Control of Surface Wrinkling through Compliant Nanostructured Interfaces

Surface wrinkling occurs due to the mechanical instability induced by the stiffness mismatch between a soft substrate and a stiff film. In a two-layer system comprised of a thick compliant substrate and a thin stiff film, the wrinkle pattern, as described by the wrinkle wavelength, amplitude, and orientation, is limited by the material properties and thickness of the two layers. In this work, an interface layer of nanostructures fabricated by glancing angle deposition (GLAD) is introduced to modify the surface wrinkling of polydimethylsiloxane due to a Cu film, thus enabling improved control of wrinkling in an otherwise constrained material system. Isotropic (nanospring) and orthotropic (nanochevron) Cu interfaces are GLAD-deposited with different geometric parameters to control the in-plane stiffness of the interface. The isotropic nanospring films provide a novel means to control the physical length scale of wrinkle patterns, namely, both the wavelength and the amplitude of surface wrinkles, while maintaining the amplitude-to-wavelength aspect ratio. The anisotropic nanochevron films result in anisotropy ratio of ≈10 which provides a unique means to modify the wrinkle direction independently of the direction of the applied load. The prediction by the experimentally calibrated analytical model is shown to be in good agreement with the experiment.