Liquid-wetting-solid strategy to fabricate stretchable sensors for human-motion detection

The inherent limitation of stretchable conductor design is mechanical mismatch, because typical Young's moduli of inorganic conductors are 5-6 orders of magnitude larger than that of the soft elastomers - leading to material delamination and/or local fracturing under large strains. To address this challenge, we report a simple yet general liquid wetting solid strategy to fabricate stretchable conductors, which can overcome the aforementioned challenges. Our approach - utilizing ionic liquids (ILs) as the conductive components - is conceptually different from traditional metals/polymers (briefly rigid-on-soft type) construction, since we employ a lower Young's modulus conductive liquid to integrate with elastomers (briefly soft-on-soft type). It is also different from previously reported liquid metal strategy, in which high surface tension limits the scope of applications. Our IL-based strategy is universal and applicable to different hydrophilic/hydrophobic IL species, and able to turn diverse soft elastomeric supports into stretchable conductors in a simple and rapid manner. The IL-based conductors exhibit exceptional performance - functioning at ultralarge strains (ϵ > 600%); high sensitivity down to a low-strain of 0.05%; high durability with negligible loading-unloading signal changes over 10 000 cycles. In addition, skin-attachable and cloth-integratable features allow a wide range of human-motion detections. We envision that this liquid-wetting-solid strategy will be promising on the large-scale fabrication of stretchable electronics, personal health monitoring, and "smart" electrical skins for soft robots and prosthetics.