Recyclable and leakage-suppressed microcellular liquid-metal composite foams for stretchable electromagnetic shielding

The metallic conductivity and high liquidity of liquid metal (LM) make LM-polymer composites exhibit high electrical conductivity, large stretchability, and excellent mechanical-electrical decoupling, which provide significant advantages in the fabrication of stretchable electromagnetic interference (EMI) shielding materials. However, problems such as undesired LM leakage, high density, and poor recyclability due to the frequent use of chemically cross-linked polymers limit the applications of LM-polymer composites. Herein, we report the fabrication of stretchable and recyclable microcellular thermoplastic polyurethane (TPU)/LM composite foams (TLFs) with controllable LM distribution through a water-vapor-induced phase separation (WVIPS) process. The sedimentation of LM droplets helps to improve the shielding effectiveness (SE) of TLF, while the microcellular structure enables TLF with more uniform LM dispersion to achieve high leakage resistance. Moreover, the stretch-activated TLF shows high electrical stability with only slight resistance changes during stretching and exhibits a strain-insensitive shielding behavior. As a stretchable joule heater, the sample has outstanding Jouleheating performance, with stable temperature dropping only slightly under large tensile strains. More importantly, the excellent solubility of TPU, combined with a solution-based WVIPS process, allows our TLFs to be easily recycled into new products with very similar structure and performance to those before recycling, indicating the ideal recyclability of such materials.