Preparing robust superhydrophobic porous coatings on rough substrates

Superhydrophobic surfaces have attracted wide attention due to their excellent waterproof performance. However, the micro-nano structural superhydrophobic surfaces are always fragile due to the poor mechanical stability. We demonstrate robust superhydrophobic surfaces with fine mechanical stability by spraying superhydrophobic coatings on rough substrates. Compared with the superhydrophobic coatings on smooth substrates (SCSS), the superhydrophobic coatings on rough substrates (SCRS) exhibit better mechanical durability because that the microstructures of the rough substrates can effectively protect superhydrophobic coatings from being destroyed under external force. The water contact angles (WCAs) of the SCRSs maintain at 152.1° ± 1.2° after 100 g sand scouring and at 139.5° ± 3.1° after 1000 g sand scouring, while the corresponding WCAs of the SCSSs will drop to 131.8° ± 2.2° and 102.6° ± 5.8°, respectively. Meanwhile, the influence of spraying process parameters on coating morphology, thickness, hydrophobicity and durability has been studied. The ratio of TiO₂ and ethyl cellulose in the coatings has been optimized, and the effects of the surface average roughness (Ra) and the coating thickness on the durability of the SCRSs have been studied. The SCRSs possess the best durability when the coating thickness is around 2/3 of the Ra of the substrate surface. The Ra of the substrate surface is fixed at 15.3μm, the durability of the SCRSs increases with the coating thickness at first. As the coating thickness exceeds 2/3 of the substrate Ra, the durability of the SCRSs decreases gradually if the coating thickness increases further. The conclusion is also verified by the SCRSs with aluminum alloys substrates under different Ra. Our work provides a feasible approach for the fabrication of robust superhydrophobic surfaces with excellent durability.