Hierarchical surface wrinkles directed by wrinkled templates

Abstract

So far, although much progress has been made in the controllable fabrication of a microstructured surface, it is still a great challenge to pattern the surface fully based on non-lithographic techniques. Here ordered hierarchical stress-relief wrinkles with well-defined microstructures have been fabricated via a template-guided surface wrinkling. The novel stable structured template is the highly oriented sinusoidal wrinkle with the tunable wavelength and amplitude, which is produced by oxygen plasma treatment of a uniaxially strained polydimethylsiloxane (PDMS) sheet followed by strain release. When the wrinkled template is conformally contacted with a polystyrene (PS) film that is coated on the compliant PDMS foundation under heating, the confinement-induced wrinkling from the template takes place on the PS–PDMS substrate. The resulting aligned wrinkles with a symmetric single mode (SSm) and symmetric double mode (SDm) are controlled by the ratio of the applied template wavelength to the film intrinsic wrinkling wavelength, regardless of the geometric feature of the underlying substrate in our case. When the template-directed wrinkling is carried out two times on the same PS–PDMS substrate, inaccessible hierarchical complex wrinkles from the well-organized SSm–SSm, SDm–SDm and SSm–SDm are obtained by means of the smart combination of the same or different wavelengths of wrinkled templates. The involved unprecedented template-induced wrinkling on the as-formed wrinkles has been discussed briefly. During the whole patterning process, the applied templates and the as-prepared structures are thoroughly based on the surface wrinkling mechanism without any lithographic method involved.