Fabrication of spatial controlled wrinkles and folds structure using stiff-ness patterning and elastic instability

Abstract

Mechanical instabilities, such as wrinkling, folding, and creasing, have long been known for one universal mechanism for the pattern formation in nature as a part of morphogenesis with various scales. A great deal of theoretical and experimental research has been devoted to understand the underlying mechanisms of mechanical instabilities and translate the phenomenon into engineering applications. Instabilities pattern has recently been exploited to form functional 3D architectures in stretchable electronics, photonic structures, and reversibly stretchable metamaterials. These applications demonstrated that instabilities pattern can be used to fabricate over large-area, highly periodic, microscale patterns without the use of rigorous and complex lithography. In this study, we suggested a new methodology to control surface structures originated from wrinkling/folding instability. Thin layered elastomer undergoes the unstable process in the presence of the compression, creating the wrinkle or fold structure. Here, we adopted the stiffness patterning methods on the surface of the elastomer to control the position of fold structure. By using conventional soft lithography, we can fabricate predefining the position of compression force on the surface by strain focalization effect. Subject to a compressive surface strain, the stiffness-patterned substrate can individually produce deformation depending on substrate stiffness. Stiffness-patterned elastic substrate was obtained by micromolding in microcapillaries (MIMIC) process. Thus the folded structure appears on the soft part of the substrate. Moreover, this new fabrication method opens the way to a new kind of microfabrication design like optical film, mechanical sensor.