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Researchers have devised a way to make liquid flow against gravity through capillary action by etching tiny channels into the surface of a metal plate with a high-intensity laser. Even when the plate is vertical (see video below), liquid climbs up through the channels at a speed that the researchers say is unprecedented.

Such passive transport of fluids could find use in the field of microfluidics, for instance, in which tiny amounts of liquid are shepherded around for sensing or lab-on-a-chip applications.

In a paper published online this week in Applied Physics Letters, Anatoliy Vorobyev and Chunlei Guo of the University of Rochester's Institute of Optics describe using 65-femtosecond laser pulses to etch the parallel microchannels into platinum plates. (Each laser blast is vanishingly short—there are nearly as many 65-femtosecond intervals in a second as there are seconds in a half-million years.)

The researchers found that capillary action and evaporation drew liquid methanol, also known as wood alcohol, through the channels at a rapid clip—one centimeter (0.4 inch) per second when the plate was vertical, and even faster on horizontal or slanted plates.

What is more, the volumes wicked upward were not trivial. In a separate setup, Vorobyev and Guo laser-treated a strip of platinum foil shaped like a "J," then submerged the long end into a reservoir of methanol. Ten minutes later a large drop of methanol had pooled at the short end of the "J," some 10 millimeters above the surface of the reservoir.

Photo of Guo in front of a femtosecond laser: Richard Baker, University of Rochester; Video courtesy of the University of Rochester

5 Comments

1. 1. fyngyrz 05:39 PM 6/3/09

   So... liquid crawls uphill on its own... lots of these amount to a steady flow of liquid... same liquid runs downhill over a water wheel, which creates energy... aren't Maxwell's demons getting angry about this?
   

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2. 2. NatureTM in reply to fyngyrz 05:43 PM 6/3/09

   Perpetual motion was my first thought. I don't believe it though. Can someone explain?

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3. 3. bfm 05:58 PM 6/3/09

   No perpetual motion here, just capillary action. The wicking process here is exactly the same when you clean up your kitchen with a paper towel. They just figured out how to do it with metal, which is a first. As far as Maxwell's demon, perpetual motion would require that the capillary bonds be released. That would require release energy, not found in this system

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4. 4. EvDubb 07:33 PM 6/3/09

   "Any technology distinguishable from magic is insufficiently advanced" making water run up seems pretty magical
   

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5. 5. fyngyrz 08:40 PM 6/3/09

   Well... the article described a pendant drop of fluid as the result of one experiment. Speaking of drops of fluid in general, all it takes to get them to run downhill is to give them a path. An upwards facing pin that intercepts the drop's surface tension, for instance, and leads to a collection device. When the droplet travels down, then the capillary is only partially filled, more action occurs to fill it, etc.
   
   Obviously there is energy coming from somewhere here, presuming this works, but it's not intuitively obvious to me *where* it's coming from.
   
   Likewise, if you use paper towels to wick up moisture, over time the high end of the towel will (if nothing else) evaporate a portion of its load and the towel will continue to wick. The rate (at least in my estimation) probably isn't sufficient to generate pendant droplets at the non-immersed end of the paper towel.
   
   Not that I've actually tried such a thing. Perhaps I should. :o)
   
   I am highly amused at the idea of a power plant made out of wicking paper towels. There's something entirely humorous about that.
   

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