Superhydrophobic sol–gel nanocomposite coatings with enhanced hardness

► Hard superhydrophobic sol–gel composite coatings were fabricated using a sol of Methyltriethoxysilane and colloidal silica. ► They had a highly porous structure with nano size voids and micron size bumps. ► They exhibited very good hardness and adhesion strength with the substrate. ► Superhydrophobicity in these coatings is a combined effect of surface roughness and low surface energy due to siloxane bond network formation. Sol–gel superhydrophobic coatings with improved hardness were prepared by embedding fumed silica nanoparticles in a partially condensed hybrid sol of methyltriethoxysilane (MTEOS) and colloidal silica. Fumed silica particles of size 25–30 nm were incorporated in the sol and the mixture was spray-coated on glass substrate. Water contact angle (WCA) of the composite coating increased with increase in silica content of the sol mixture. The concentration of silica in the sol mixture was optimized to obtain robust superhydrophobic coatings with a WCA of 162.5° and a pencil hardness of 5H. The wetting state of water droplet on the sol–gel composite coatings was analysed with both Wenzel and Cassie-Baxter models.