Superhydrophobic alkoxysilane/T-ZnO/SiO2 nanocomposite coatings enhance mechanical properties of porous building substrates: An experimental and multi-physics simulation study

The great promise of superhydrophobic surfaces for broad functional applications has attracted enormous attention, yet their poor durability, potential pollution/health risks and lack of mechanical reinforcement effects for porous substrates impede the application. This work reports superhydrophobic coatings that also enhance the mechanical strength of substrates, fabricated via a one-step fluorine-free preparation and tunning molar ratios between trimethoxyoctylsilane (TMOS), ZnO tetrapods (T-ZnO) and SiO2 nanoparticles. The as-synthesized TMOS/SiO2/T-ZnO= 3/1/1 coating demonstrates the highest surface roughness (23.66 mu m), hydrophobicity (166 degrees), and antimicrobial efficacy against Gram-positive/-negative bacteria (82 % and 78 % respectively, at the concentration 2.0 g/L). The isotropic high mechanical and chemical strength of T-ZnO in 3D improves the surface roughness and erosion/abrasion resistance (withstand up to 100 cycles). Moreover, micro-drilling tests show that as-prepared coatings endow porous substrates with additional mechanical strength. The self- condensation of TMOS in the presence of T-ZnO and SiO2, which act as 3D skeleton fillers inside the gelled silica networks, contributes to mechanical strength improvement. Furthermore, the multi-physics simulations reveal that the diffusion capability of coatings and the resulting relative concentration determine their mechanical property. With the facile synthesis and versatility, this work offers an eco-friendly preparation route for multi-functional surfaces, broadening the application and promoting large-scale production.