Surface engineering with microstructured gel networks for superwetting membranes

Superwetting surfaces have several applications, such as self-cleaning, anti-fouling, anti-corrosion, water harvesting, and oil–water separation, owing to their distinct structure and properties. Hydrogel-based coatings are particularly attractive owing to their strong water affinity, hydration ability, and low oil adhesion. To further stabilize the superwetting properties of hydrogel coating, micro/nano gels possessing advantages from both hydrogels and nanomaterials can provide a larger surface area and significantly increase the surface roughness for efficient superwetting coatings on substrate surfaces. However, it is difficult to coat micro/nanogels evenly on a surface, while maintaining their original micro/nanostructure because of easy agglomeration. Herein, porous membrane substrates entrapped with precursor solutions were used in situ to form microstructured gel layers via a facile immersion-based modification method. More interestingly, by optimizing the concentration of precursor solutions, the gel microstructure shows an evolving morphology from a nanoparticle pattern to a nanoparticle-string interconnected network. The developed microstructure network layer exhibits long-term stable superwetting properties and has tolerance toward various kinds of chemicals. This layer also endows the porous membrane substrates with excellent separation efficiency for different kinds of oil-in-water emulsions, thereby producing purified water 5–10 times faster and with better oil rejection than the pristine membrane. The demonstrated facile strategy for developing a microstructured gel decoration layer may be useful for constructing other micro/nanostructured functional coatings.