Physicists have experimentally demonstrated that it is possible to remove the mark of a waterproof marker pen... with water! Published in the prestigious journal Physical Review Letters, this work offers industrial perspectives for cleaning that is not aggressive and respectful of the environment.
We use water-insoluble products such as marker pen or make-up products daily. These materials, often called waterproof, allow a good resistance of the deposit by avoiding their fast dissolving under the effect of the humidity, the rain or the sweat. This good deposition may result in inconvenience during cleaning. The use of aggressive solvents or important mechanical actions is not always desirable.
An international collaboration including the Solid State Physics Laboratory (CNRS, Paris-Sud University, Paris-Saclay University) and Princeton University (USA) examined the conditions required for an hydrophobic film (who does not like water), deposited on a substrate, can be detached only ... with water. The common experience shows that by passing this sample under water, the deposit remains impassively on the substrate.
According to this original experimental study, published in Physical Review Letters, the hydrophobic film can actually come off under two conditions. First, the liquid must be "wetting" with regard to the film. Energetically, the "system" consisting of the film and the substrate must favor a situation where the film is taken off and floats on the surface. Thus, it will tend to evolve naturally towards this "taken off" state. A second condition is however necessary for this to happen: the fracture between the film and the substrate, which fills with liquid, must be able to propagate. This capacity depends on the nature of the liquid and its rate of penetration into the fracture. It must be as slow as possible so that the liquid has time to cause the detachment.
By making a mark of permanent felt on a glass slide, the researchers observed that this mark came off when the blade was dipped into a container of water at low speed, whereas this was not the case at higher speeds. This experimental study has quantitatively demonstrated the effects of viscosity and soaking rate. Subsequently, the researchers modeled these observations by expressing the energetic conditions necessary for the detachment of the film. These works offer prospects for cleaning techniques of water-proof products, with water and therefore little aggressive and environmentally friendly.
Illustration du pelage d’une écriture de feutre permanent waterproof (Sharpie) sur une lame de verre.
La lame est plongée à une vitesse de 1 μm/s.
© Laboratoire de physique des solides (CNRS/Univ. Paris-Sud/Univ. Paris Saclay)
Water-based peeling of thin hydrophobic films, S. Khodaparast, F. Boulogne, C. Poulard et H. A. Stone, Physical Review Letters (2017)