Researchers at Cornell University have created a palm-sized device that uses water tension as a switchable adhesive bond and can support many times its own weight. The device could usher in a whole new generation of superheroes by allowing shoes or gloves that stick and unstick to walls on command, or see the creation of Post-It notes that can bear loads.
As reported in the Cornell Chronicle Online the device’s inventors, Paul Steen, professor of chemical and biomolecular engineering and Michael Vogel, a former postdoctoral associate, took their inspiration from Florida’s palm or tortoise beetle, which can stick to a leaf with a force 100 times its own weight by secreting an oil and pressing tens of thousands of bristles against the leaf. It can then release itself in an instant.
The device uses an electric field from a common 9-volt battery to move water through a three-layer structure. This creates surface tension which gives the device its ability to adhere. Turn off the current and the stickiness disappears.
"In our everyday experience, these forces are relatively weak," Steen told Cornell Chronicle Online’s Anne Ju. "But if you make a lot of them and can control them, like the beetle does, you can get strong adhesion forces."
A prototype device made with around 1,000 300-micron sized holes was able to hold about 30 grams (1 ounce), but the researchers found that if they scaled down the holes to cram more onto the top plate’s surface they could increase the force of adhesion. In fact they estimate that a one-square-inch device with millions of 1-micron-sized holes could hold more than 15 pounds.
The researchers’ paper, The electroosmotic droplet switch: Countering capillarity with electrokinetics, appears in Proceedings of the National Academy of Sciences.