Tunable hierarchical wrinkling surface via microscale patterned vertical deformation

Controllable nanowrinkles based on shape memory polymer (SMP) sheets have been achieved through metal deposition and subsequent heating recovery process, however, these processes cannot work without the help of macro deformation along the plane of SMP substrate. Herein, we report a simple, novel, yet more exceptional control strategy for the construction of tunable nanowrinkles based on the vertical microstress in patterned SMP surface rather than the ordinary parallel biaxial and uniaxial macro stretching. The nanowrinkling surface results from the release process of a stiffer gold film bound to the pre-stretched SMP substrate, and the pre-stretched regions are partially patterned resulting in microprotrusion arrays that contribute to the self-organization process. During the wrinkling self-organization process, the recovery of SMP surface provides the contraction microforce demanded by the nanowrinkle formation. Meanwhile, the patterned nanopillars and microprotrusions together guide the well-controlled arrangement and height achieving the micro and local control for the gold nanowrinkling patterns. Finally, the nanowrinkling and self-organization together result in the in-situ formation of nanowrinkling on gold/SMP substrate. It is the first time that micro-patterned deformation in a vertical direction was used for the fabrication of the self-organized nanowrinkling surface. This simple strategy not only provides a better understanding of local nanowrinkle formation caused by patterned prestretch substrates, but also provides a promising way to fabricate highly ordered and more complex wrinkling surfaces for various applications.