Tuning the Wetting Properties of SiO2-Based Nanofluids to Create Durable Surfaces with Special Wettability for Self-Cleaning, Anti-Fouling, and Oil–Water Separation

Surfaces with special wettability have aroused lots of attention due to their broad applications in many fields. In this work, we systematically report selective and various fabrications of nanofluids based on readily available materials such as SiO2 nanoparticles and polydimethylsiloxane to create superhydrophobic, superoleophobic, superhydrophilic/superoleophobic, and underwater superoleophobic coatings. The efficiency of prepared coatings is investigated on mineral rock plates as porous substrates via the straightforward and cost-effective solution-immersion technique. The static water contact angle of 170°, effortless bouncing of water droplets, and self-cleaning property with a near zero tilt of the solid surface are signs of a high-performance superhydrophobic surface treated with the polydimethylsiloxane-modified silica nanofluid. The superamphiphobic nanofluid coating endows a non-adhesive feature to the rock surface by which the water and oil droplets can be freely moved on the surface with negligible tilt and are easily detached by a needle tip without leaving a trail. What is more, the superamphiphobic surface provides excellent anti-fouling and self-cleaning properties, along with convenient rolling-off behavior with sliding angles ≤8° for various oily liquids. Also, the obtained superhydrophilic/superoleophobic surface exhibits dual superoleophobicity both in air and underwater. These diverse coatings can be used on different substrates, which notably expand the scope of applications. As a case, we employed the superhydrophilic/superoleophobic coating on a stainless-steel mesh for oil–water separation. The separation efficiency of above 99% for various oil–water mixtures confirms the superior oil-shielding and water-affinity properties of the coating. All of the abovementioned advantages, combined with significant chemical and mechanical stability and high-pressure–high-temperature resistance of the treated surfaces, indicate that the prepared multifunctional coatings will hold great potential in a variety of practical and industrial applications.