Concentration-Dependent Pore Morphology in Cellulose Acetate Coatings for Enhanced Radiative Cooling

This study employs the non-solvent-induced phase separation (NIPS) method to fabricate porous cellulose acetate (CA) coatings. By optimizing the concentration of CA and N, N-dimethylacetamide (DMAC), the pore structure and size of the coatings are effectively controlled. The influence of homogeneous solution concentration on the optical properties of CA coatings is explored, and the relationship between the microstructure of the coatings and their radiative cooling performance is analyzed in depth. A self-assembled radiative cooling device is used to experimentally evaluate the cooling effect of the porous CA coatings. The results show that when the CA concentration reaches 15 wt%, the coating exhibits an ordered transition from irregular large pores to well-defined finger-like pores and then to sponge-like pores, achieving the optimal radiative cooling performance. At this concentration, the coating achieves a high solar reflectance (0.3-2.5 μm) of 96.56% and an emissivity of 0.96 in the atmospheric transparency window (8-13 μm). Compared to the uncoated substrate, the temperature difference reaches 18.88 °C, and the cooling effect relative to the ambient temperature is 2.6 °C, demonstrating excellent radiative cooling performance. After 10 cycles of the damp-heat cyclic test, the optical properties of the coating showed almost no change, indicating excellent damp-heat resistance.