Fabrication of superhydrophobic bilayer composite coating for roof cooling and cleaning

Building energy consumption is an important part of energy consumption. Cooling materials can be applied to reduce building energy consumption. In this study, chromium trioxide (Cr₂O₃) and titanium dioxide (TiO₂) were introduced into low-density polyethylene (LDPE) matrix to prepare the solar-infrared reflective layers, then styrene–butadiene-styrene triblock copolymer (SBS) and surface functionalized nano-silicon dioxide (SiO₂) superhydrophobic coating was constructed on the surface forming bilayer composites applying for building roof. It was found that SBS/SiO₂ coating had higher roughness, which provoked a soaring contact angle of about 160° realizing superhydrophobic surfaces. Withal, the contact angle was invariant nearly 160° after dropping the solution of calcium chloride (pH = 6), acid (pH = 2), and alkali (pH = 13) on the surface, which engendered chemical stability and anti-pollution property. Subsequently, the emissivity of LDPE and 10 wt% Cr₂O₃ composites coated with SBS/SiO₂ coating (LDPE/Cr-10/S) as well LDPE and 10 wt% TiO₂ composites coated with SBS/SiO₂ coating (LDPE/Ti-10/S) were increased to 83% and 83.9% along with high near-infrared reflectance was 47% and 63.1% separately. Simultaneously, when the initial temperature was 24 °C for 1 h under strong light irradiation in indoors, the final temperature of glass was 69 °C while the finished temperature of LDPE/Cr-10/S and LDPE/Ti-10/S were reduced to 30.5 °C and 25.8 °C respectively, showing the excellent cooling property.