Structured Bifunctional Fiber Membrane for Radiative Cooling with Auxiliary Sensing

This study fabricated a structured bifunctional fiber membrane integrating sensing and radiative cooling capabilities to address thermal discomfort and humidity-sensing demands during prolonged wear of protective gear. Traditional flexible polymer-based radiative cooling materials are generally hydrophobic, which significantly reduces their humidity-sensing sensitivity. In contrast, polyvinyl alcohol (PVA), though suitable for humidity sensing due to its hygroscopic hydroxyl groups, is limited in outdoor radiative cooling applications by its inherent water solubility. To solve this, a bilayer design was adopted: the outer layer is composed of polyvinyl alcohol (PVA) treated via carbon tetrafluoride (CF4) plasma etching, which not only imparts effective water resistance but also endows the fibers with high solar reflectivity and mid-infrared emissivity, achieving a radiative cooling effect of over 10 °C. The inner layer uses PVA-carbon black (PVA-CB) composites, which realize stable and rapid humidity-sensing responses via an ingenious ethanol swelling-dehydration mechanism. The PVA-CB composite fibers enable real-time respiratory monitoring with the ability to distinguish breathing patterns. By integrating cooling and sensing functions into a single membrane, this design enhances wearing comfort and compliance, reduces infection risks, and advances the development of smart medical textiles for health monitoring.