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.

Development of Self‐Folded Corrugated Structures Using Automatic Origami Technique by Inkjet Printing

“…Furthermore, the amplitude dependence of the SCS stiffness exhibited a linear scaling relationship, which is different from quadratic scaling, expressed by Equation () and in previous studies. [ 31 ] This is one of the characteristics of SCSs fabricated from flexible sheet materials and may be because the structure was not deformed by maintaining the corrugated cross section. Figure 6c presents the mountain fold parts after the three‐point bending test.…”

“…Hubbard et al fabricated corrugated structures with rectangular, square, trapezoidal, and triangular waveforms using stimuli–responsive thermoplastic sheets. [ 31 ] They conducted compression and tensile tests by varying the wavenumbers of the fabricated corrugated structures and investigated the effects of the wavenumbers on the compressive and tensile properties of the structures. However, mechanical properties were not investigated with respect to the amplitude and wavelength, which are important structural parameters of the corrugated structure when using the tailormade feature of the self‐folding methods.…”

Self-Folding PCB Kirigami: Rapid Prototyping of 3D Electronics via Laser Cutting and Forming

“…Folding can convert such planar electronics − into 3D objects to enable the production of reconfigurable devices, miniaturized components, and multiaxis sensors . In addition, devices with a third dimension can have unique or improved mechanical properties; for example, thin sheets are flexible but can be rendered stiff or extensible using corrugations . Manual folding has been used to make 3D electronic devices, ,, but this approach presents challenges for automated manufacturing and is also impossible for environments like space, so there has been significant interest in shifting to self-folding techniques. ,− …”

“…13 In addition, devices with a third dimension can have unique or improved mechanical properties; for example, thin sheets are flexible but can be rendered stiff or extensible using corrugations. 14 Manual folding has been used to make 3D electronic devices, 8,10,15 but this approach presents challenges for automated manufacturing 9 and is also impossible for environments like space, 16 so there has been significant interest in shifting to selffolding techniques. 3,17−21 Many self-folding systems rely on stimuli-responsive polymers that fold in response to heat, light, or solvents.…”

Reprogrammable Self-Folding Thermoplastic Sheets Using Elastic Filaments

“…For example, materials can be transported as flat sheets and transformed into the final product onsite. , This feature is useful when considering sending objects to outer space . Likewise, changing the shape of materials can enable efficient energy harvesting and storage, − significantly alter the effective mechanical properties of structures, and enable grippers, actuators, and 3D electronics . An ideal self-folding system utilizes stored energy to induce folding, maintains the folded shape upon removing the stimulus, and can be returned to its original shape and reprogrammed for future use.…”