Water Discovered to Flow Like Molasses
By Ben Mauk, Special to LiveScience
posted: 11 May 2007 08:58 am ET
The Taoist poet Lao Tse famously wrote that water exemplifies the highest good, benefiting all and flowing easily without effort. While this makes for a lovely metaphor, there's more to H20 than is dreamt of in Lao Tse's philosophies.
Researchers at Georgia Institute of Technology have found that, at the molecular level, water exhibits viscous, even solid-like properties.
When molecules of water are forced to move through a small gap between two solid surfaces, the substance's viscosity increases by a factor of 1,000 to 10,000, approaching that of molasses.
"In this small space between surfaces, the water, which is usually very fluid, organizes itself into a new state in which well-defined layers of molecules form," said Uzi Landmann, director of the Center for Computational Materials Science at Georgia Tech, in a phone interview with Live Science.
Layering refers to a structural phenomenon in which molecules form strata between which there is very little molecular exchange. Water molecules can move about fluidly within a single layer, but not between layers. This vertical structure resembles that found in solid substances.
Landmann directed the team of physicists that simulated the experiment and predicted the layering effect. Georgia Tech experimental physicist Elisa Riedo led the team that performed the actual experiments. Together they found that the simulation predictions matched the experimental results.
The experiment observed the properties visualized in the simulation by measuring the force required to push the solid walls together. Riedo found that the force oscillates predictably, becoming largest at the point when a layer of particles is squeezed out.
Riedo and Landmann's results stand at odds with long-held beliefs about water.
"The literature almost uniformly said that water doesn't layer," said Landmann. "Without direct evidence it was inferred that water would behave differently from those liquids that do."
Previously, experiments had not measured the force directly but rather had deduced it from other properties, since techniques at the time did not allow scientists to probe the one nanometer region required to observe the effect.
The layering phenomenon has been known for about 25 years. Hexadecanes (molecule chains of 16 carbon atoms) exhibit layering properties. These are featured in many common liquids, but not in water.
Applications for the findings can be found in fields ranging from pharmaceuticals to nanotechnology. The newfound viscosity of water suggests a cheap method for lubricating very narrow regions. Water was long thought too fluid to be useful for this purpose.
But it is not merely a matter of application, insists Landmann. "The question of the nature of materials on the small scale is itself fascinating."
On that point even Lao Tse agrees: "Magnify the small, increase the few."
Scientists Make Water Run Uphill
By Corey Binns, Special to LiveScience
posted: 29 March 2006 06:46 am ET
Toss water on a hot pan and it sizzles and evaporates. Toss water on a really hot pan, and the water beads up and starts roaming around.
Now, turn your hot pan into a hot small staircase and watch the water climb the stairs.
Researchers did just that, taking an everyday sighting in the kitchen to a new level in the lab.
How it works
If a pan's really hot, the water starts to evaporate before it even touches the surface. The evaporating water, in the airy form of a water-vapor cushion, holds the droplet above the pan. With moves as smooth as Fred Astaire, the droplet glides around on air.
When scientists heated a piece of brass with saw-tooth ridges-a thing that looks like a ratchet-water drops traveled quickly and in one direction: up.
[See the video. Credit: Heiner Linke, University of Oregon]
"The drop rides along on the vapor like a boat on a river," said physicist Heiner Linke from the University of Oregon. "The vapor is generated between the droplet and the ratchet's surface in a narrow gap, about the width of a human hair. The vapor needs a way to get out of there, and it's going to take the easiest way out. There's always going to be one direction in which it's easier to get out."
The escaping vapor pulls the droplet along in the same direction.
The research is scheduled to be published in the April 14 issue of the journal Physical Review Letters.
The traveling drops could prove helpful in cases where scientists need to cool something down with water or another liquid. Tiny air conditioners are used to cook microchips in laptop computers. But the cooling system itself requires extra energy, which creates more heat.
With the newfound trick, drops could potentially pump themselves, using heat that's already there. "Pumps that don't use moving parts are simpler to make, cheaper and live longer," Linke pointed out.
If the droplet pumps prove strong enough, Linke said they could be cooling computers in about six years.
In the meantime, schoolteachers have a new trick for the classroom.