Wide‐Humidity Range Applicable, Anti‐Freezing, and Healable Zwitterionic Hydrogels for Ion‐Leakage‐Free Iontronic Sensors

Abstract

robots, [3] actuators, [4] etc. Among them, zwitterionic hydrogels have recently attracted tremendous attention due to their exceptional electrical properties and special biological functions, boosting progress in energy storage and biomedical applications. [5] In particular, polybetaines, bearing a pair of cationic and anionic groups in their repeating units, exhibit equal charge stoichiometry and uniform charge distribution at the molecular level. The homogenously distributed dynamic ionic bonds within the polybetaine hydrogels contribute to an efficient and rapid self-healing capability, which allows for significant deformations and autorecovery after injury during their service life. Such characteristics make polybetaine hydrogels uniquely competitive in a wide range of applications. [6] The humidity and temperature in living environment varies greatly, roughly 30-90% relative humidity (RH) and −20 to 40 °C, [7] therefore, wide-humidity range applicable and freeze-resistant hydrogels are very crucial in order to achieve reliable applications at ambient conditions. Hydrogels tend to dry out when exposed to dry environments, [8] freeze at low temperatures, [9] and swell due to water absorption in high humidity environments, [10] all of which severely affect their properties, thus limiting further applications of hydrogels in flexible electronic devices. Various methods have been reported to improve the water retention and freezing tolerance of hydrogels. Encapsulating the hydrogels can effectively prevent the Hydrogels have entered the spotlight for applications in soft electronics. It is essential and challenging to obtain hydrogels that can function properly under varying environmental circumstances, that is, 30-90% relative humidity (RH) and −20 to 40 °C due to their intrinsic nature to lose and absorb water upon variations in humidity and temperature. In this work, a green solvent, solketal, is introduced into poly 3-dimethyl-2-(2-methylprop-2-enoyloxy)ethyl azaniumyl propane-1-sulfonate (poly(DMAPS)) zwitterionic hydrogels. Compared to glycerol, solketal endows hydrogels with greater possibility for further modification as well as improved water content and mechanical performance consistency over 30-90% RH. Encouragingly, the optimized hydrogel demonstrates its unique merits as a dielectric layer in iontronic sensors, featuring non-leaky ions, high sensitivity (1100 kPa −1 ), wide humidity, and temperature range applicability. A wide-humidity range healable and stretchable electrode is attained by combining the hydrogel substrate with Ag paste. A full-device healable and highly-sensitive sensor is developed. This study is a pioneering work that tackles the broad humidity range applicability issue of hydrogels, and demonstrates the ion-leakagefree ionic skins with zwitterionic dielectrics. The outcomes of the study will considerably promote advancements in the fields of hydrogel electronics and iontronic sensors.

Conductive polymer based hydrogels and their application in wearable sensors: a review

“…However, for hydrogel-based press/strain sensors, most of them in the literature belong to resistance sensors while a minority are capacitive sensors. 30 Notably, there are few CPH based capacitive press/strain sensors as of today; we think that this is mostly due to that the sensing mechanism of the capacitive sensor is oriented from the electronic double layer (EDL) formed at the electrolyte-electrode interface, 226 while the Faraday pseudocapacitive behavior of the CPs will disrupt the linear sensing signal of the EDL capacitive sensor.…”

Ultra-robust, high-adhesive, self-healing, and photothermal zwitterionic hydrogels for multi-sensory applications and solar-driven evaporation

“…8,9 Recently, zwitterionic hydrogels, which bear equal positively and negatively charged groups in one unit, have received considerable attention owing to their characteristic structures and integrated multifunctionality, such as water retention capacity, conductivity, adhesiveness, antifouling and biocompatibility. 10 However, zwitterionic hydrogels generally suffer from poor mechanical properties due to their superhydrophilicity, which severely hinders their potential applications. 11…”

All‐Weather Self‐Powered Intelligent Traffic Monitoring System Based on a Conjunction of Self‐Healable Piezoresistive Sensors and Triboelectric Nanogenerators

“…3D hydrogels possess excellent properties in terms of stretchability, [9] self-healing, [10] flexibility, [11] and biocompatibility, [12] which are promising for triboelectrification layers and electrodes of TENGs. [13] The hydrogel-based TENG can effectively address the freezing issue in cold cities by incorporating a solvent as a partial replacement for water, thereby meeting the requirements of traffic monitoring.…”