It is essential to impart the thermal stability, high sensitivity, self-healing, and transparent attributes to the emerging wearable and stretchable electronics. Here, a facile solvent replacement strategy is exploited to introduce ethylene glycol/glycerol (Gly) in hydrogels for enhancing their thermal sensitivity and stability synchronously. For the first time, we find that the solvent plays a key role in the thermal sensitivity of hydrogels. By adjusting the water content in hydrogels using a simple dehydration treatment, the thermal sensitivity is raised to 13.1%/°C. Thanks to the ionic transport property and water–Gly binary solvent, the organohydrogel achieves an unprecedented thermal sensitivity of 19.6%/°C, which is much higher than those of previously reported stretchable thermistors. The mechanism for the thermal response is revealed by considering the thermally activated ion mobility and dissociation. The stretchable thermistors are conformally attached on curved surfaces for the practical monitoring of minute temperature change. Notably, the uncovered Gly-organohydrogel avoids drying and freezing at 70 and −18 °C, respectively, reflecting the excellent antidrying and antifreezing attributes. In addition, the organohydrogel displays ultrahigh stretchability (1103% strain), self-healing ability, and high transparency. This work sheds light on fabricating ultrasensitive and stretchable temperature sensors with excellent thermal stability by modulating the solvent of hydrogels.

Conductive hydrogels can be used in wearable electronics integrated with skin, but the bulk structure of existing hydrogel-based temperature sensors limits the wearing comfort, response/recovery speeds, and sensitivity. Here, stretchable and transparent temperature sensors based on a novel thin-film sandwich structure (TFSS) are designed, which display unprecedented thermal sensitivity (24.54%/°C), fast response time (0.19 s) and recovery time (0.08 s), a broad detection range (from −28 to 95.3 °C), high resolution (0.8 °C), and high stability. The thin hydrogel layer (12.15 μm) is encapsulated by two thin elastomer layers, which prevent the water evaporation and enhance the heat transfer, leading to the boosted stability and accelerated response/recovery speeds. The nondrying and antifreezing capabilities are further promoted by the hydratable lithium bromide (LiBr) incorporated in the hydrogel, enabling it to avoid dehydration in an extremely arid environment and freeze below subzero temperatures (freezing point below −120 °C). A comparative study reveals that the thermal sensitivity displayed by the TFSS sensor in capacitance mode is several times higher than that in conventional conductance/resistance mode above room temperature. Importantly, a new mechanism based on a horizontal plate capacitance model is proposed to understand the high sensitivity by considering the permittivity and geometry variations of TFSS. The thin TFSS, stretchability and transparency enable the sensor to be conformally and comfortably attached to human skin for real-time and reliable monitoring of various human motions, physical states, skin temperature, etc., without affecting the appearance.

Ionic hydrogels are promising candidates for fabricating stretchable electronics, but the deficiency in drying and freezing tolerance severely limits their application. Here, we reported a facile and versatile salt-percolated strategy...

The traditional human-machine interaction mode of communicating solely with pressure sensors needs modification, especially at a time when COVID-19 is circulating globally. Here, a transparent, stretchable, resilient, and high-performance hydrogel...

A facile, one-step hydrothermal route was exploited to prepare SnO2-decorated reduced graphene oxide hydrogel (SnO2/RGOH) with three-dimensional (3D) porous structures for NO2 gas detection. Various material characterizations demonstrate the effective deoxygenation of graphene oxide and in situ growth of rutile SnO2 nanoparticles (NPs) on 3D RGOH. Compared with the pristine RGOH, the SnO2/RGOH displayed much lower limit of detection (LOD) and an order of magnitude higher sensitivity, revealing the distinct impact of SnO2 NPs in improving the NO2-sensing properties. An exceptional low theoretical LOD of 2.8 ppb was obtained at room temperature. The p–n heterojunction formed at the interface between RGOH and SnO2 facilitates the charge transfer, improving both the sensitivity in NO2 detection and the conductivity of hybrid material. Considering that existing SnO2/RGO-based NO2 sensors suffer from great vulnerability to humidity, here we employed integrated microheaters to effectively suppress the response to humidity, with nearly unimpaired response to NO2, which boosted the selectivity. Notably, a flexible NO2 sensor was constructed on a liquid crystal polymer substrate with endurance to mechanical deformation. This work indicates the feasibility of optimizing the gas-sensing performance of sensors by combining rational material hybridization, 3D structural engineering with temperature modulation.