Self-healing, anti-freezing and highly stretchable polyurethane ionogel as ionic skin for wireless strain sensing

Due to the ability to reliably convert stimuli into electrical signals, ILs-based ionogel devices are of great importance in artificial sensors, wearable devices and soft robots. Yet profound challenges remain in enabling wearable devices to maintain their characteristics under extreme conditions (sub-zero temperatures or long-time storage). To address this issue, an anti-freezing ionogel for multimodal artificial skin was fabricated on the basis of ILs and PU network. The resulted PU ionogel showed superb stretchability (approximately 390%), great self-healing ability (self-healed in 30 min at room temperature), and high conductivity (~14 mS cm−1). More importantly, these well-designed ionogels possessed a relatively high sensitivity at strains of 0.1 to 200% and pressures of 0.1 to 20 kPa. The PU ionogels also exhibited a highly repeatable sensitivity over 5000 unremitted strain cycles. Ionogels reserved at −20 °C for 10 days or in a normal environment for 15 days have almost the same sensing capability as the fresh ionogels. The ultra-durability of the PU ionogels results from the combination of ILs (non-volatility and great conductivity) and PU network (excellent healability, and mechanical properties). The cracked PU ionogels can also be facilely self-healed at room temperature owing to the reversible boronic ester bonds, and then restore their original sensing performance.