Effective balance of antireflection and self-cleaning properties via hollow silica nanospheres-based surface coated with scattered titania nanoparticles

Antireflective (AR), self-cleaning, and anti-fogging bilayer coatings were prepared using a new structure and design concept. The bottom layer has a lower refractive index of 1.07-1.13 and was obtained from hollow silica (HSiO2) nanoparticles, while the top layer has a high refractive index but good photocatalytic activity via titania (TiO2) nanoparticles. The two layers give rise to a reasonable refractive index close to the ideal value of 1.22 and thus high transmittance (99.73% at maximum) in the visible region. The hardness of the TiO2 layer is a protective cover to prevent mechanical damage. This endows the surface with self-cleaning properties. In addition, the mechanical strength of the coatings was further improved due to the formation of Ti-O-Si chemical bond between TiO2 and HSiO2. The coatings also exhibit excellent super-hydrophilic and anti-fogging properties. These excellent performance features make this coating promising for applications in harsh outdoor environments. Furthermore, the coating process is simple, low-cost, and time-efficient. (C) 2015 Elsevier Ltd. All rights reserved.