Spatially configuring wrinkle pattern and multiscale surface evolution with structural confinement

Surface elastic instabilities, such as wrinkling and creasing, could enable a convenient strategy to impart reversible patterned topography to a surface. Here we focus on the classic system of a stiff layer on a soft substrate, which famously produces parallel harmonic wrinkles at modest uniaxial compression that period-double repeatedly at higher compressions and ultimately evolve into deep folds and creases. By introducing micron-scale planar Bravais lattice holes to spatially pattern the substrate, we can guide these instabilities into a wide variety of different patterns, including wrinkling in parallel bands and star shape bands, and radically reduce the threshold compression. We are able to understand our experimental patterns and thresholds by considering a simple plane-strain model for the patterned substrate-deformation, decorated by wrinkling on the stiff surface layer. Our experiments also show localized wrinkle-crease transitions at modest compression, yielding a hierarchical surface with different generations of instability mixed together. By varying the geometrical inputs, we demonstrate control over the stepwise evolution of surface morphologies. These results demonstrate considerable control over both the patterns and threshold of the surface elastic instabilities, and have relevance to many emerging applications of morphing surfaces, including in wearable/flexible electronics, bio-medical systems and optical devices.