Ion-conductive hydrogels with intrinsic biocompatibility, stretchability, and stimuli-responsive capability have attracted considerable attention because of their extensive application potential in wearable sensing devices. The miniaturization and integration of hydrogel-based devices are currently expected to achieve breakthroughs in device performance and promote their practical application. However, currently, hydrogel film is rarely reported because it can be easily wrinkled, torn, and dehydrated, which severely hinders its development in microelectronics. Herein, thin, stretchable, and transparent ion-conductive double-network hydrogel films with controllable thickness are integrated with stretchable elastomer substrates, which show good environmental stability and ultrahigh sensitivity to humidity (78,785.5%/% relative humidity (RH)). Benefiting from the ultrahigh surface-area-to-volume ratio, abundant active sites, and short diffusion distance, the hydrogel film humidity sensor exhibits 2 × 105 times increased response to 98% RH, as well as 5.9 and 7.6 times accelerated response and recovery speeds compared with the bulk counterpart, indicating its remarkable thickness-dependent humidity-sensing properties. The humidity-sensing mechanism reveals that the adsorption of water improves the ion migration and dielectric constant, as well as establishes the electrical double layer. Furthermore, the noncontact human-machine interaction and real-time respiratory frequency detection are enabled by the sensors. This work provides an innovative strategy to achieve further breakthroughs in device performance and promote the development of hydrogel-based miniaturized and integrated electronics.
Electronic supplementary material: Supplementary material is available in the online version of this article at 10.1007/s40843-021-2022-1.
本工作中, 我们在可拉伸的弹性基底上集成了厚度可控的可拉 伸、透明的双网络导电水凝胶薄膜, 它具有很好的环境稳定性以及对 湿度极高的响应灵敏度(78,785.5%/% RH). 与块体水凝胶相比, 基于水 凝胶薄膜的湿度传感器对98% RH的响应提高了2 × 105倍, 另外, 响应和 恢复速度分别提高了5.9倍和7.6倍. 这得益于水凝胶薄膜超高的比表面 积, 丰富的活性吸附位点以及短的扩散距离. 研究发现水凝胶的湿度传 感性能具有显著的厚度依赖性. 系统的湿敏机理研究表明: 水分子的吸 附提高了水凝胶的离子迁移率和介电常数, 并且形成了双电层, 从而实 现了对湿度的超高电学响应. 此外, 该传感器能够实现非接触式人机交 互以及实时地检测人体呼吸. 这项工作为实现器件性能的突破以及推 动水凝胶基集成微电子技术的发展提供了新策略.
Keywords: humidity sensor; stretchable hydrogel; thin-film; ultrasensitive; wearable application.
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