You too can walk up walls like Spiderman, thanks to a new device invented by Cornell scientists.
The palm-sized gadget uses water surface tension to create adhesion and could be a boon for superheroes and burglars alike.
It could lead to applications such as shoes or gloves that stick and unstick to walls, or Post-it-like notes that can bear loads, according to its inventors.
The device consists of a flat plate patterned with microscopic holes. A bottom plate holds a liquid reservoir, and in the middle is another porous layer. An electric field applied by a common nine-volt battery pumps water through the device and causes droplets to squeeze through the top layer. The surface tension of the exposed droplets makes the device grip another surface, in much the way two wet glass slides stick together.
To turn the adhesion off, the electric field is simply reversed, and the water is pulled back through the pores, breaking the tiny "bridges" created between the device and the other surface by the individual droplets.
"In our everyday experience, these forces are relatively weak," said Paul Steen, professor of chemical and biomolecular engineering. "But if you make a lot of them and can control them... you can get strong adhesion forces."
So far, it's only any use for very small superheroes. For example, one prototype was made with about 1,000 300-micron-sized holes, and was able to hold about 30 grams.
But the researchers found that as they scaled down the holes and packed more of them onto the device, the adhesion got stronger. They estimate, then, that a one-square-inch device with millions of one-micron-sized holes could hold more than 15 pounds.
Steen envisions future prototypes on a grander scale, once the pump mechanism is perfected, and the adhesive bond can be made even stronger. He also imagines covering the droplets with thin membranes – thin enough to be controlled by the pump but thick enough to eliminate wetting. The encapsulated liquid could exert simultaneous forces, like tiny punches.
Steen appears to be more excited about the possible criminal applications of the device than about any plans to save the world.
"You can think about making a credit card-sized device that you can put in a rock fissure or a door, and break it open with very little voltage," Steen said. "It's a fun thing to think about."
The research behind the device is published in Proceedings of the National Academy of Sciences.