Permanent markers aren’t so permanent after all. All that’s required to peel the ink from glass is the surface tension of water and a little patience, scientists report.
When glass marked with permanent ink is slowly dipped in water, the writing lifts off the glass and floats intact atop the water. For the first time, scientists have now explained the physics behind the surprising phenomenon: The water’s surface tension breaks the seal between ink and glass, researchers report in a paper in press in Physical Review Letters.
“I think it’s amazing, the fact that they can actually peel off this layer of Sharpie with just water,” says mechanical engineer Emilie Dressaire of New York University.
Researchers stumbled upon the phenomenon by accident, when labels kept peeling off glass microscope slides during experiments. “It was just a funny observation in the lab,” says study coauthor Sepideh Khodaparast, a mechanical engineer at Imperial College London.
After recording how the process unfolds with the thin films of ink left by permanent markers, the researchers switched gears, studying another kind of film, polystyrene, because it can be produced more precisely than ink films. The ink and polystyrene films are hydrophobic — they repel water — so water resists flowing over the film, and instead works its way between the film and the glass, which attracts water. Then, the water’s surface tension can cause it to act as a wedge, separating film from glass.
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But the technique works only if the water moves very slowly — a fraction of a millimeter per second. If the water rises too fast, the wedge fails, and water passes over the film instead of peeling it.
“What is exciting about this work is that they have identified exactly under what circumstances you can optimize this process,” says physicist Kari Dalnoki-Veress of McMaster University in Hamilton, Canada. Now scientists can adapt the process to different types of films, he says.
Once removed, the floating film can be transferred to soft or delicate surfaces that might be difficult to write on directly. For example, the researchers transferred markings to a contact lens. The technique could also be used to clean surfaces without harsh solvents, and could be adapted to peel films used in ultrathin electronic devices, such as solar panels, flexible screens or wearable sensors.
THE WRITING IS ON THE WATER In this video, sped up 10 times, researchers remove permanent ink from a glass surface by slowly dipping it into water. It took about five minutes to remove the letters “P” and “U,” which stand for Princeton University, where the research took place. Khodaparast et al/Physical Review Letters 2017