Facile fabrication of fluorine-free, transparent and self-cleaning superhydrophobic coatings based on biopolymer castor oil

A highly transparent self-cleaning superhydrophobic surface was constructed via a facile and environmentally friendly strategy by using biomass-based polyurethane and fused SiO2 nanoparticles. By simply controlling the amounts of castor oil (CO) and SiO2, the coating presented excellent superhydrophobic with high water contact angle (158.5°) and low sliding angle (3.9°), as well as the transmittance of the coating was above 80% in visible-light region. Moreover, the coatings showed remarkable robustness against abrasion of 5 cycles without an apparent decrease of superhydrophobicity and possessed excellent self-cleaning properties against dirty contaminant. Therefore, such transparent and self-cleaning superhydrophobic coating could make it an ideal material for application in optoelectronics, liquid-repellent coatings, and oil-water separation.