Reprogrammable Three-Dimensional Configurations Using lonomer Bilayers

An approach for various programmable 3D structures based on commercially available perfluorinated sulfonic-acid ionomers (PFSAs) is presented. The uniaxial stretching induces the hydrophilic channels of PFSA to align along the stretching direction, leading to anisotropic swelling behavior. A bilayer composed of two stretched PFSA membranes with perpendicular orientation morphs within just a few tens of seconds into useful shapes including twisted helices, cylindrical helices, and rings in swollen state depending on the cutting angle and dimensionless width, similar to prior studies on chiral seedpods. Especially in the wide width regime, where the stretching energy is dominant to the bending energy, two different configurations sharing the same handedness are both stable and provide multiplicity in shape selection from a single strip through spatial dependent swelling-deswelling cycles. Using the non-Euclidean geometries from 2D ionomer bilayers, macroscopic humidity-sensitive actuators, various 3D structures, and bistable self-folding structures are demonstrated. This facile fabrication approach for various structures with commercially available ionomers will provide possible applications for humidity-sensitive, ion-conductive actuation systems in the future.