Engineering surface texture and hierarchical morphology of suspension plasma sprayed TiO2 coatings to control wetting behavior and superhydrophobic properties

Beyond its conventional application for developing thermal barrier coatings, suspension plasma spraying (SPS) has shown promise for new applications focusing on surface textured coatings including superhydrophobic coatings. Such coatings have a dual-scale hierarchical morphology or so-called “cauliflower” features on the surface and they demonstrate extreme water repellence and mobility after treatment for lowering their surface energy. Studying and determining suitable process parameters to optimize the wetting properties of these coatings is the focus of this work. Herein, it is demonstrated that by carefully designing and controlling the process parameters, one can generate relatively fine and uniform dual-scale (hierarchical) surface textured coatings that after treatment for lowering their surface energy, show significantly improved water repellence and water mobility with water contact angles as high as 170° and sliding angles as low as 1.3°. It is also demonstrated that both scale levels of surface textures (i.e. micron-scale and nanoscale) are essential for having simultaneously improved water repellence and mobility. Furthermore, it is established that producing finer, more uniformly distributed and packed surface features lead to more consistent and desirable wetting properties. The results show the significant influence of pre-deposition surface roughness, precursor suspension rheology and plasma power on the structure and performance of the developed coatings.