Loss Of Superhydrophobicity Research Articles

Anti-corrosion superhydrophobic micro-GF/micro-TiB2/nano-SiO2 based coating with braid strengthening structure fabricated by a single-step spray deposition

Superhydrophobic surfaces with self-cleaning, anti-biofouling and corrosion resistance merits are attractive for applications in major engineering fields. Generally, these surfaces possess low-surface-energy chemistry and micro- or nanoscale surface roughness. However, rough surfaces are fragile and highly susceptible to abrasion for high local pressures under mechanical load, causing loss of superhydrophobicity. In this study, we proposed a "fiber weaving/hard particles embedding-soft membrane" strategy to construct a kind of organic-inorganic composite coating by embedding micro-glass fiber (GF)/micro-TiB2/nano-SiO2 particles into the polydimethylsiloxane (PDMS)@polyurethane (PU) for fabricating robust superhydrophobic coating. The addition of micro-nano ceramic particles plays two roles including "hard" micro-skeletons to overcome vulnerable issue of "soft" organic membrane and creation of wear-resistant bearing points on the surface. Furthermore, "soft" membrane can absorb stress when subjected to external mechanical force and PU serves as an adhesive to improve interfacial bond strength. Additionally, GF intersperses in the coating, providing anchoring effect and PDMS serves as a modifier to decrease surface energy. Consequently, the proposed hybrid coating could simultaneously augment its mechanical robustness and multifunctional performance, breaking the notorious "trade-off" restriction of superhydrophobic coating. The preparation parameters and operation condition on the performance of the coating were investigated systematacially. The optimized superhydrophobic coating exhibits the highest water contact angle (WCA) of 167.3° ± 3.9°, the lowest sliding angle (SA) of 4.6° ± 1.3°, corrosion protection efficiency of 95.7 % in 3.5 wt% NaCl solution, with exceptional self-cleaning, anti-pollution, adaptability to various substrates, thermostable, anti-icing and mechanical stability properties, among the top-tier multifunctional performance. The inherent properties of micro-glass fiber, micro-TiB2 and nano-SiO2 ceramics and their highly ordered arrangement in the superhydrophobic coating are expected to provide an effective and versatile design proposal for potential applications in corrosion protection.

Durability and Additional Properties of Anodized Aluminum-Based Coatings with Different Wettability under Natural Conditions.

The study aimed to test the durability of coatings under natural conditions. The present study focused on the changes in wettability and additional properties of the coatings under natural conditions. The specimens were subjected to outdoor exposure and additionally immersed in the pond. Impregnating porous anodized aluminum is a popular production method for hydrophobic and superhydrophobic surfaces. However, prolonged exposure of such coatings to natural conditions causes leaching of the impregnate and, thus, the loss of hydrophobic properties. After the loss of hydrophobic properties, all kinds of impurities and fouling adhere better to the porous structure. Additionally, deterioration of anti-icing and anti-corrosion properties was observed. Finally, the self-cleaning, anti-fouling, anti-icing and anti-corrosion properties were comparable or even worse to those of the hydrophilic coating. In the case of superhydrophobic specimens, during outdoor exposure there was no loss of superhydrophobicity, self-cleaning and anti-corrosion properties. Still, despite this, the icing delay time dropped. During outdoor exposure, the structure, which initially had anti-icing properties, may degrade. Nevertheless, the hierarchical structure responsible for the superhydrophobic effect can still be preserved. The superhydrophobic coating initially had the best anti-fouling properties. However, the coating was also gradually losing its superhydrophobic properties during water immersion.

Nanosecond laser fabrication of superhydrophobic copper and anti-frost surface on copper

The frost phenomenon on metal surfaces seriously reduces the system operation efficiency, and the research of robust and effective waterproof protective layer on metal surfaces has become a focus of attention. The ability of superhydrophobic surfaces to stay dry is attractive for frost suppression performance on metal surfaces. However, when subjected to external pressure, the waterproof protective layer is highly susceptible to damage, resulting in the loss of superhydrophobicity. Therefore, a copper surface possessing superhydrophobicity and mechanical robustness was designed and fabricated in this study. The design of robust micro-nano structures on copper surfaces using finite element analysis. The combined modification of the copper surface using nanosecond laser and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES). Or refilled nano-silica to form the combined surface. The contact angle of the combined surface was 160.3°, and the rolling angle was 1°, both of which helped to obtain superhydrophobicity. The mechanical robustness of the superhydrophobic copper surface was tested by knife, stainless steel wire ball, and tape. The freezing and anti-freezing properties of the droplet on the superhydrophobic copper surface and ordinary copper surface were observed by experiments. The results show that the surface of superhydrophobic copper still keeps superhydrophobicity after repeated mechanical durability tests. When the frost thickness is 0.9 mm (cooling temperature of −7 °C, horizontal placement), the superhydrophobic copper surface (composite surface) has excellent frost suppression performance compared to the ordinary copper surface, and the growth of frost could be delayed by 1.75 times. Meanwhile, the hydrophobicity of the superhydrophobic copper surface remained essentially unchanged after 50 freeze-thaw cycle experiments (a single cooling time of 30 min). We believe that the practical aspects of anti-frost design strategies on the copper surface show a great advantage.

