Preparation of transparent and robust superhydrophobic surfaces for self-cleaning applications

Superhydrophobic surfaces have recently attracted a lot of attention due to their high water repellency along with a wide range of applications in many fields. The application of such surfaces for self-cleaning purposes, such as in solar cell modules, has been limited due to the lack of mechanical robustness, thermal stability and ultraviolet radiation resistance. The fabrication of superhydrophobic water-repellent surfaces with mechanical robustness and high transmittance remains a major challenge. This paper presents a method for fabrication of transparent, robust and stable superhydrophobic surfaces by simple spray coating process. The developed coating solution can be sprayed on all kinds of materials to create a superhydrophobic self-cleaning surface. Proper molar ratios of Methyltrimethoxysilane (MTMS) and (3-Glycidyloxypropyl)trimethoxysilane (GLYMO) are used to bond the functionalized silica nanoparticles to various substrates and promote robustness. Optimum spraying cycles (layers) of 1.0%wt SiO₂ nanoparticles after adhesive layer has resulted in contact angles of the order of 170˚ with a hysteresis of 6° and sliding angle of 1°. Developed surfaces also exhibited excellent stability under pressurized jet water, abrasion and ultraviolet radiations. Improvement of surface transmittance was achieved by annealing the surface under temperatures up to 300 °C without losing superhydrophobicity. The optical transmittance of the optimum annealed surface varied between 75% of that of virgin glass, at the visible light wavelength of 400 nm and 90% at 800 nm. The unique combination of the above-mentioned desired properties of the fabricated surface, makes them a promising candidate for outdoor self-cleaning applications even under harsh environmental conditions.