Nanocellulose/Poly(vinyl alcohol)@Phase Change Microcapsule Aerogel Inspired by Wood for Adaptive Radiative Cooling in Buildings

Radiative cooling, as an emerging energy-saving technology, can achieve zero-energy passive cooling. However, existing research has focused only on enhancing radiative heat dissipation, resulting in severe overcooling at night and difficulty in adapting to daytime temperature fluctuations. Combining radiative cooling materials with phase change energy storage materials can effectively address this problem. Inspired by the layered porous structure of wood, this study selected carboxylated nanocellulose and poly(vinyl alcohol) as the aerogel matrix and used directional freezing technology to form vertically aligned channels that mimic the orientation of wood microfibers. Subsequently, phase change microcapsules synthesized via the Pickering emulsion method were integrated. This integrated design achieves dual functions: during the day, the high solar reflectance (96.94%) and high emissivity (94.67%) of the biomimetic structure work synergistically with the endothermic effect of the phase change material, enabling the aerogel to achieve efficient cooling with an average temperature reduction of 10.6 °C; at night, the phase change material releases stored heat to mitigate overcooling with an average temperature increase of 2.2 °C. In addition, the directional freezing process endows the aerogel with lightweight and high-strength properties (compressive strength of approximately 35 MPa), making it suitable for building insulation layers. This study achieves the synergistic integration of radiative cooling, phase change energy storage, and biomimetic structural design, providing an efficient and stable solution for adaptive building thermal management and promoting the practical application of “zero-energy buildings.”