Lotus leaf inspired robust superhydrophobic coating from strawberry-like Janus particles

Abstract

We demonstrate a one-step approach toward the large-scale fabrication of robust superhydrophobic coatings using strawberry-like hemispherical Janus particles. Hemispherical Janus particles are capable of self-organizing into a layer on substrates. Nanoscale roughness on the hydrophobic hemispherical side determines the superhydrophobic performance. The imidazolin group on the hydrophilic flat side determines the coating strength by covalent binding onto substrates via cations initiating the crosslinking of the intermediate epoxy resins. The coating can tolerate organic solvents and high water flushing speeds. If the hydrophobic side is smooth, then the coating is highly adhesive to water. This procedure can fabricate unique coatings on a diverse range of substrates with varied compositions and shapes. A new coating made from self-assembling, strawberry-shaped Janus nanoparticles can turn ordinary surfaces into ultra-water-repellent materials. This first finding by Zhenzhong Yang and colleagues at the Chinese Academy of Sciences involves using a sol-gel process to synthesize tiny silica shells with ‘Janus’, or two-faced properties. Thanks to the presence of special surfactants, one side of the nanoparticle forms a curved, bumpy surface resembling that of a strawberry, whereas the other side is flat. The team modified the flat, hydrophilic surface with a reactive precursor and then sprayed an aqueous dispersion of the particles onto an epoxy-coated glass sheet. Water evaporation caused the flat silica side to covalently anchor to the epoxy, exposing a uniform coating of superhydrophobic bumps. These coatings are attractive because they are remarkably robust and could be applied to complex substrates at industrially relevant scales. Schematic synthesis of the robust superhydrophobic coating from strawberry-like Janus hemispherical particles: (a) the dispersion of aqueous particles is sprayed onto the E-51 layer on the substrate; (b) the Janus particles self-orientate to form a layer; and (c) after the epoxy resin is cured by cationic catalysis, the robust superhydrophobic coating is fabricated.