High-performance radiative cooling PVDF-HFP film based on controllable porous structure

The preparation of porous films by nonsolvent-induced phase separation (NIPS) for efficient radiation cooling has attracted considerable attention. However, the thermodynamic uncertainty in the NIPS phase separation process may cause film formation to fail. Furthermore, the existing research on the pore size of porous films prepared by the phase separation method is inadequate. This study used the NIPS and vapor-induced phase separation (VIPS) techniques to ensure the stable formation of porous PVDF-HFP film (PPF). The pore size of the PPF was studied. The experimental results indicated that the film tended to obtain larger micropores at a concentration of 12 wt% and an immersion time of 12 h. The simulation results demonstrate that the scattering efficiency of 1.322 μm micropores is approximately three orders of magnitude higher than that of 0.077 μm nanopores. The porous film with the largest micropore exhibits high solar reflectivity (96.4 %) and long-wave infrared emissivity (95 %). It allows the sub-ambient temperature to drop by approximately 10.2 °C at a solar intensity of 514 W/m². It retained 96.1 % reflectivity and a porous structure, after 480 h of fluorescent lamp irradiation. This work constitutes a supplement to preparing porous films by the phase separation method.