Flexible humidity sensors utilizing POSS-based amphoteric ionic liquids for multifunctional wearable bio-health sensing

Recent advancements in smart medical and artificial intelligence (AI) technologies have sparked growing interest in flexible electronic devices, particularly humidity sensors for wearable and bio-health monitoring applications. Ionic liquids have been widely reported as humidity sensitive materials for flexible humidity sensors due to their strong hydrophilicity and high ionic conductivity, However, they are hindered by slow response speed and poor stability in humid environments. In this study, POSS-based amphoteric ionic liquids were synthesized by acid catalysis, and they were then incorporated into the hydrophobic polyvinylidene fluoride (PVDF) matrix for addressing above challenges of ionic liquid-based sensor. The modified PVDF/POS-Prs-TFSI humidity sensor exhibits high linearity (R 2  = 0.95), high sensitivity (0.06), fast response/recovery (0.2/14.7 s), and low hysteresis within 11 %–97 % RH (6.1 % RH), along with excellent flexibility and resistance to gas interference. The enhanced humidity-sensing performance after modification is attributed to ionic-dipole interactions occurring between the -CF₃ groups in PVDF and the imidazolium groups within POS-Prs-TFSI. Based on its excellent performance and low-cost solution processing, this sensor can be integrated into masks and skin patches for scalable production. It meets the demand for economical, high-precision humidity monitoring in consumer electronics and healthcare, enabling applications in breath analysis, skin hydration, and sweat monitoring. Additionally, it extends to plant leaf humidity detection, showing strong market potential in smart wearables, telemedicine, and precision agriculture.