  11. Well, making a splash dive on your belly would still hurt.. wouldnt it? considering inertia of the water you need to displace before your body is fully submerged.



  12. Hi Rae Ann,

    Ooh, cool, smart people are agreeing with me! :-)

    I think it’s been proven in this case who the smart one truly is:-)

    “I don't really know enough about the intricacies of these things, but would water have the same surface tension on a different planet with different gravity, etc. values?”

    As for your question, surface tension is produced by nature just acting to confine the greatest amount of volume within the least amount of surface area in relation to the applicable forces responsible. The main force involved here would be the electromagnetic one attracting all the molecules to each other and would be consistent for the most part wherever it’s found (that’s if it where still a liquid). Gravity would play a role in a pond where it’s confined yet in a bubble where it’s falling (free fall) this would add less to its effect. So the answer would be yes and no, with of course the electromagnetic force being the more consistent and dominant factor. This is just one of the many instances where the Lagrangian(least action) aspects of nature makes its presence felt.



  13. Hello,
    only two out of Phils 5 items is related
    to surface tension, i. e. the swimming of
    ducks and other birds, as well as the
    thermal insulation of seals or penguins
    in sea water.
    Blowing bubbles: this is more or less
    impossible with pure water, detergents
    lowering the surface tension down to
    values comparable to those of hydrocarbons
    are necessary.
    "Vanishingly small" surface tension for
    some liquid is impossible, maybe You think
    of liquid helium?
    Liquids at standard conditions need to
    have surface tension
    like fluorinated hydrocarbons at least,
    otherwise the would be too low intermolecular forces, hence there would be
    no liquid.
    The most dramatic of water having a
    reasoable low surface tension in my opinion
    was the difference in condensation process.
    i. e. cloud formation. Much rain would fall on sea already, the continents were much drier.
    Background is the internal pressure of small droplets, which retards the
    condensation of supersaturated air.

  14. `Georg,

    So you are saying that stone skipping or water skiing are not influenced (increased in effect) by surface tension? In regards to hitting the water I understand that any acceleration would have gteat effect yet for example in a clean dive as opposed to a belly flop there is a large initial resistance meet when encountering surface tension. As for bubbles I think it misleading to have anyone think that the presence of surface tension is not the main requirement in having them be possible as the detergent has more to do with increasing their stability (life span) and size then anything else. In the end I think the differences here are do largely to superficial tension:-)



  15. Hi Dr. John,

    “Would trees still be possible?”

    Yes, good question although I think the more recent findings would leave us thinking that without surface tension it would not be possible. Of course to deny it would require us to deny much more fundamental aspects of nature. It is interesting to note that with all the theorists contemplating a theory of everything it is still not clear how the tops of a Douglas fir tree get a drink :-)



  16. Hello Phil,
    yes indeed, water skiing and stone chipping
    is 99.9 % inertia at least. The tiny effects of
    ST (surface tension) can be neglected.
    On top of that, for evaluation of ST in
    such cases, You have to have a look on
    wetting behaviour (contact angle) as well.
    E. g. take mercury, like all liquid metals
    it has a ST even higer that the ST of water,
    but nevertheless it displays capillary depression.
    This means, the small forces of ST will lower
    the inertial forces when chipping stones, in case the stone is easily wetted.
    Lifetime of bubbles:
    very complex phenomen. The most stable bubbles
    are made from water, glycerol and
    2-Ethylhexylsulfosucccinate as a detergent.
    This detergent has an rather unique property:
    an extended "two phase region".
    This is an analogy in surface pressure
    to gases below critical point.
    In this region multiple layers of the
    dertergent occur, the ST is constant
    over surface. Rather likely this phenomen
    is related to the stability of those bubbles.
    The glycerol slows down vaporistion
    and makes more viscosity.
    The breaking of a soap film is a process
    which needs some activation (some pinhole)
    first. The rather thick dertergent layer
    makes a kind of protection against
    such "pins" (dirt) which cause the
    rupture (my personal reasoning)
    Drawing a film of pure water (eg on a
    ST-balance) is very much dependent on
    cleanliness of the water.
    Whether the low ST of the soap bubble
    films helps to form/stabilize soap
    bubbles, is a difficult question, because
    the best You achieve under lab conditions
    is seconds for stability of films from
    pure water. (This is reason, why ST-balances
    used to be spring balances, You did not have time to fiddle around with weights.)
    If one wanted to do a experimentum crucis
    on this question, one needed some way to
    lower ST of water without all the other
    side effects of a soup bubble receipt.
    The problem is somewhat of the nature
    of "wash me but don't wet me" :=)
    (translation of a german proverb; its
    the equivalent to keeping and eating the cake)

  17. Hello,
    some posts her say that trees depend on
    capillary forces to bring water to the
    top leafs.
    I'd like to know who set free this "rural" legend.
    For the time being and the honor of physicists,
    I take it for granted, this comes from a biologer. :=(
    Some reasons :
    cut a twig of some wine in springtime, or most impressive,
    cut a pumpkin from a green branch.
    If the flow was dependent on capillary,
    the juice would not flow out of such a
    wound, i. e. the upper end of a capillary tube inserted into water.
    Capillary forces are like suction from
    the top end of the tube.
    The maximum height You can lift water by suction
    is theoretically 10 meters, in practice only 7 meters.
    After 7 meters, the dissolved air and vapor pressure of water set a limit.
    So what about all the trees exceeding
    this 7 meters?
    The lift of the water in all plants is due to
    some pressure generated in the roots,
    an example of such a biological system
    is common to animals: kidneys.
    The "manometer" in everyones bladder is
    is rather convincing at times.

  18. You can eliminate the surface tension of water by shrinking the dipole moment of the O-H bond. A molecule with similar geometry and valence structure is SH2, but the S-H bonds have a much smaller dipole moment, because S is much less electronegative than O. So, just make O less electronegative, and voila. As water is very small, it has little surface area for van der Waals attraction due to London dispersion. You wind up with a gas at STP. Life needs to look for another solvent, I'm afraid.

  19. Thanks for the comments about trees, and the pointing out of H2S. Here are some phase diagrams for H2O and H2S - the vapour pressure curves can be seen in the upper right plots. Indeed, H2S boils at standard pressure at much lower temperatures than water - just above 200 K.

    Cheers, Stefan

  20. Hello
    Low Math, Meekly Ineracting said...
    and Stefan,
    thank you, but I meant that not in this way.
    To decide Phils question, whether low
    surface tension is reponsible for the soap
    bubbles or "only" stabilizing the bubbles,
    one needs water with low surface tension but
    all other things should be unchanged, which is of course impossible.

    The boiling point relations and some more between analog first and second period compounds is basic chemistry,
    think of ammonia-phosphin or hydrogen fluoride - hydrogen chloride.
    But Methane- Silane is "regular" afaIr,
    due to symmetry and lack of dipoles.
    Best regards

  21. The What if becomes a interesting reading on the Navier-Stokes and tension and lack thereof.


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