A wrinkling-assisted strategy for controlled interface delamination in mechanically-guided 3D assembly

Mechanically-guided three-dimensional (3D) assembly is a recently established method for the fabrication of 3D structures and devices at micro/nanoscale. Such assembly methods typically involve a process of compressive buckling in a patterned high-modulus thin film integrated with a low-modulus elastomer substrate at selective regions. A successful assembly requires, simultaneously, a sufficiently strong interface in selective regions to stay undelaminated, and a sufficiently weak interface in remaining regions to be fully separated. However, such requirements are very challenging to meet for highly flexible 3D mesostructures or those with large-area suspended features. Here, we propose a wrinkling-assisted strategy to substantially facilitate the delamination at desired regions of the film/substrate system. An additional assisting layer is introduced such that a weaker film/assisting-layer interface replaces the original film/substrate interface, and the wrinkles formed in the assisting layer induce additional driving forces to separate the film/assisting-layer interface. An analytical model is developed to capture the delamination of the thin film from the wrinkled assisting layer, which is validated by both experiments and finite element analyses (FEA). The model shows that a combined material/geometry parameter governs the process of delamination in the bilayer film/substrate system, offering a useful design reference for the mechanically-guided 3D assembly. Furthermore, our experiments and FEA demonstrate that the wrinkling-assisted strategy can enable the assembly of highly flexible 3D mesostructures and those with large areas attached to the substrate in the initial configuration, which are particularly challenging to achieve by using previous strategies.