Tuning the Wettability of a Commercial Silane Product to Induce Superamphiphobicity for Stone Protection

Silane-based materials are used for the protection of heritage and modern buildings. A versatile method is developed to tune the wetting properties of a typical silane-based material from hydrophobicity to superamphiphobicity, thus enhancing the protective efficacy against rainwater and organic pollutants. A commercially available silane product is blended with a fluoropolymer to lower the surface energy and silica (SiO2) nanoparticles to affect the surface morphologies of the produced coatings on marble. Contact angles of water and oil drops are measured on the coating surfaces which were prepared using 16 different combinations of fluoropolymer and nanoparticle concentrations. It is shown that the synergistic effect of surface structure and chemistry can lead to the production of coatings that possess superamphiphobic properties. The wetting properties of a selected non-wettable coating are further characterised using a custom-made, fully-automated device (Kerberos) which monitors simultaneously the deformation of the liquid interface, spreading and sliding of the drop along the sample surface during tilting. Several tests are carried out to evaluate the durability of the selected superamphiphobic coating, offering overall promising results. The versatile method can be used to impart superamphiphobicity to the surfaces of various materials. The method developed herein can be adopted to tune the wetting properties of other silane-based commercial products which are used for the protection of buildings.