In-drop capillary spooling and shape-memory behavior of microfiber made from self-healing thermoplastic polyurethane with supramolecular interactions and dynamic covalent bonds

Abstract

Self-autonomic repair or self-healing is a property of materials that enables them to automatically heal their surfaces from damage, such as scratches and cracks. Intrinsic self-healing has recently garnered significant attention because it can semi-permanently reform the bonds between cracked surfaces. This paper reports the synthesis of thermoplastic polyurethane (TPU) microfibers that heal intrinsically because of multiple hydrogen bonds and disulfide metathesis. The synthesized TPUs contain ureido-pyrimidinone and aromatic disulfide moieties, which form supramolecular interactions and dynamic covalent bonds. The TPU surfaces coated on glass substrates are scratched by a blade, they heal and return to their original state after heat treatment for one hour. The mechanical properties of the TPUs are maximized when the disulfide to quadruple hydrogen bond ratio is 3:7 (TPU-S3U7). Their self-healing efficiency can be improved further by adding more disulfide bonding moieties. As a result, this TPU exhibits the shape-memory effect, and the wet-spun microfibers are completely spooled by buckling into a silicone oil droplet with a diameter of 400 µm. This soft actuating materials can be applied to smart technologies such as smart textiles, smart medical implants, and soft robotics.