Chameleon-inspired, dipole moment-increasing, fire-retardant strategies toward promoting the practical application of radiative cooling materials

Abstract

Toward addressing the aesthetic demand, IR emissivity, and fire hazards of radiative cooling materials in the practical application, chameleon-inspired is tactfully employed, dipole moment-increasing, and fire-retardant strategies to manufacture an advanced polyurea-based composite coating through incorporating thermochromic microcapsules, boron nitride nanosheets, and montmorillonite nanosheets. The chameleon-inspired thermochromic microcapsules and admirable IR emissivity (supported by the original IR emittance spectra) realized by the increasing dipole moment allow the composite coatings to spontaneously adjust the solar absorption and reflection during hot daytime, while enabling high-efficiency radiative cooling throughout the day. The IR emissivity higher than most literature is attributed to the strong interfacial interactions within polyurea composite coatings which improve the dipole moment of C─O─C, Si─O, and B─N bonds by increasing the distance between the centers of positive and negative charges, thus producing more IR emissions. Furthermore, the thermally melted montmorillonite nanosheets can form a ceramic protective layer enhanced by boron nitride nanosheets, further suppressing combustion behavior to improve the fire safety performance of polyurea coatings. The integration of thermochromic functionality, high fire safety, and admirable IR emissivity not only contribute to promoting the practical application of radiative cooling materials, but also provide a precious reference route to design high IR emissivity.