Tunable hierarchical wrinkling: From models to applications

Wrinkled surfaces have attracted enormous interest during the past years due to their various wrinkling patterns and impressive multifunctional properties. With the growing demand of numerous potential applications, it is desirable to uncover the formation mechanism and develop fabrication methods for tunable wrinkles, in particular, for hierarchical wrinkle that has spatially varying wavelength and amplitude. In this tutorial, we comprehensively discuss the possible mechanism of the formation of hierarchical wrinkles, including the role of elasticity gradient in film–substrate systems, the effect of boundary confinement, the sequential multistep strain-releasing method in a multilayer system, etc. The formation conditions and morphological features of various hierarchical wrinkling patterns are outlined. Lastly, representative applications of hierarchical wrinkling are briefly summarized as well.