Electrospun polystyrene fibres on TiO2 nanostructured film to enhance the hydrophobicity and corrosion resistance of stainless steel substrates

A dual layer of dip-coated TiO2 film (top layer) and electrospun polystyrene (bottom layer) was coated on stainless steel (SS) substrates. The morphological and structural studies were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their hydrophobicity and corrosion resistance were also investigated using contact angle (CA) and electrochemical corrosion tests in acidic and salt solutions, respectively. Contact angle results showed that the naturally hydrophilic TiO2/SS sample (CA similar to 66(a similar to)) turned into a superhydrophic surface (CA similar to 148(a similar to)) when it was covered by polystyrene fibres (PS /TiO2 /SS). This observation can be attributed to the intrinsic hydrophobicity of organic polystyrene fibres (due to their low surface energy) and also to the existence of trapped air bubbles between fibres. Electrochemical corrosion tests showed that the corrosion rate was substantially decreased by using a protective bilayer (PS /TiO2) from 33 to 0.39 mV /y for bare SS sample and from 0.01 to 0.003 mV /y for PS /TiO2 /SS sample in 1 M salt and acidic solutions, respectively. The superhydrophobic protective layer forms an obstacle against ionic exchange interactions. Therefore, it slows down the breaking of the surface oxidic layer on the metal substrate and prevents the metallic surface underneath from further corrosion.