The major drawback of current passivation techniques for preventing corrosion is the lack of ability to withstand any external damages or local defects. In this study, oil‐impregnated nanoporous anodic aluminum oxide (AAO) layers are investigated to overcome such limitations and thus advance corrosion protection. By completely filling hydrophobized nanopores with oil via a solvent exchange method, a highly water‐repellent surface that prevents the penetration of corrosive media into the AAO layer and hence the corrosion of aluminum is achieved. The impregnation of oil into the hydrophobic nanoporous AAO layer enhances the corrosion resistance of an AAO layer by two and four orders of magnitude compared to that of a hydrophobic (i.e., air‐entrained) and a bare (hydrophilic) AAO, respectively. In the presence of local defects, the oil impregnated within the hydrophobic nanoporous AAO layer naturally permeates into the defects and ultimately inhibits the exposure of the aluminum surface to corrosive media. Whereas the corrosion current density of the air‐entrained hydrophobic AAO layer increases by more than 30 times after cracks, that of the oil‐impregnated AAO layer increases by no more than 4 times, showing superior anticorrosion property even after there are cracks, owing to the effective self‐healing capability.

Wetting phenomena and superhydrophobic surfaces are ubiquitous in nature and have recently been explored widely in scientific and engineering applications. The understanding and control of surface superhydrophobicity are not only fundamentally intriguing but also practically important to provide unique and regulated functionalities to natural species and industrial applications. Here, the fundamentals of wetting phenomena are critically reviewed that especially apply to superhydrophobicity, putting an emphasis on the clarification of contact angles, the quantification of droplet retention force, and the role of contact line. The fundamentals of how the droplet retention is determined by the surface features are discussed and advanced analytical models for the prediction of contact angles and retentive forces are introduced. Applications are further discussed whose functionalities largely depend on the droplet retention, including directional droplet transport, anti‐icing, and water harvesting.

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Fog collection shows great promise as a solution to the water scarcity problem in some arid regions. In addition, it can be applied to saving water required for important industrial system processes, such as recapturing water in cooling towers of thermal power plants. Although a number of studies have been conducted to investigate the principles of fog collection, most of the studies have sought methods to facilitate the transport of the captured liquid on multiple wire systems. However, it is important to study the fundamental correlation between the fog collection rate and the process of fog droplet capture, which has been largely underexplored, in order to understand the full span of the fog collection process and improve its collection efficiency. In this study, we aim to examine the correlation between the measured collection rate and the deposition step of fog collection on a wire, using spontaneous wetting of vertical, superhydrophilic wires that minimize the liquid loss during transport to precisely measure the volume of collected water. Experiments were conducted using the wires with various diameters under different wind speed conditions. The results show that the measured fog collection rate per unit area is linearly proportional to an empirically obtained deposition efficiency of aerosols, a function of the Stokes number. In addition to the controlled liquid transport by the modification of surface wettability, this study provides physical insights for the optimal design of fog collectors from an aerodynamics-centered perspective, benefitting the fight against the global water crisis.

The time required to collect the initially deposited fog on a wire is determined by aerodynamics and interfacial phenomena.

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Surface tension and capillary forces were measured for water droplets in contact with anisotropic hydrophobic patterns made of microscopic ridges and grooves using a microbalance. Integrated with a charge-coupled device camera, the instrument allowed capturing of the synchronous images of a droplet during its spreading, compression, stretching and detachment. These images were used to analyze the evolution of the droplet shape and quantify its base diameter and contact angle in both the longitudinal and traverse directions. The experiments confirmed that a water droplet spreads preferentially along the longitudinal direction, on top of the ridges, following the continuity of the solid and producing asymmetry in the drop shape. Switching the droplet wetting mode from advancing to receding causes the droplet to symmetrize its shape. It was found that the maximum adhesion between the droplet and hydrophobic pattern coincides with droplet base circularity and apparent contact angles of nearly identical values measured in the longitudinal and traverse directions. These findings confirm that the most stable configuration for a liquid droplet on a rough solid surface appears only when the droplet base is axisymmetric. It is also demonstrated that the Cassie–Baxter equation pertains only to the droplet in the most stable state, where the excess free energy is minimized.

A microelectronic balance system was employed to measure the force of spreading (snap-in force) during water droplet attachment and spreading on polymer surfaces and the water-polymer adhesion forces (maximum adhesion and pulloff forces) after droplet compression, retreat and detachment. Equipped with a charge-coupled device camera and data acquisition software, the instrument measured directly the forces; monitored droplet-surface separation, including distances over which droplet stretched; and collected optical images simultaneously. The images were used to analyze capillary and surface tension forces based on measured droplet shape, surface curvature, droplet base radius and values of contact angles. The forces measured with the microbalance were compared to calculated capillary/surface tension forces. Nearly excellent agreement between directly measured and calculated forces was verified for polymers with smooth surfaces. Experiments with patterned polymers with pores and pillars revealed that interpretation of forces requires knowledge of a triple-contact-line characteristic. One relevant parameter, named normalized contact line length, was introduced to surface tension forces to quantify forces measured directly with a microbalance.