Preparation of metallic coatings with reversibly switchable wettability based on plasma spraying technology

Plasma spray technology was used for the preparation of metallic coatings with reversibly switchable wettability. By spraying Fe, Cr, and Ni mixture powders with different sizes, a micro/submicro-dual scale morphology was obtained. The resultant metallic coating had a superhydrophilic nature, but could be switched into superhydrophobic by spraying an acetone solution of dodecanoic acid while the sprayed surface remained within a temperature range of 100-200A degrees C, although dodecanoic acid itself has a hydrophilic nature. The obtained superhydrophobic coating remained stable if the temperature was below 200A degrees C. The surface wettability could further be switched between superhydrophilicity and superhydrophobicity within a time-scale of only seconds by heating above 220A degrees C and re-spraying the acetone solution of dodecanoic acid in the temperature range of 100-200A degrees C. A chemisorbed molecular layer of dodecanoic acid was responsible for the decrease of the surface energy, and the Fourier transform infrared spectroscopy (FTIR) results suggested that heating the substrate can greatly facilitate the formation of the chemisorbed layer and preferential orientation of the dodecanoic acid molecule.