Surface morphology and transparency control of a metal/PDMS layered substrate by stretching

We report a metal/polymer layered structure to control the transparency and surface morphology by applying strain. After a thin metal layer is coated on a PDMS substrate, the applied strain causes the micropattern on the surface to buckle owing to the difference in the elastic modulus between the metal and PDMS. When we start stretching the layered structure, the micropattern on the substrate is formed perpendicular to the direction of strain. As the substrate is stretched, the micropattern becomes wider and the substrate changes from opaque to transparent. When we stretched the substrate further by approximately 80% or more, the second buckling caused an additional micropattern in the direction of the strain. Consequently, the substrate became opaque again. We determined the mechanism based on the micropattern image and light diffraction analysis. These micropatterns change the sliding behavior of a water droplet on a slanted substrate. Moreover, the sliding speed of the water droplets was determined by the elongation rate of the substrate. We demonstrate a smart window to control the transparency and sliding speed of a water droplet using our bilayer substrate along with stretching.