Stiff or Extensible in Seconds: Light‐Induced Corrugations in Thin Polymer Sheets

Abstract Corrugations can dramatically change the effective mechanical properties of a thin sheet. Such alternating ridges and grooves are typically fabricated by mechanical processing. Herein, the ability to trigger and tune corrugations within thin (≈300 µm thick) thermoplastic sheets rapidly (≈seconds) using only light is reported. Patterns of black ink on the otherwise transparent, flimsy sheet preferentially adsorb external IR light, inducing localized heating of the underlying polymer. This heating causes localized shrinkage of the polymer, producing folds in the sheets; collectively, these folds result in corrugations of controlled geometry. Depending on orientation, these corrugations dramatically increase stiffness or extensibility, similar to corrugated roofs (stiff) or accordions (extensible). In the direction parallel to the folds, the maximum load‐carrying capacity increases by two orders of magnitude relative to the non‐corrugated sheet; perpendicular to the folds, the effective modulus decreases by four orders of magnitude. In addition to tuning effective mechanical properties, the ability to corrugate flat surfaces using light has implications for assembling 3D objects from substrates printed in 2D (such as lithographically patterned electronics) or 3D structures shipped in a flat state. Herein, the process of forming such structures is discussed and their properties are characterized.