Mechanics of Micropattern-Guided Formation of Elastic Surface Instabilities on the Polydimethylsiloxane Bilayer

The surface buckling on elastic bilayer towards a higher tunable morphological transition has attracted considerable interests. While there are many studies on the 2-dimensional analysis of surface topological changes under uniaxial plain strain, the mechanism of bifurcation remains to be understood. In this work, we investigate the surface wrinkling and the post-wrinkling bifurcation on the thin-film bilayer with a micropattern configuration at a 3-dimensional level. The pattern presents on the surface of hyper-elastic polydimethylsiloxane (PDMS) bilayer on micron scale, providing a local confinement to regulate the planar strain energy distribution. Therefore, a dedicated transition from wrinkle to post-wrinkling morphologies can be programmed. Finite element analysis further reveals that such pattern guided post-wrinkling bifurcation (i.e. main crease near the pattern edge) is caused by the stress concentration at the edge of micropattern. The simulation results uncover several subcritical features for the generation of creases: upon releasing (i.e. decreasing the overall compressive strain), they do not recover to the doubling of wrinkles at the strain level when they initiate, and a significant hysteresis is resulted. This finding will open a new window on designing and developing future smart surfaces, sensors and actuators.