Preparation of Robust, Antireflective and Superhydrophobic Hierarchical Coatings on PMMA Substrates via Mechanical Locking and Chemical Bonding.

Antireflection (AR) coatings with mechanical robustness and superhydrophobic properties have wide potential applications in optical, electronic, and automotive fields. However, the fabrication of large-sized, robust, and multifunctional AR coatings on plastic/polymer substrates has been a challenging problem. In this study, we developed a bottom-up approach to produce mechanically robust, enhanced transmittance, and superhydrophobic coatings on poly(methyl methacrylate) (PMMA) substrate. Their AR structure is composed of two layers: acid-catalyzed silica and base-catalyzed silica nanoparticles to construct a three-dimensional porous structure as the top layer; the connecting layer consists of monolayer mesoporous silica nanoparticles (MSNs) that are partially embedded in the PMMA substrate. The lower part of mesoporous silica nanoparticles is mechanically locked in the PMMA substrate by organic vapor phase treatment, while the upper part is chemically bonded to the top layer, forming a solid double-layer structure. Finally, the AR structure surface is treated by chemical vapor deposition of hexamethyldisilazane (HMDS). The obtained double-layer coating exhibits outstanding light transmission (: 98.96% in the wavelength range of 400-800 nm), superhydrophobicity (water contact angle (WCA): 157.6°, rolling angle (RA): 3.3°), mechanical robustness (pencil hardness: 4H), and weather resistance (3 months of outdoor exposure). This work offers a novel approach to the synthesis of multifunctional coatings on polymer substrates with robust mechanical properties.