Liquid-Wetting-Solid Strategy To Fabricate Stretchable Sensors for Human-Motion Detection

Abstract

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.