A thin film wrinkles differently depending on its thickness and elasticity—just as a prune forms wider, deeper wrinkles the thicker or less flexible its skin is.
In this image, a droplet of water rests on a polystyrene film a quarter of a micron thick, itself floating on water. Surface tension pulling the droplet into a roughly hemispherical shape also creates an inward pull on the film. The film wrinkles to fit its unchanged surface area into less space. In the Aug. 3 Science, Thomas Russell of the University of Massachusetts in Amherst and his colleagues show that the number and length of wrinkles is an accurate indicator of the film’s characteristics. Russell says that the technique could measure how the elasticity of a film changes as its thickness decreases to nanoscale dimensions.