午夜福利1000集合

SOMETIMES a water droplet is not like water at all. It鈥檚 more like a solid
ball. Two French physicists have created water droplets that aren鈥檛 wet. Dubbed
鈥渓iquid marbles鈥�, they don鈥檛 stick to surfaces and will even float on water
without breaking up.

Water droplets roll off a duck鈥檚 back because the feathers are coated with a
waxy layer that repels water. Pascale Aussillous and David Qu茅r茅
of the Coll猫ge de France in Paris wanted to create the same effect on any
surface. To do this they made water that wouldn鈥檛 stick to the surface.

They rolled droplets in a water-repellent powder鈥攍icopodium grains
coated with fluorinated silanes. 鈥淎s the powder is water-repellant, it will
not enter the liquid and will coat the outside,鈥� says 蚕耻茅谤茅.

When the powder covered the droplets, they could roll over a glass plate
without sticking to it.

This very thin layer prevents water from touching the surface, says
蚕耻茅谤茅. They retain their spherical shape and are quite stable. The
researchers report that they can even roll them across the surface of water.

鈥淚t is a very simple idea, and quite elegant,鈥� says Ralf Blossey, a
theoretical physicist at Essen University in Germany.

The researchers found that if they spun the droplets very fast, their shape
changes in an interesting way because of centrifugal forces. The droplets were
initially spherical but they become discs and then doughnuts, reports
蚕耻茅谤茅. He added that this is the first experimental verification
of a theoretical prediction made by British physicist Lord Rayleigh in 1914.

The coated droplets roll over surfaces with very little friction, so they can
be controlled by the very small forces created by electric or magnetic fields.
The researchers suggest that fields could be used to move droplets around on the
surface of a silicon chip with grooves cut in it.

With such a 鈥渕icroreactor鈥� you could mix together and study small amounts of
chemicals dissolved in the droplets . The liquid marbles can also deliver
catalysts that coat the droplets to specific locations, says
蚕耻茅谤茅.