"It's true, they are small, but they are always there and we know that they are extremely reliant on distance," says Lars Johansson.
This means that the force is much stronger where the film is very close to a single high point, than when it is quite close to a number of high points. Then, when the film detaches, it does this point by point. This is because both contact surfaces are moving vibrating. These are tiny movements, but at some stage the movements are in sync, so the surfaces actually lose contact. Then the van der Waals force is so small that the film releases.
"So in reality, we can detach a thin film from the substrate simply by waiting for the right moment. This doesn't require a great deal of force. The part of the film that remains on the substrate vibrates constantly, and the harder I pull on this part, the faster the film will detach. But how long it takes for the film to detach also depends on the structure of the substrate and the film's stiffness," says Stefan Lindstrm.
In practice this means that even a small force over a long period will cause the film, or for that matter the gecko's foot, to lose its grip. Which is fine for the gecko, who can scoot off, but maybe not so good for a fastening system. Still in the right application, this knowledge can be of great industrial benefit.
|Contact: Stefan Lindström|