Multifunctional Nanofiber Composites Integrating pH-Responsiveness and Passive Daytime Radiative Cooling

Abstract

Nanofiber composites integrating passive daytime radiative cooling with pH-responsiveness were developed using polyvinyl alcohol (PVA), lignin, and aluminum oxide. The composite structure was engineered to combine high solar reflectance, strong emissivity within the atmospheric window (8-13 mu m), and reversible swelling behavior in response to pH variation. Aluminum oxide nanoparticles enhance solar reflectance, whereas PVA and lignin provide functional groups enabling the formation of pH-sensitive hydrogel networks. Based on these functional groups, citric acid was introduced as a crosslinking agent to form ester bonds, thereby enhancing the mechanical strength and structural stability of the composite under aqueous conditions. The fabricated nanofiber composite exhibited excellent radiative cooling performance, characterized by high solar reflectance and strong mid-infrared emissivity. Moreover, even in the state of hydrogel, the material maintained stable radiative cooling capability under different pH environments. The independent operation of radiative cooling and pH-responsiveness enables application in diverse scenarios where passive heat dissipation and environmental sensing are both advantageous. Potential fields include biomedical systems, smart packaging, and responsive textiles, where adaptive functionality can address dynamic environmental demands. This study establishes a design strategy for multifunctional nanofiber composites that extend radiative cooling technologies into stimuli-responsive domains.