Multifunctional strain-activated liquid-metal composite films with electromechanical decoupling for stretchable electromagnetic shielding

The increasing miniaturization and intelligence of flexible electronic devices pose a challenge to the facile and scalable fabrication of multifunctional stretchable electromagnetic interference (EMI) shielding films with strain-stable shielding effectiveness (SE). This paper presents a highly stretchable liquid metal/thermoplastic polyurethane (LM/TPU) composite film produced via a facile method of scraping and pre-stretching induced activation. The TPU matrix endows the activated LM/TPU (ALMT) film with excellent tensile properties (elongation at break >700%), and the stable and malleable three-dimensional conductive LM network enables the ALMT film to exhibit almost negligible resistance changes and strain-enhanced conductivity during stretching, resulting in excellent strain-insensitive far-field and near-field shielding capabilities. Moreover, the high EMI SE up to ∼60 dB in the tensile state (0-400%) and reduced thickness from ∼75 to ∼50 μm during stretching allow the SE/thickness values of the ALMT film to increase from ∼700 to ∼1200 dB mm, outperforming most of the reported LM/polymer composites. Furthermore, the stretchability of the ALMT film provides efficient Joule-heating performance even under substantial deformation, and it can also serve as a strain sensor for real-time monitoring of human motion. The strain-insensitive EMI shielding behavior as well as the outstanding Joule heating and sensing performance of the ALMT film renders it a promising candidate for next-generation flexible electronic devices.