Do you fancy walking up walls like the Spiderman — the hero of millions? Technological advances have a way of catching up with our childhood fantasies, sooner or later.
A palm-sized device invented by Cornell University researchers that uses water surface tension as an adhesive bond, just might make such a dizzying feat possible.
The rapid adhesion mechanism could lead to such applications as shoes or gloves that stick and unstick to walls, or Post-it-like notes that can bear loads, says Paul Steen, who invented it.
Steen, professor of chemical and biomolecular engineering at Cornell, designed it with Michael Vogel, former postdoctoral associate.
Beetle inspiration
The device is the result of inspiration drawn from a beetle native to Florida, which can adhere to a leaf with a force 100 times its own weight, yet also instantly detach itself.
The device consists of a flat plate patterned with holes, each a millionth of a metre. 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 — much the way two wet glass slides stick together.
“In our everyday experience, these forces are relatively weak,” Steen said. “But if you make a lot of them and can control them, like the beetle does, you can get strong adhesion forces.”
For example, one of the researchers’ prototypes was made with about 1,000 300-micron-sized holes, and it can hold about 30 grams — more than 70 paper clips.
Crucial difference
They 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 1-micron-sized holes could hold more than 15 pounds.
To turn the adhesion off, the electric field is simply reversed, and the water is pulled back through the pores, said a Cornell release.
One of the biggest challenges in making these devices work, Steen said, was keeping the droplets from coalescing, as water droplets tend to do when they get close together. To solve this, they designed their pump to resist water flow while it’s turned off.
These findings were published online in the Proceedings of the National Academy of Sciences.
