High Solar Transmission Modulation and Adaptive Radiative Thermoregulation Cellulose Nanofiber Aerogel Solid–Solid Phase Change Composite for Energy-Saving Building

The development of high-performance daytime radiative cooling materials brings the negative effect of nighttime supercooling, which is a great challenge for the practical application of radiative coolers. Herein, a perpendicular-aligned cellulose nanofiber aerogel phase change composite material was prepared by a confinement polymerization strategy. The as-obtained perpCPC exhibits high transparence in the visible of 76.9%, low near-infrared transmittance of 44%, and high mid-infrared emissivity of 94.8% for daytime cooling. Significantly, the embedded phase change material absorbs ambient heat throughout hot daytime periods to augment radiative cooling, while releasing latent heat during cooler nighttime hours. Such a mechanism yields a synergistic daytime cooling effect originating from combined phase change endothermic heat capture and radiative cooling. At night, the recrystallization of the phase change material releases stored latent heat, which effectively mitigates excessive nighttime subcooling. The perpendicular-aligned cellulose nanofiber aerogel can readily demonstrate itself as a type of adaptive radiative cooling material with a temperature drop of about 11.9 °C in daytime and a temperature rise of about 3.5 °C at night.