NonStick drops Physicists Pascale Aussillous and David Quéré of the Collège de France in Paris have invented the ultimate oxymoron: dry water. The French researchers mixed water with water-repellent pollen grains. When dropped on a hard surface, the mix forms spherical drops with a rubbery surface. Surface tension holds the grains so tightly to the liquid that they do not rub off. As a result, these "liquid marbles" roll down an inclined surface instead of skidding like ordinary water. As they hit a maximum speed of around two miles an hour, the marbles flatten into a doughnut or peanut shape. Liquid marbles move freely on any surface--unlike water droplets, which stick as they go--so Quéré thinks they could significantly improve the operation of lab-on-a-chip devices, which test for useful new compounds by moving around tiny amounts of liquid.
Photograph courtesy of David Quéré and Pascale Aussillous/Collège de France.