Underwater superoleophobicity, anti-oil and ultra-broadband enhanced absorption of metallic surfaces produced by a femtosecond laser inspired by fish and chameleons

Recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability

Janus wettability membranes have received much attention because of their asymmetric surface wettability. On the basis of this distinctiveness from traditional symmetrical membranes, relevant scholars have been inspired to pursue many innovations utilizing such membranes. Femtosecond laser microfabrication shows many advantages, such as precision, short time, and environmental friendliness, over traditional fabrication methods. Now this has been applied in structuring Janus membranes by researchers. This review covers recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability. The background in femtosecond laser-structured Janus membranes is first discussed, focusing on the Janus wettability membrane and femtosecond laser microfabrication. Then the applications of Janus membranes are introduced, which are divided into unidirectional fluid transport, oil-water separation, fog harvesting, and seawater desalination. Finally, based on femtosecond laser-structured Janus membranes, some existing problems are pointed out and future perspectives proposed.

High-Flux and Robust Co3O4 Mesh for Efficient Oil/Water Separation in Harsh Environment

Material with special wettability for oil/water separation has drawn more and more attention, since the oil spill accidents and industrial processing are growing in frequency and in volume. A superhydrophilic and underwater superoleophobic mesh was prepared by introducing Co₃O₄ on a stainless steel mesh, through a simple hydrothermal process and subsequent calcination. The as-prepared Co₃O₄ mesh can not only separate various oil/water mixtures with high efficiency and high flux, but also work effectively in harsh environment such as highly acidic, alkaline, and salty solutions. Moreover, the Co₃O₄ mesh can still retain good separation performance after 40 abrasion cycles with sandpaper. The outstanding anticorrosion and antiabrasion behaviors make the Co₃O₄ mesh promising for oil/water separation even in harsh environment.

Underwater Oil Droplet Splitting on a Patterned Template

Underwater oil droplets stretched and pinned by dual-dot oleophilic patterns on a superoleophobic substrate have been split into two nearly equal-volume daughter droplets using an underwater superoleophobic blade at substantially lower cutting speeds than reported in previous studies. A "liquid exchange model" based on Laplace pressure-driven liquid transport has been proposed to explain the mechanism of the underwater droplet split process. The dependence of droplet geometrical shape (curvature) and liquid properties (surface tension, viscosity) on the critical cutting speed that allows equal-volume split was investigated. Results demonstrate that critical cutting speed increases with increased curvature and surface tension of the split droplet, and decreases with increased droplet viscosity, which agrees with the proposed model. The ability to reproducibly split a single bulk oil droplet into daughter droplets with nearly equal volume facilitates the development of new functions for underwater microreactors.

Underwater Transparent Miniature "Mechanical Hand" Based on Femtosecond Laser-Induced Controllable Oil-Adhesive Patterned Glass for Oil Droplet Manipulation

Development of underwater superoleophobic surfaces has captured the imagination of researchers because of their applications; especially, oil manipulation based on such surfaces has attracted much attention. Here, we show a simple and effective way to fabricate an underwater transparent miniature "mechanical hand" based on controllable oil-adhesive patterned glass using a femtosecond laser. The underwater oil-adhesive force of the patterned glasses that compose the "mechanical hand" device can be controlled from ultralow to ultrahigh by adjusting the ratio of the untreated flat glass area to the laser-ablated rough area. These surfaces also showed favorable transparency in water. Various oils such as chloroform, hexadecane, n-dodecane, decane, liquid paraffin, and petroleum ether were tested, and their repellency against the as-prepared surfaces in water medium was confirmed. Moreover, the "mechanical hand" was used to implement oil transportation, fusion, and rapid capture, which can be applied in the construction of microfluidic devices, in situ detectors, and bioreactors.