Jingming Wang

Ultrahigh Hydrogen Evolution Performance of Under-Water “Superaerophobic” MoS2 Nanostructured Electrodes

The adhesion of as-formed gas bubbles on the electrode surface usually impedes mass-transfer kinetics and subsequently decreases electrolysis efficiency. Here it is demonstrated that nanostructured MoS₂ films on conductive substrates show a faster hydrogen evolution reaction (HER), current increase, and a more-stable working state than their flat counterpart by significantly alleviating the adhesion of as-formed gas bubbles on the electrode. This study clearly reveals the importance of a nano-porous structure for HER, which should be general and beneficial for constructing other gas-evolution electrodes.

Terminating marine methane bubbles by superhydrophobic sponges.

Marine methane bubbles are absorbed, steadily stored, and continuously transported based on the employment of superhydrophobic sponges. Antiwetting sponges are water-repellent in the atmosphere and absorb gas bubbles under water. Their capacity to store methane bubbles increases with enhanced submerged depth. Significantly, trapped methane bubbles can be continuously transported driven by differential pressure.

High‐Temperature Wetting Transition on Micro‐ and Nanostructured Surfaces

With the discovery of novel wetting phenomena in nature, such as the self-cleaning effect of lotus leaves and the effortless stand and quick waterborne movement of water striders legs, surfaces with special wettability have recently attracted significant attention and have become increasingly important in our daily lives. Moreover, surface wettability at non-ambient temperature, especially at high temperature (above 100 8C), is of great importance in many industrial processes, including water transportation and metal processing, among others. Recently, several advances have been made, such as the fabrication of thermally responsive materials with controllable wettability, the repellent characteristics of different superhydrophobic surfaces to hot water, application of hydrophobic surfaces on heat exchangers at low temperature, evaporation-triggered wetting transition for water droplets on hydrophobic microstructures, and enhancement of boiling by nanostructured interfaces. The theory and applications of a liquid droplet bouncing on a hot surface in a solid–liquid heat transfer system, a very important phenomenon, have also been reported. However, the effect of chemical composition and surface morphology on the wetting behavior at high temperature (above 100 8C) has not been studied systematically. Herein, we report the investigation of the wetting behavior of surfaces with different chemical compositions and structures from 20 to 200 8C. Four kinds of microand nanostructured surfaces with different wettabilities were successfully fabricated. The wetting behavior of a water droplet was observed to be different on the surfaces, and the wetting transition (from spreading to bouncing) occurred at a specific temperature (i.e., the bouncing temperature, Tb) on hydrophilic, hydrophobic, and superhydrophilic surfaces. Surface wettability was crucial to the wetting-transition behavior, and surface roughness also affected the bouncing temperature of a surface (Tb). When surfaces with the same chemical composition got flatter, Tb decreased at the superhydrophilic surfaces and hydrophobic surfaces, while it increased at the hydrophilic surfaces. However, the spreading–bouncing transition did not take place on superhydrophobic surfaces. Silicon wafers with various structures were fabricated to investigate wettability at different temperatures. Wafers with micropillars and nanowire arrays (SiNWA) were obtained by lithography etching and chemical etching, respectively. The samples were coated with fluoroalkylsilane (FAS) to obtain hydrophobic substrates. Figure 1 shows the top-view scanning electron microscope (SEM) images and the static contact angle (CA) images of a water droplet before and after chemical modification with FAS at 25 8C. As shown in Figure 1a, b, the unmodified flat silicon and microstructured silicon surfaces (MSis) exhibited hydrophilic characteristics, and the FAS-modified MSis (FAS-MSis) were hydrophobic. Correspondingly, in Figure 1c, d, the unmodified nanostruc-

Bioinspired Gas Bubble Spontaneous and Directional Transportation Effects in an Aqueous Medium

A series of well-ordered, 3D gradient porous interconnected network surfaces composed of micro-nano hierarchical geometries is constructed on a copper wire. A continuous gas film can be trapped around its interface in an aqueous medium acting as an effective channel for gas transportation. Driving by the difference of the Laplace pressure, gas bubbles can be transported spontaneously and directionally.

