Fabrication of high electroadhesion performances of thermoplastic polyurethane elastomer/metal organic framework composite films for soft grippers

Abstract Soft electroadhesion (EA) grippers which are made of soft electroadhesive materials (SEAMs) have significant applications in the fields of soft robotics and wearable devices owing to their light weight, strong force, and flexibility. However, the high EA force of SEAMs generally requires a high driving voltage (usually exceeding 2 kV), which presents problems such as electric breakdown risk and safety concerns during use. In this study, we fabricated thermoplastic polyurethane elastomer /metal-organic framework (TPU/MOF) films using two types of MOFs, ZIF-8 and UiO-66(Zr)-NH₂, and investigated the effects of MOF content on the microphase separation structure and morphology, as well as the mechanical and dielectric properties of TPU. The TPU/MOF films were applied to fabricate the EA devices by sandwiching a single compliant electrode between two layers of TPU/MOF films (SCE-TPU/MOF). The microphase separation morphology of TPU was significantly altered, and the polarization at high electric fields was improved by the addition of MOFs. The EA stress of SCE-TPU/ZIF-8 films increased with the increase of ZIF-8 content up to 0.7 phr, and reached 1085 mN/cm² of EA stress at 1 kV, which was 151% and 130% higher than that of SCE-TPU and SCE-TPU/UiO-66-0.7 (with 0.7 phr of UiO-66(Zr)-NH2), respectively. The SCE-TPU/MOF films have integrated self-bending actuation and EA capabilities, and have good durability during cycle testing. The soft gripper made from two pieces of SCE-TPU/ZIF-8-0.7 films can grasp various objects, and can lift 539 g of a glove box under 1 kV of applied voltage. Our results demonstrate that the TPU/MOF films can be achieved high electroadhesion stress using a single compliant electrode at a low applied voltage, and the SCE-TPU/MOF films have potential applications in the fields of soft grippers and medical and health devices.