Nested self-similar wrinkling patterns in skins

We describe a simple method for generating topographically corrugated elastomeric surfaces comprising multidimensional cascades of wrinkles. These wrinkled surfaces are generated by uniaxially stretching silicon elastomer films, exposing their surfaces to prolonged ultraviolet/ozone treatment and releasing the initial strain imposed on the specimens. We show that such elastomeric artificial skins wrinkle in a hierarchical pattern consisting of self-similar buckles extending over five orders of magnitude in length scale, ranging from a few nanometers to a few millimeters. We provide a mechanism for the formation of this hierarchical wrinkling pattern, and quantify our experimental findings with both comparative computations and a simple scaling theory. Understanding the wrinkle-forming mechanism allows us to harness the substrates for applications. In particular, we show how to utilize the multigeneration-wrinkled substrate for separating particles based on their size, while simultaneously forming linear chains of equisized particles.