A self-adjusting PTFE/TiO2 hydrophobic double-layer coating for corrosion resistance and electrical insulation

The self-adjusting polytetrafluoroethylene (PTFE)/TiO2 organic-inorganic double-layer coatings are designed on titanium alloy using thermal field and gradient pressure field enhanced plasma electrolytic oxidation (TGEPEO), which leads to the in-situ incorporation of PTFE nano-particles into the bottom TiO2 ceramic coating. The PTFE top layer with adjustable thickness is strongly bonded on a TiO2 bottom porous layer by subsequent deposition, chemical bonding and crosslinking curing of PTFE nanoparticles during TGEPEO process. Simultaneously, the double-layer coating possesses promising self-cleaning function due to a special hydrophobic surface with a water contact angle of 138.0 +/- 4.4 degrees caused by self-adjusted surface micro-nano structure. Moreover, the PTFE/TiO2 double-layer coating exhibits excellent corrosion resistance and high electrical insulation. More importantly, the microstructure of the double-layer coating underwent self-adjustment in long-term immersion, caused by the accumulation-redeposition of corrosive ions and the closure of the reticular microchannels at the damaged regions, thus enhancing long-term chemical stability.