Antifreezing and Nondrying Sensors of Ionic Hydrogels with a Double-Layer Structure for Highly Sensitive Motion Monitoring.

Freezing and dehydration together with interfacial failure are capable of causing the functional reduction of hydrogels for sensing applications. Herein, we develop a multifunctional bilayer that consists of a mussel-inspired adhesive layer and a functionally ionic layer that is composed of sodium -styrene sulfonate (SSS) and an ionic liquid of [BMIM]Cl. The adhesive layer enables the strong adhesion of the bilayer to the surface of the skin. The introduction of ionic elements of SSS-[BMIM]Cl not only provides the bilayer with sensing adaptability in a wide temperature range of -25 to 75 °C, but also endows it with elastic, stretchable, self-healing, and conductive features. These mechanical properties are utilized to assemble a wearable sensor that has unprecedented sensitivity and reusability in monitoring human motions, including stretching, pulsing, frowning, and speaking. It is thus expected that the concept in this work would provide a promising route to design soft sensing devices that can work in a wide temperature range.