Crack-free controlled wrinkling of a bilayer film with a gradient interface†

We report a crack-free controlled wrinkling method based on a bilayer film system. A liquid UV-curable film is solidified on a uniaxially pre-stretched PDMS elastic sheet by UV-exposure. Subsequently, the sheet is released back to its initial non-stretched state, which results in spontaneous formation of grating wrinkles perpendicular to the stretching direction. An interface of gradient interpenetrating polymer networks (IPN) is considered to be formed between the stiff UV-cured film and the elastic support, which is practically beneficial for preventing crack formation and film delamination during the strain relaxation process. The periodicity of the gratings is tuned by controlling the thickness of the UV-cured polymer film and the amplitude of pre-strain of the elastic sheet. The imprinting results demonstrate that these self-formed wrinkles can serve as a mold to duplicate gratings by nanoimprint lithography. Furthermore, metal gratings are successfully fabricated from the wrinkling molds.