Highly transparent conductive ionohydrogel for all-climate wireless human-motion sensor

Abstract

• A transparent conductive ionohydrogel was developed by employing hydrated [EMIM]Cl. • The hydrated [EMIM]Cl simultaneously provides free-ions and rich hydrogen bonds. • The ionohydrogel exhibits excellent water-retention and mechanical toughness. • All-climate ionohydrogel-based wireless sensing system was fabricated. Conductive hydrogels combined the electronic properties and soft nature of tissue-like materials can mimic the functions of human skin with mechanical and sensory properties and thus considered as one of the most promising platforms for fabricating human-motion sensors. However, the bottlenecks in inevitable water evaporation, low transparency and constraints on conductivity seriously hinder their practical application. The traditional strategies employing water-locking agent or high concentrated salt solutions are difficult to reconcile the paradox of ionic conductivity, mechanical and optical properties due to the phase separation. Herein, a novel ionohydrogel platform is prepared by employing hydrated ionic liquid as multifunctional solvent, which synchronously realize the high conductivity, transparency and wide temperature window. The multifunctional hydrated ionic liquids (HILs) ensure the ionohydrogel with high ionic conductivity (38.86 mS·cm −1 at 25 °C) and transparency (94.36% at 550 nm, 3 times of traditional hydrogels). Moreover, multiple hydrogen bonds formed by polymer chains, water and ionic liquid greatly improve the long-term stability (＞30 days) and broaden the working window (−40 °C to 80 °C). Furthermore, the wearable sensor device was fabricated through integrating ionohydrogel and silicon circuits to realize real-time motion monitoring with excellent durability (>5000 cycles) and high sensitivity ( GF = 6.78 at 800% strain). This work provides a promising and versatile method to construct the next generation of gel platform for strain sensors.