By stirring in a special powder with sloshing water, scientists created buckets of water beads that won't leak. Unlike regular water droplets that slide down a surface and leave a wet trail, these droplets can roll around and don't spill a thing.
"On a surface the coated drop rolls like a marble," says Pascale Aussillous, a physicist at the College of France in Paris and co-author with her thesis adviser, David Quere, of a recent study about the beaded, dry water in the journal Nature.
Liquid Marble Lubricants?
These "marbles" of water actually take on the properties of a spongy solid and reveal how water moves when it does not cling to surfaces. The beads' rolling motions resemble the behavior of water droplets suspended in space and, the scientists say, can lend clues about the stability and behavior of celestial bodies.
"It is interesting to study an isolated drop [of water] because it is close to the problem of an isolated planet in rotation," says Aussillous.
The dry water marbles might also carry practical applications. The French physicists suggest the dry water beads could provide a leak-free method for transporting water.
"Usually it's impossible to move small amounts of liquid without losing the matter," explains Quere. "It sticks to a surface as it moves like a tear drop."
Others suggest the beads could offer effective lubricants in tiny machines as liquid ball bearings.
What kind of high-tech powder can make liquid behave like a solid? In fact, Aussillous and Quere found the perfect material in nature. Spores of a club moss, which are primitive, veined plants, combine to create a powder with water resistent properties ? like wax or oil. The scientists then coated the spores in extra sealant to ensure they would not mix with the water.
The water resistant powder, explains Aussillous, clings only to the surface of water droplets. And since the powder blocks contact between water and a surface, the water molecules don't leak or stick to surfaces. The beads of water even float on top of a pool of regular water.
The powder and water remain separate even when the beads are punctured to release their liquid interior.
Traditionally, physicists have focused on creating surfaces that will cause water to bead and roll. Wax paper, for example, provides a surface on which water is likely to roll, not stick.
But this time, as L. Mahadevan of the University of Cambridge remarks in an accompanying column in Nature, "Aussillous and Quere have ingeniously inverted these ideas" by placing the nonstick surface around the water, rather than on the surface.
Mahadevan adds, however, that the two physicists may not be the first to think of the idea. Some insects in nature, he says, have been observed transporting tiny, powder-coated drops of water.
Tough ? for a Liquid
Mahadevan suggests coated water beads could provide wear-free lubrication for tiny machines or could lead to pipes that remain totally dry (and rust-free) while transporting gallons of beaded water.
But before any of those kinds of ideas can be explored, the team must first ensure the liquid beads are highly durable.
In tests now, the beads can reach rolling speeds of 2 meters per second (or about 4.5 miles per hour) without breaking and a coated water droplet can fall 1 centimeter (about one-fifth inch) without leaking. The water beads also resist merging ? in tests no two water beads have joined when in contact with each other.
"It is made with liquid so it is not extremely tough," says Aussillous. "But, for a drop of liquid, it is not bad."
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