It turns out Scotch tape curls up when exposed to humidity, so it can be used as a water-grabbing claw. This could be used to monitor water quality, according to the scientists at Purdue who developed them. The cellulose-acetate side, the slick clear film you rub with your finger, is water-absorbent. The adhesive side you stick on wrapping paper is water-repellent. So when one side absorbs water, it expands while the other side remains the same. The result is a curled-up piece of tape. Researchers led by biomedical engineering professor Babak Ziaie machined some Scotch tape so it was one-tenth of its original thickness and sliced up the pieces into four slender fingers. These were attached to a small handle that could be used to immerse the whole thing in water. They can also be deployed without a handle, curling up into tape-balls. The gripper would close in on a sample and pick it up, like a claw in one of those stuffed toy arcade games. The researchers even added some magnetic particles to the tape, so they could be retrieved with a simple magnet. Purdue doctoral candidate Manuel Ochoa came up with this idea when he was using Scotch tape for another improvised task: Picking up pollen grains. He noticed the tape curled in response to moisture. Ochoa and his colleagues were scheduled to present their findings at a Materials Research Society meeting in Boston this week. Purdue
