Bio-inspired structure using random, three-dimensional pores in the polymeric matrix for daytime radiative cooling

Inspired by the structural white of natural fibers, this work here demonstrated a novel passive radiative cooling design that builds random, three-dimensional pores in polymer matrix via the phase separation-based method. The pore size and structure are controlled by the compatibility between the shape-supporting matrix and other soluble polymers, where the semi-crystalline polypropylene (PP) was used as the shape-supporting matrix that is insoluble in any organic solvent at room temperature, and the soluble polymers were styrene-butadiene-styrene block copolymer (SBS) and styrene-ethylene-propylene-styrene block copolymer (SEPS). The experimental results revealed that those macroporous PP sheets have high solar reflectance (~97%) and tunable thermal emissivity (0.81-0.67). The outdoor thermal measurement also shows that those macroporous PP film-covered devices displayed a temperature (44.0 °C), much lower than those of air (50.0 °C) and neat-PP-covered device (60.4 °C). The complete simulation of a building thermal behavior evaluation shows that the macroporous PP roof-covered buildings exhibit a higher cooling effect than the neat PP roof-covered building in summer. Therefore, the required cooling power of the macroporous PP roof-covered buildings saved about 200 W compared with the neat PP roof-covered building on a typical summer day.