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

Abstract

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 p-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.

Functional conductive hydrogels: from performance to flexible sensor applications

“…13c). 168 The hydrogels are treated by freezing at −25 °C and drying at 75 °C for 24 h. The sensitivities of the strain interval from 0 to 200% are 1.21 and 1.42, respectively, indicating the possibility of application under extreme conditions. This hydrogel can effectively adhere to the skin and be used to collect motion signals and recognize facial expressions.…”

“…In addition to its own adhesive properties, the adhesive function can also be directly realized by adding an adhesive layer gel into the pure conductive hydrogel. 168 A bioadhesive precursor consisting mainly of AA, AA-NHS and PVA is coated on the surface of PEDOT:PSS/PVA DNH. 165 UV curing is then performed in the presence of a photoinitiator to form an adhesive conductive hydrogel electrode (Fig.…”

“…Reproduced with permission. 168 Copyright 2022 American Chemical Society. (d) Schematic diagram of the in situ polymerization process of a doublelayer conductive hydrogel.…”

“…(c) Diagrammatic representation of internal interactions and anti-freezing and moisturizing properties of the gel for human sensing applications. Reproduced with permission 168. Copyright 2022 American Chemical Society.…”

Ultrahigh conductivity and antifreezing zwitterionic sulfobetaine hydrogel electrolyte for low-temperature resistance flexible supercapacitors

“…In particular, ice crystals can be generated inside the hydrogel at subzero temperature that can damage the exibility of the electrolytes and degrade the ionic conductivity signicantly. 22,23 To resolve this lowtemperature issue with hydrogel electrolytes, nowadays there are mainly four approaches applied (the introduction of a salt, 13 organic solvent, 24 ionic liquid, 25 or polymer network with functional groups 26 ), which essentially destroy the formation of hydrogen bonds among the water molecules and impede the formation of ice crystals, thus helping maintain the hydrogel electrolytes exibility and ionic conductivity at low temperatures. 27 However, it is difficult to achieve desirable lowtemperature capacity by only relying on the functional groups in polymer networks.…”