A Self-Detecting and Self-Cleaning Biomimetic Porous Metal-Based Hydrogel for Oil/Water Separation.

Porous materials with super-wetting surfaces (superhydrophilic/underwater superoleophobic) are ideal for oil/water separation. However, the inability to monitor the pollution degree and self-cleaning during the separation process limits their application in industrial production. In this study, a porous metal-based hydrogel is proposed, inspired by the porous structure of wood. Porous copper foam with nano-Cu(OH)2 is used as the skeleton, and its surface is coated with a polyvinyl alcohol, tannic acid, and multiwalled carbon nanotube cross-linked hydrogel coating. The hydrogel has superhydrophilicity and excellent oil/water separation efficiency (>99%) and can adapt to various environments. This approach can also realize hydrogel pollution degree self-detection according to the change in the electrical signal generated during the oil/water separation process, and the hydrogel can also be recovered by soaking to realize self-cleaning. This study will provide new insights into the application of oil/water separation materials in practical industrial manufacturing.

Antifrosting Performance of a Superhydrophobic Surface by Optimizing the Surface Morphology.

Improving the antifrosting ability of stainless steel is crucial. In previous reports, many efforts have been dedicated to enhancing the antifrosting performance of superhydrophobic surface by fabricating different surface morphology. However, no researchers have proposed what kind of surface morphology can effectively prevent the frost based on the theory of superhydrophobic surfaces. In this article, we build a simulation model to study the effects of different surface morphology on antifrosting based on the Cassie model. We find that the higher the proportion of air between the droplet and the substrate, the better the antifrosting performance of the superhydrophobic surface. Therefore, we propose one superhydrophobic surface (denoted as sample #R) fabricated by selective growth. It can contain more air between the droplet and the surface. Further frosting experiments at a low temperature of -21 °C and a humidity of 75% show that 15% frost coverage on sample #R can be delayed to 63 h, as compared to less than 3 h for untreated stainless steel. In addition, the preparation method is generally applicable to other metals. Therefore, this work provides new insights into the rational design of a superhydrophobic surface with antifrosting in a harsh environment.

Drag Reduction of Anisotropic Superhydrophobic Surfaces Prepared by Laser Etching.

In this research, the anisotropic superhydrophobic surface is prepared on a stainless steel surface by laser etching, and the drag reduction property of the anisotropic surface is studied by a self-designed solid-liquid interface friction test device. Periodic arrangement structures of quadrate scales with oblique grooves are obtained on a stainless steel surface by a laser. After modification by fluoride, the surface shows superhydrophobicity and anisotropic adhesive property. Here, the inclined direction of grooves and the inverse direction are defined as RO and OR, respectively. By changing the inclination of the grooves, a surface is obtained with a contact angle of 160° and a rolling angle difference of 6° along the RO and inverse RO direction. It is verified by numerical simulation and experiment that the subjected force of water droplets on the surface is different along the RO and inverse RO direction. Furthermore, the as-prepared surface has different drag reduction effects along the two directions. With the increase of velocity, the drag reduction effect of the superhydrophobic surface decreases against the RO direction, while the drag reduction effect along the RO direction is almost unchanged. We believe the anisotropic surface will be helpful in novel microfluid devices and shipping transportation.