The Application of MgO in Janus Fibrous Membranes Enabling Efficient Radiative and Evaporative Cooling

Passive radiative cooling presents an energy-efficient thermal management strategy requiring zero external energy input, yet conventional hydrophobic cooling membranes often trap sweat and impurities at the skin interface, diminishing comfort and cooling efficacy. To overcome this limitation, we developed an electrospun dual-layer Janus fiber membrane with asymmetric wettability that synergistically combines passive radiative cooling with directional moisture transport. The Janus architecture facilitates continuous wicking of perspiration from the skin to the environment through its wettability gradient, significantly improving thermal regulation. Magnesium oxide (MgO) nanoparticles were strategically incorporated into the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) layer, leveraging their exceptional phononic and electronic properties to achieve outstanding optical performance. The optimized membrane exhibits an average solar reflectance of 94.07% across 0.3–2.5 μm and high infrared emissivity of 90.03% in the atmospheric transparency window (8–13 μm). Outdoor evaluations demonstrated superior cooling performance compared to conventional cotton textiles, with the MgO@PVDF-HFP-PAN Janus membrane achieving an average temperature reduction of 8.7 °C and maximum cooling of 11.6 °C. Evaporative cooling experiments revealed sustained surface temperatures of 22.3 °C for the Janus membrane versus 31.6 °C for cotton, with evaporation contributing an additional 6.2 °C cooling enhancement. By integrating passive radiative cooling with evaporative cooling, this system effectively regulates heat dissipation and moisture transport, thereby enhancing thermal comfort across diverse environmental conditions.