State Key Laboratory of Optoelectronic Materials and Technologies and the Guangdong Province Key Laboratory of Display Material and Technology, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China.
The Ministry of Education Key Laboratory of Micro and Nano Systems for Aerospace, Northwestern Polytechnical University, Xi'an 710072, PR China.
ACS Appl Mater Interfaces. 2021 May 12;13(18):21854-21864. doi: 10.1021/acsami.1c05291. Epub 2021 Apr 28.
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.
导电水凝胶可用于与皮肤集成的可穿戴电子产品，但现有基于水凝胶的温度传感器的块状结构限制了其穿着舒适性、响应/恢复速度和灵敏度。在此，设计了基于新型薄膜夹层结构（TFSS）的可拉伸和透明温度传感器，其显示出前所未有的热灵敏度（24.54%/°C）、快速响应时间（0.19 s）和恢复时间（0.08 s）、宽检测范围（-28 至 95.3°C）、高分辨率（0.8°C）和高稳定性。薄水凝胶层（12.15 μm）被两个薄弹性体层包裹，这可以防止水分蒸发并增强热传递，从而提高了稳定性并加速了响应/恢复速度。水凝胶中加入可水合的溴化锂（LiBr）进一步提高了不干和防冻能力，使其能够避免在极其干燥的环境中脱水和在零下温度下冻结（冰点低于-120°C）。一项比较研究表明，在电容模式下，TFSS 传感器显示的热灵敏度在室温以上的传统电导/电阻模式下要高出数倍。重要的是，提出了一种基于水平板电容模型的新机制，通过考虑 TFSS 的介电常数和几何形状变化来理解其高灵敏度。薄的 TFSS、拉伸性和透明度使传感器能够贴合人体皮肤，实现各种人体运动、物理状态、皮肤温度等的实时可靠监测，而不会影响外观。
