A Surface Exhibiting Superoleophobicity Both in Air and in Seawater

Superoleophobic surfaces have attracted increasing interest in recent years due to their potential application in various fields. In this paper, we report a surface that exhibits superoleophobicity both in air and in seawater. A polyelectrolyte multilayer (PEM) is assembled on an aluminum substrate with a micro/nano hierarchical surface structure, and the counterion in the PEM is exchanged with perfluorooctanoate (PFO), making the surface superhydrophobic and superoleophobic in air. When submerged in artificial seawater, the surface exhibits underwater superoleophobicity, with a 1,2-dichloroethane contact angle of 163 degrees. X-ray photoelectron spectroscopic analysis and controlled experiments reveal that, upon exposure to seawater, the PEM spontaneously exchanges the PFO counterion with the chloride and sulfate ions in the seawater, making the surface hydrophilic and hence oil-repelling underwater. When withdrawn from seawater, superoleophobicity in air is restored by treating the surface in a PFO solution shortly to reinstall the PFO counterion. The switching between the two wetting states (superoleophobicity in air and underwater) is completely reversible. This simple and versatile approach can be readily extended to other substrates, making it a promising method for introduction of dual superoleophobicity to surfaces used in many fields.