How wet paper curls
Physique et Mécanique des Milieux Hétérogènes, UMR 7636 du CNRS, ESPCI - 10 rue Vauquelin, 75005 Paris, France, EU
2 Engineering and Applied Sciences, Wyss Institute, Harvard University - 29 Oxford St, Cambridge, MA 02138, USA
Accepted: 9 February 2011
When a piece of tracing paper is placed gently on the surface of a bath of water, it rapidly curls up from one edge and rolls up due to the swelling of the side in contact with water. With time, as the swelling front propagates through the thickness of the paper, the paper gradually uncurls itself and eventually straightens out. We analyze the experimental dynamics of rolling and unrolling of the paper and complement these with a minimal theory that explains the basic observations. Our study might be useful in the context of designing biomimetic devices that work as actuators or harness energy from humidity variations.
PACS: 46.70.De – Beams, plates, and shells / 82.30.Rs – Hydrogen bonding, hydrophilic effects
© EPLA, 2011