Fabrication of micro-/nano-structured super-hydrophobic fluorinated polymer coatings by cold-spray

A fabrication of superhydrophobic Perfluoroalkoxy Alkane (PFA) coatings on stainless steel surfaces by cold-spray technique has been demonstrated in this work. The in-situ supersonic impact deposition and consolidation of finely divided 20-40 mu m powder material yielded hydrophobic thin coatings of PFA which exhibited contact angles of 125 degrees but high roll off angles of 60 degrees. The deposition efficiencies were less than 0.5%, coating was mechanically very fragile and non-uniform. However, the cold-spray deposition efficiency was subsequently increased to almost 15% by performing simple modification of particle surface morphology by introducing organosilane coated nanoceramic layers on the PFA particles and by laser texturing the stainless steel substrate surfaces to form mountain-valley micro-structures. The nanoceramic interlayers formed bridge bonds at the particle-particle interface and laser texturing achieved efficient coating-substrate interlock. The improved coatings exhibited super-hydrophobic character with 160 degrees contact angle and 6 degrees roll-off angle. The super-hydrophobicity was seen to be as a result of micro-/nano-structured surface consisting of papillae like structures capped by a layer of hydrophobic nanoceramic. The coating also exhibited excellent water repellency.