A Bilayer P(VDF-HFP)/SiO2 Aerogel Composite Coating on Fabric for Passive Radiative Cooling and Thermal Insulation

Abstract Passive thermal management coatings can reduce building cooling energy consumption by reflecting solar radiation and blocking heat transfer. In this work, a bilayer composite thermal management coating was designed and prepared. The coating consists of a porous poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] reflective top layer and a SiO2 aerogel/potassium hexatitanate whisker insulating bottom layer. The porous top layer was formed by water-induced phase separation. It achieved a solar reflectance of 89.2% in the solar spectral region of 0.3–2.5 μm and an infrared emissivity of 96.73% in the mid-infrared region of 3–25 μm. The bottom layer used the low-thermal-conductivity porous structure of SiO2 aerogel and the supporting effect of potassium hexatitanate whiskers, giving a thermal conductivity as low as 0.02125 W m–1 K–1. Outdoor tests showed that the bilayer composite coating achieved a maximum cooling effect of 9.9 °C. The bilayer structure enables effective cooling through the synergistic effect of solar heat input suppression by the top layer and heat conduction resistance by the bottom layer. This coating shows potential for building energy saving and outdoor thermal management.