Three-Axial Strain-Triggered Multimode Wrinkles with Tuneable Frictional and Optical Performances.

Wrinkled surfaces driven by stresses/strains are very common in living bodies and geologic structures. The nature-inspired wrinkle patterns have great application prospects in the fields of microfluidics, flexible electronics, smart optics, adhesion, and sensors. Although various wrinkles with single features such as stripes, herringbones, labyrinths, hierarchies, and periodic arrays have been extensively reported, achieving multimode wrinkles in a single sample with large scales is still a challenge. Here, we develop a facile technique to prepare controllable multimode wrinkles in flexible film systems by simply applying three-axial strain. It shows that striped, rippled, and labyrinth-like wrinkles spontaneously form at corners, edges, and center of the triangular film sample, respectively. The morphological characteristics, transition behaviors, and formation mechanisms of such multimode wrinkles are investigated by the experiment, stress theory, and finite element simulation. The frictional and optical performances are obviously anisotropic at the corners and edges, but are isotropic in the center, exhibiting a strong dependence on the wrinkle features. The diffraction properties of light are also well tuneable by exerting mechanical strains. This study helps better understand the wrinkle patterns under three-axial strain and provides a novel way to tailor multimode wrinkles for practical applications.