Humble cellophane tape is 'smart' material

Clear cellophane adhesive tape, the household package-wrapping essential, may have applications as a shape-changing "smart material," U.S. researchers say. Scientists at Purdue University used a laser to form slender half-centimeter-long fingers out of the tape that, when exposed to water, shape-changed into a tiny robotic claw capable of capturing water droplets. The innovation could be used to collect water samples for environmental testing, engineering Professor Babak Ziaie said. Clear cellophane tape, made from a cellulose-acetate sheet and an adhesive, is uniquely suited for the purpose, he said. Doctoral student Manuel Ochoa came up with the idea, noticing what happened to the tape when it is exposed to humidity. The cellulose-acetate absorbs water, he found, but the adhesive film repels it. "So, when one side absorbs water it expands, the other side stays the same, causing it to curl," Ziaie said. The tiny tape "grippers" close underwater within minutes and can sample one-tenth of a milliliter of liquid, the researchers said.