Sticking power

 作者:甘洱琚     |      日期:2019-03-08 09:02:03
By Jeff Hecht WHAT makes sticky things sticky? Scientists say the answer partly lies in bubbles. The energy it takes to pull a finger away from a tacky surface is up to 10 000 times higher than can be explained by weak forces between molecules alone. But physicists Cyprien Gay and Ludwik Leibler of Elf Atochem in Paris have now developed a theoretical model of how a metal probe separates from a sticky film that may explain this discrepancy. Their model allows for the fact that the metal and sticky surfaces are irregular, with “valleys” 1 to 5 micrometres deep. The model shows that large and small air bubbles are trapped in the valleys when the probe and film stick together. “The bubbles can be imagined as thin lentils or discs,” says Gay. These create a suction effect when the probe pulls away from the film, making it more difficult to separate the surfaces. As the probe is pulled farther away, big bubbles swallow smaller bubbles,