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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.
