A superhydrophobic (SHB) surface with an excellent self-cleaning ability is of great significance in both human survival and industrial fields. However, it is still a challenge to achieve large-area preparation of antiabrasive SHB surfaces with great mechanical robustness for broader applications. Thus, a kind of facile SHB coating with excellent liquid repellency and antiresistance is constructed by spraying a fluorine-free suspension consisting of epoxy resin, hexadecyltrimethoxysilane (HDTMS), and silica nanoparticles on a glass sheet. The SHB coating not only shows high adhesion on various materials but also has high water repellency under various test conditions, including tape peeling after blade scraping, sandpaper abrasion, and immersing in a complex environment. Additionally, the SHB spheres coated with laser-induced microstructure armor could form a continuous gas cavity during the water entry process, which is essential to prolonging the drag reduction ability of SHB coatings in liquid. Finally, the prepared robust SHB coatings have been employed in underwater buoyancy enhancement and reducing fluid resistance, which may open new avenues for underwater drag reduction in the field of marine applications.
Shape memory polymers (SMPs) with tunable wettability and reversible adhesion through adjusting the surface morphology have great prospects in functional devices. However, current functional devices based on SMPs are mainly concentrated on the manipulation of diverse liquid droplets in the air; it is still a challenge to achieve the reversible tuning of underwater oil wettability and adhesion on the microstructured SMP surface. Herein, we fabricate a kind of SMP micropillar array through one-step femtosecond laser irradiation, which could achieve the reversible tuning of underwater oil wettability and adhesion between the tilted and upright states. It is worth noting that the deformed micropillar arrays show underwater oleophobicity and have a larger adhesion force to the oil droplet than that of upright micropillar arrays, which is mainly related to the variation of the contact area between the oil droplet and the micropillar array. Finally, we demonstrate the lossless oil droplet transfer underwater by using the micropillar array surface with different states. We believe the present work will bring some insights for researchers in the field of dynamically responsive tunable underwater oil droplet manipulation.
Numerous studies have focused on designing and fabricating functional interfaces that control movement behavior of underwater gas bubbles, which are ubiquitous in a variety of natural and industrial settings. Nevertheless, developing surfaces with in situ tunable bubble movement remain elusive because of current complicated tuning strategies on the specific materials. Inspired by natural pitcher plant and rice leaves, here we report a kind of slippery lubricant-infused anisotropic microgrooved surface (SLI-AMGS) fabricated by femtosecond laser direct writing technology and realize the in situ reversible switching between underwater bubble sliding and pinning by unidirectional mechanical tensile strain. Different experimental parameters including lubricant oil film thickness, bubble volumes and laser power have been researched to manifest the relationship with bubble sliding behaviors. The underlying mechanism of in situ reversible switching mainly lies on the decrease of the lubricant oil film thickness during the process of mechanical stretching in which the uniform and stable oil film layer becomes uneven. This uneven lubricant oil film results in an extraordinary increase of contact angle hysteresis and resistance. At last, we demonstrate a real-time dynamic modulation of the underwater bubble on the SLI-AMGS with a changing mechanical tensile strain for several repeatable times in different acid–based environments. Our work manifests great potential applications in widespread fields including underwater bubble microfluidics and microbubble robots.
The wear-resistant superhydrophobic (SHB) surfaces with excellent water-repellency ability were prepared by constructing a microtextured armor on an aluminum surface. With the assistance of laser-induced microtextures, the SHB surface could keep a longer water-repellency ability and a lower friction coefficient even after repeated friction tests under different loads and at different speeds. The mechanism of microtexture-protecting SHB coating is revealed based on both theoretical and elemental analysis. Additionally, we explore the relationship between the three-dimensional topography parameters (ISO 25178) and variation of water contact angles under different test recycles. The results show that the rough surface with appropriate S a and higher S ku exhibits a better wear resistance, which is mainly related to the storing ability of SHB coating inside the microtextures. Moreover, the surface with appropriate S tr exhibits excellent wear resistance, which is mainly associated with better chip-removal ability. Finally, the tribological properties of the microtextured SHB surface are researched. It is worth noting that compared with the microtextured surface without SHB coating and the SHB-coated surface without microtextures, the microtextured SHB surface has the lowest friction coefficient under dry friction because the SHB coating would largely decrease the surface energy of the interface, so the adhesion friction decreases. The microtexture armor on the surfaces would protect the wear of SHB coating, so the SHB coating inside the microtexture could continuously play the role of a particle lubricant at the sliding interface and decrease the friction force of the sliding interface. We believe that the present study would contribute to the further understanding of the constructing mechanism of anti-wear SHB surfaces and provide a new strategy for topography design of engineering surfaces with friction reduction properties.
Regulation over the generation of the Leidenfrost phenomenon in liquids is vitally important in a cutting fluid/tool system, with benefits ranging from optimizing the heat transfer efficiency to improving the machining performance. However, realizing the influence mechanism of liquid boiling at various temperatures still faces enormous challenges. Herein, we report a kind of microgrooved tool surface by laser ablation, which could obviously increase both the static and dynamic Leidenfrost point of cutting fluid by adjusting the surface roughness (Sa). The physical mechanism that delays the Leidenfrost effect is primarily due to the ability of the designed microgroove surface to store and release vapor during droplet boiling so that the heated surface requires higher temperatures to generate sufficient vapor to suspend the droplet. We also find six typical impact regimes of cutting fluid under various contact temperatures; it is worth noting that Sa has a great influence on the transform threshold among six impact regimes, and the likelihood that a droplet will enter the Leidenfrost regime decreases with increasing Sa. In addition, the synergistic effect of Sa and tool temperature on the droplet kinetics of cutting droplets is investigated, and the relationship between the maximum rebound height and the dynamic Leidenfrost point is correlated for the first time. Significantly, cooling experiments on the heated microgrooved surface are performed and demonstrate that it is effective to improve the heat dissipation ability of cutting fluid by delaying the Leidenfrost effect on the microgrooved heated surface.
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