Biomimetic all-weather dual-mode cooling film for passive heat dissipation

Passive radiative cooling technology offers a zero-carbon comfort solution for maintaining comfortable ambient temperatures. However, single-mode passive radiative cooling is significantly weakened by the shielding effect of high-humidity environments. Inspired by the thermoregulatory mechanisms of plant leaves, we designed a dendritic structure amino-functionalized cellulose (ACE) for passive heat dissipation. ACE provides abundant amino groups and Schiff base sites, which not only enhance interactions with water molecules through hydrogen bonding but also facilitate solar radiation absorption via the stretching vibrations of the imine bonds (-C = N-). Leveraging these properties, an ACE@PVA dual-mode cooling film was fabricated using self-assembly technology. Despite its ultrathin profile (80 µm), the film achieves a hygroscopic capacity exceeding 3.32 ± 0.36 g/g and a solar reflectivity of 43.6 ± 2.1%. Under outdoor conditions, the film demonstrated excellent passive cooling performance, achieving subambient cooling of 4.7°C to 13.7°C during daytime and 4.3°C at night. This ultrathin, dual-mode cooling film is well suited for dynamic seasonal and weather variations, offering significant potential for mitigating the energy crisis and reducing greenhouse gas emissions.