Dual hydrophilic/hydrophobic SiO₂ transparent super-hydrophobic coating with good interfacial adhesion and high mechanical robustness

Water is identified as the main culprit of damage for sandstone cultural relics because of their porous intrinsic structure and nature-exposed feature. Thus, developing a super-hydrophobic coating, simultaneously with transparency, good interfacial adhesion, and robust mechanical properties, is especially critical for long-term application. However, the difficulty of balancing the contradictions between various performances is a tricky issue. Herein, tiny-level addition of amino-modified SiO₂ was used to promote the dispersibility of fluorinated SiO₂ in super-hydrophobic coating via the attachment of amino groups that was able to form hydrogen-bonding interactions, also contributing to the improved interfacial adhesion between coating and sandstone substrate. Moreover, when mass ratio of amino-modified SiO₂ to fluorinated SiO₂ reaches 1:100, the coating provides the best transparency, the optimal resistances to tape peeling, sandpaper abrasion, sand and rainwater impactions, superior than coating with perfluorinated SiO₂ particles. This mainly associates with the construction of uniform and small undulating rough surface that increases water repellency and reduces light scattering, as well as the formation of stable skeleton of “rigid-flexible” SiO₂/polydimethylsiloxane that transfers stress and dissipates energy effectively. The simple and effective strategy well solves the performance conflict and has the potential to be applied in large scale for protection of sandstone cultural relics.