Highly durable amphiphobic coatings and surfaces: A comparative step-by-step exploration of the design variables

The design and production of amphiphobic surfaces with enhanced durability is increasingly considered a hot topic. It is well known that the material's repellence against liquids is regulated by morphological and chemical features of the working interfaces under different conditions. In this work the approach to the fabrication of highly repellent surfaces against both water and low surface tension oils is presented for a better understanding of the role played by different variables, e.g. the substrate surface finishing when multicomponent hybrid coatings with a different structural organization and chemistry are deposited. As suggested by biomimetic criteria, hierarchical features, when coupled with low surface energy moieties, are able to provide liquid repellence for different practical scopes. This work has been focused on coating processes applied to aluminum alloys with different surface roughness by deposition of nanostructured ceramic oxide (Al2O3, SiO2 and TiO2) and fluoro-polymers (fluoroalkylsilane or acrylic resin). It was found that the relevance of the substrate/coating variables involved in maximizing the static and dynamic liquid repellency follows the order: morphology of the inorganic layer > substrate roughness at microscale > nature of organic fluoropolymer. Both flower- and spherical-like inorganic nanostructures actually promote a significant improvement of the repellence with respect to the organic layer alone, with Al2O3 flower-like nanostructure being the most performant. Generally speaking, most hybrid-coated surfaces showed a good ability to withstand severe environments, the different response depending on the composition of the inorganic layers and not from the overall coating morphology. The step-by-step comparison of results suggests that the perspective for the application of such a kind of surfaces is related in a complex way to textural and chemical variables influencing the final performances which could stay unchanged or vary depending on the exposure environment and conditions.