Permanent markers aren’t so permanent after all, scientists now report. All you need to peel the ink from glass is water. Oh, and you also need a whole lot of patience!
When glass marked with permanent ink is slowly dipped into water, the writing lifts off the glass. It then floats intact atop the water. Scientists have now uncovered the physics behind the surprising phenomenon: The water’s surface tension breaks the seal between ink and glass.
“I think it's amazing, the fact that they can actually peel off this layer of Sharpie with just water,” says Emilie Dressaire. She is a mechanical engineer at New York University in New York City.
Researchers stumbled upon the phenomenon by accident. In the lab, labels kept peeling off glass microscope slides during experiments. “It was just a funny observation,” says Sepideh Khodaparast. She is a mechanical engineer in England at Imperial College London. She also is an author of the paper in the October 13 Physical Review Letters
The researchers first recorded how the process unfolds with thin films of ink left by permanent markers. Then they switched gears, studying another kind of film: the plastic polystyrene. A film of this can be produced more precisely than can ink films. Both ink and polystyrene films are hydrophobic, meaning they repel water. So water resists flowing over the film. Instead, it 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, gradually releasing the film from the glass.
This technique works only if the water moves very slowly. How slowly? Just a fraction of a millimeter (4 hundredths of an inch) per second. If the water rises too fast, the wedge fails. Then water passes over the film instead of peeling it away.
“What is exciting about this work is that they have identified exactly under what circumstances you can optimize this process,” says Kari Dalnoki-Veress. He is a physicist at 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 also could be used to clean surfaces without harsh solvents. It could even be adapted to peel films used in ultrathin electronic devices, such as solar panels, flexible screens or wearable sensors.
coauthor One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
glass A hard, brittle substance made from silica, a mineral found in sand. Glass usually is transparent and fairly inert (chemically nonreactive). Aquatic organisms called diatoms build their shells of it.
hydrophobic Repelling (or not absorbing) water.
lens (in optics) A curved piece of transparent material (such as glass) that bends incoming light in such a way as to focus it at a particular point in space. Or something, such as gravity, that can mimic some of the light bending attributes of a physical lens.
mechanical Having to do with the devices that move, including tools, engines and other machines (even, potentially, living machines); or something caused by the physical movement of another thing.
microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
phenomenon Something that is surprising or unusual.
physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
polystyrene A plastic made from chemicals that have been refined (produced from) crude oil and/or natural gas. Polystyrene is one of the most widely used plastics, and an ingredient used to make a widely used white, rigid foam (often sold under the name S tyrofoam).
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
slide In microscopy, the piece of glass onto which something will be attached for viewing under the device’s magnifying lens.
solvent A material (usually a liquid) used to dissolve some other material into a solution.
surface tension The surface film of a liquid caused by the strong bonds between the molecules in the surface layer.