Controlled 3D Shape Transformation Activated by Room Temperature Stretching and Release of a Flat Polymer Sheet

Shape transformation of polymeric materials, including hydrogels, liquid crystalline, and semicrystalline polymers, can be realized by exposing the shape-changing materials to the effect of a variety of stimuli such as temperature, light, pH, and magnetic and electric fields. Herein, we demonstrate a novel and different approach that allows a flat sheet or strip of a polymer to transform into a predesigned 3D shape or structure by simply stretching the polymer at room temperature and then releasing it from the external stress, that is, a 2D-to-3D shape change is activated by mechanical deformation under ambient conditions. This particular type of stimuli-controlled shape-changing polymers is based on suppressing plastic deformation in selected regions of the flat polymer sheet prior to stretching and release. We validated the design principle by using a polymer blend composed of poly­(ethylene oxide) (PEO), poly­(acrylic acid) (PAA), and tannic acid (TA) whose plastic deformation can be locally inhibited by surface treatment using an aqueous solution of copper sulfate pentahydrate (Cu²⁺ ink) that cross-links PAA chains through a Cu²⁺–carboxylate coordination and, consequently, increases the material’s Young’s modulus and yield strength. After room temperature stretching and release, elastic deformation in the Cu²⁺ ink-treated regions leads to 3D shape transformation that is controlled by the patterned surface treatment. This facile and effective “stretch-and-release” approach widens the scope of preparation and application for shape-changing polymers.