Superwettability of Gas Bubbles and Its Application: From Bioinspiration to Advanced Materials

Gas bubbles in aqueous media are common and inevitable in, for example, agriculture and industrial processes. The behaviors of gas bubbles on solid interfaces, including generation, growth, coalescence, release, transport, and collection, are crucial to gas-bubble-related applications, which are always determined by gas-bubble wettability on solid interfaces. Here, the recent progress regarding the study of interfaces with gas-bubble superwettability in aqueous media, i.e., superaerophilicity and superaerophobicity, is summarized. Some examples illustrate how to design microstructures and chemical compositions to achieve reliable and effective manipulation of gas-bubble wettability on artificial interfaces. These designed interfaces exhibit excellent performance in gas-evolution reactions, gas-adsorption reactions, and directional gas-bubble transportation. Moreover, progress in the theoretical investigation of gas-bubble superwettability is reported. Lastly, some challenges are presented, such as the reliable manipulation of gas-bubble wettability and the establishment of mature theory for exactly and systematically explaining gas-bubble wetting phenomena.

Reliable manipulation of gas bubbles by regulating interfacial morphologies and chemical components

The manipulation of gas bubble behavior is crucial to gas bubble-related applications. In nature, many biological surfaces offer reliable and effective manipulation of gas bubbles in aqueous media via unusual micro/nano-hierarchical structures and chemical compositions. This inspired us to construct a series of interfaces with well-ordered microstructures and controllable chemical compositions. Reliable manipulation of CO2 gas bubble behavior can be achieved in CO2 supersaturated aqueous solutions. The CO2 bubbles generated on hydrophilic interfaces grew in situ and were then released with small diameters and spherical morphologies. The diameters of the CO2 bubbles on hydrophilic interfaces decreased as a function of interfacial roughness. FAS modification enhanced the adhesion force between the hydrophobic interfaces and the CO2 bubbles. The CO2 bubbles grew with a spherical crown shape and then coalesced with their neighbors. They finally detached and formed large diameter interfaces. As the interface hydrophobicity and roughness increased, CO2 pockets or continuous CO2 films can be created among the rough microstructures.

Effects of leading-edge bevel angle on the aerodynamic forces of a non-slender 50° delta wing

The aerodynamic performances of a non-slender 50° delta wing with various leading-edge bevels were measured in a low speed wind tunnel. It is found that the delta wing with leading-edge bevelled leeward can improve the maximum lift coefficient and maximum lift to drag ratio, and the stall angle of the wing is also delayed. In comparison with the blunt leading-edge wing, the increment of maximum lift to drag ratio is 200%, 98% and 100% for the wings with relative thickness t / c = 2%, t / c = 6.7% and t / c = 10%, respectively.

Spontaneous and Directional Bubble Transport on Porous Copper Wires with Complex Shapes in Aqueous Media

Manipulation of gas bubble behaviors is crucial for gas bubble-related applications. Generally, the manipulation of gas bubble behaviors generally takes advantage of their buoyancy force. It is very difficult to control the transportation of gas bubbles in a specific direction. Several approaches have been developed to collect and transport bubbles in aqueous media; however, most reliable and effective manipulation of gas bubbles in aqueous media occurs on the interfaces with simple shapes (i.e., cylinder and cone shapes). Reliable strategies for spontaneous and directional transport of gas bubbles on interfaces with complex shapes remain enormously challenging. Herein, a type of 3D gradient porous network was constructed on copper wire interfaces, with rectangle, wave, and helix shapes. The superhydrophobic copper wires were immersed in water, and continuous and stable gas films then formed on the interfaces. With the assistance of the Laplace pressure gradient between two bubbles, gas bubbles (including microscopic gas bubbles) in the aqueous media were subsequently transported, continuously and directionally, on the copper wires with complex shapes. The small gas bubbles always moved to the larger ones.

Reliable Manipulation of Gas Bubble Size on Superaerophilic Cones in Aqueous Media

Gas bubbles in aqueous media are ubiquitous in a broad range of applications. In most cases, the size of the bubbles must be manipulated precisely. However, it is very difficult to control the size of gas bubbles. The size of gas bubbles is affected by many factors both during and after the generation process. Thus, precise manipulation of gas bubble size still remains a great challenge. The ratchet and conical hairs of the Chinese brush enable it to realize a significant capacity for holding ink and transferring them onto paper continuously and controllably. Inspired by this, a superhydrophobic/superaerophilic cone interface is developed to manipulate gas bubble size in aqueous media. When the resultant force between the Laplace force and the axial component of the buoyancy force approaches zero, the gas bubble is held steadily by the superhydrophobic/superaerophilic copper cones in a unique position (balance position). A new kind of pressure sensor is also designed based on this principle.

The effects of apex flap on the leading-edge vortex breakdown of a cropped double delta wing

The dye-injection flow visualisation technique was used to investigate the effect of the apex flap on the leading-edge vortex breakdown over a cropped 76°/40° double delta wing. The angle-of-attack of the experimental model varied from 20° to 40°, and the length of the apex flap was 25%c and 50%c respectively