A novel hydrophobic coating film of water-borne fluoro-silicon polyacrylate polyurethane with properties governed by surface self-segregation

The growing need of high-level anti-fouling coatings and the increasingly stringent environment regulations are demanding more versatile and eco-friendly hydrophobic materials to be developed in a facile manner. The current study considers a new water-borne fluoro-silicon polyacrylate polyurethane prepared in a two-step process as a viable candidate of green anti-fouling coating. Firstly, the water-borne fluoro-silicon polyacrylate (WFSiPA) dispersion was prepared via emulsion co-polymerization based on vinyl-terminated silicon compound and acrylate monomers containing hydroxyl, carboxyl, and fluorinated functional groups. Formulation was optimized based on studies of reaction process, emulsion stability and rheology, to achieve dispersion with a well-defined resin composition and a good leveling behavior for coating film cast. Then a water-borne isocyanate was introduced to cure the WFSiPA dispersion during the film cast whereby the two-component hydrophobic fluoro-silicon polyacrylate polyurethane (WFSiPAU) coating was produced. The surface self-segregation characteristic of fluorine (F)-segments and silicon (Si)-segments has been elucidated based on XPS and SEM-EDX analysis of the WFSiPA and WFSiPAU films, with strong F and Si enrichments on film surface and element gradient distributions across film cross-section clearly observed. The long Si-O-Si linkage structures of the segregated Si-segments induced a silicon dominance on film surface with fluorine dominated in an underneath buried layer. However, the curing reaction greatly enhanced the exposure of fluorine to the air as the siloxanne-based acrylate backbones was tightly cross-linked in the film, showing reduced surface self-segregations of the Si-segments. Moreover, the surface dominance of the F- and Si-segments and the curing governed the properties of the film, exhibiting an excellent surface hydrophobicity with an amphiphobicity potential, an enhanced thermal stability and tunable mechanical performances. Such novel coating films foresee promising applications in broad fields where hydrophobicity, antifouling and high performance are required.