Well-defined orthogonal surface wrinkles directed by the wrinkled boundary

Abstract

In this report, we systematically investigate the as-formed wrinkles to act as a novel boundary to direct the surface wrinkling for controllable fabrication of hierarchical wrinkling patterns. Here the wrinkled boundary is the highly aligned wrinkling patterns, formed in the O2 plasma-exposed region (denoted as D1) when a uniaxially strained polydimethylsiloxane (PDMS) is subjected to the first selective O2 plasma treatment (OPT) via a copper grid. Subsequently, a stiff crust with the tunable composition is fabricated on the whole PDMS including the O2 plasma-unexposed region (denoted as D2), by means of the second OPT and/or additional film deposition (e.g., polystyrene and Pt). The subsequent solvent swelling or heating induces wrinkles in the D2 region, which are highly oriented perpendicular to those in the D1 region. The physics underpinning the experimental phenomenon is elucidated by our theoretical analysis based on Koiter's elastic stability theory and finite element simulations. Additionally, we demonstrate that the wavelengths of the well-organized orthogonal wrinkles can be independently tailored via the exposure duration and the additionally deposited film thickness.