Morphological transformation of a liquid micropattern on dynamically tunable microwrinkles

When a very thin, hard layer supported by a soft substrate is laterally compressed beyond a critical strain, then buckling of the hard layer occurs, leading to the formation of small sinusoidal surface undulations (microwrinkles). The orientation of the wrinkle grooves can be reversibly altered by simply adding a strain externally. Using this nonlinear microtopological change, we demonstrate that the morphology of an array of liquid filaments formed on microwrinkle grooves is dramatically and reversibly transformed into liquid filaments with a different orientation or a regular array of microdroplets, "dots", depending on the predefined contact angle. The novel liquid transformation at nanomicrometer scales will find unique applications, such as switchable light diffraction grating, laboratories-on-a-chip systems as well as a simple liquid micropatterning technique.