Surface Modification for Superhydrophilicity and Underwater Superoleophobicity: Applications in Antifog, Underwater Self-Cleaning, and Oil-Water Separation

A facile yet effective surface modification strategy for superhydrophilicity and underwater superoleophobicity was developed by silanization of zwitterionic sulfobetaine silane (SBSi) on oxidized surfaces. The coatings exhibit excellent wetting properties, as indicated by static contact angles of <5°, and long-term stability under exposure to heat and UV irradiation. The SBSi-modified surfaces were employed for applications in antifog, self-cleaning, and oil-water separation. The SBSi glasses retained their optical transmittance because of the rapid formation of coalesced water thin films on surfaces in contact with water vapor and moisture. In addition, the underwater-oil contact-angle measurements verified the underwater superoleophobicity of the zwitterionic SBSi coatings. The oil spills on the SBSi coating could be readily removed in contact with water to realize the self-cleaning property. Besides, we modified stainless steel wire meshes with SBSi for oil-water separation. The optimal oil recovery rate for the oil-water mixtures reached >99.5% when using the SBSi-coated meshes with a pore size of 17 μm. More importantly, the water flux with modified meshes achieved 6.5 × 10⁷ L/m²·h·bar, enabling gravity-driven and energy-saving separation. Consequently, we demonstrated the superhydrophilicity and underwater superoleophobicity of SBSi, offering promise in solving technological problems of interfacial fog, oil spills, and oil-water separation and thereby showing great potential in large-scale commercial applications.