Hydrothermally grown ZnO nanoarrays on phase-change core-shell fibers for solar heat-load reduction and thermal buffering

Integrating a phase-change core with hydrothermally grown optical nanostructures remains challenging because water-sensitive phase-change components may be lost or structurally damaged during aqueous mineralization. Inspired by the hierarchical leaf architecture of the Silversword, a dual scale core-shell fiber membrane was fabricated by combining coaxial electrospinning with in situ hydrothermal growth of ZnO nanorods. A PVDF-modified PEG/PAN core-shell architecture enabled the formation of a ZnO-nanorod scattering exterior while retaining the phase-transition behavior of the PEG-containing core after hydrothermal processing. This spatially separated architecture assigns distinct thermal-management roles to the two domains: the ZnO exterior reduces solar heat loading, whereas the PEG-containing core buffers transient temperature variation through reversible latent-heat storage and release.The resulting phase-change radiative fiber membrane (PRFM) exhibited a solar reflectivity of 91%, an atmospheric-window emissivity of 85%, and a melting enthalpy of 59.6 J/g. Under repeated simulated solar irradiation at approximately 1000 W/m², PRFM showed suppression of temperature rise. During the third irradiation cycle, its temperature was more than 6 °C lower than that of the control. In the outdoor device test, PRFM achieved a maximum temperature reduction of 5.3 °C relative to PAN during the high irradiance period. After 500 twisting-spreading cycles, the membrane retained 86.4% of its initial latent heat. When attached directly to the arm in the outdoor wearable test, it maintained an average temperature 4.6 °C lower than that of commercial cotton. This work provides a structural strategy for integrating optical heat-load regulation and latent-heat buffering within a single fibrous platform.