Droplet Dynamics and Freezing Delay on Nanoporous Microstructured Surfaces at Condensing Environment

Superhydrophobic surfaces have aroused great interest for being promising candidates in applications such as self-cleaning, anti-icing, and corrosion resistance. However, most of the superhydrophobic surfaces lose their anti-wettability in low surface temperature and high humidity. The loss of superhydrophobicity by condensed liquid is a very common practical incident, yet to be understood properly. Here we report the wettability of the superhydrophobic nanoporous surfaces in condensation and freezing environments. Various structured surfaces fabricated with carbon nanotubes (CNT) and coated by an ultrathin, conformal, and low surface energy layer of poly (1H,1H,2H,2H-perfluorodecylacrylate) (pPFDA) are exploited in humid conditions. Droplet impact dynamics, condensate characteristics, and freezing time delays are investigated on the CNT micropillars with various geometries along with the CNT forest and two commercially available anti-wetting coatings, NeverWet and WX2100. Nanoporous microstructured CNT pillars with the favorable topological configuration demonstrated complete droplet bouncing, significant freezing delays, and considerable durability during several icing/de-icing cycles. This study provides an understanding on the preferable geometry of the highly porous CNT micropillars for retaining hydrophobicity and preventing ice formation, which is of practical importance for the rational development of anti-wetting surfaces and their applications in low temperatures and humid conditions.

Robust Self‐Cleaning and Marine Anticorrosion Super‐Hydrophobic Co–Ni/CeO2 Composite Coatings

Until now, superhydrophobic materials that are scale‐up fabrication and application to harsh environments remain challenging because of their fragile mechanical durability. Because of their unique electronic structure, rare‐earth oxides (REOs) have been proven to be intrinsically hydrophobic. Herein, cerium oxide particles (CeO2) are added to the coating by coelectrodeposition. The Co–Ni/CeO2 composite coating from the electrolyte containing 3.44 g L−1 possesses a flower‐like hierarchical structure, displaying a superhydrophobic behavior after the modification by 1H,1H,2H,2H‐perfluorooctyltrichlorosilane (PFTEOS). More importantly, excellent mechanical durability with critical abrasion distance of 22.5 m is achieved under a 5 kPa fixed normal pressure in the liner abrasion test before the loss of superhydrophobicity. Also, electrochemical measurements demonstrate that the superhydrophobic composite coatings display high corrosion resistance.

Fabrication of coral-reef structured nano silica for self-cleaning and super-hydrophobic textile applications

Non wettable surfaces have attracted attention for their promising potential in anti-fouling and self-cleaning applications. However, the complex fabrication and loss of super-hydrophobicity because of poor durability have restricted their commercial applications. To address these issues, a robust super-hydrophobic surface was fabricated through construction of a coral-reef like fibrous structure, followed by adhesive-assisted dip coating. Wrinkled fibrous nano silica (WFNS) was synthesized using the Winsor III system. WFNS having hierarchal surface and enhanced surface area was modified by salinizing agent and by coated on various substrates. This fibrous structure aids to minimize the water/solid interface resulted to achieve the super-hydrophobic surface with a water contact angle of 167°. To impart mechanical and chemical robustness, an adhesive-assisted approach was used. The as-prepared surface maintained a remarkable super-hydrophobicity even after mechanical and chemical stresses. The prepared super-hydrophobic surface illustrated excellent anti-fouling performance against corrosive liquids and an antimycotic property. The combination of liquid repellency and exceptional robustness exhibited indicates the WFNS as a promising candidate for super-hydrophobic and self-cleaning applications.

Thermally-induced all-damage-healable superhydrophobic surface with photocatalytic performance from hierarchical BiOCl

Preparation of superhydrophobic surfaces capable of recovering both the surface chemistry and hierarchical structure is still a challenge. In this work, all-damage-healable superhydrophobic surface was fabricated by assembly of superhydrophobic and hierarchical BiOCl on lignocellulosic substrates. Fibers having thermally responsive behavior, the main component of lignocellulosic materials, act as the underlying movable substrates. By a simple heating treatment, fibers can convey the undamaged neighbored superhydrophobic coating to the damaged area. In this way, the loss of superhydrophobicity caused by rigorous mechanical destructions, even deep cuts of one hundred of micrometers wide, can be restored, mimicking the self-healing mechanism of human skin. Superior self-healing ability in surface chemistry was also confirmed. Meanwhile, the as-prepared superhydrophobic surfaces demonstrated reliable photocatalytic ability, a useful property for resisting organic contaminations. Interestingly, it was found that the photocatalytic activity can be enhanced by tuning the surface wettability. This work reported the first use of substrate material’s inherently thermally responsive property to demonstrate self-healing superhydrophobic surface with photocatalyticity, which not only promotes the application of superhydrophobic materials in complex environment, but also opens up a new perspective in designing durable superhydrophobic materials.

UV-Resistant and Thermally Stable Superhydrophobic CeO2 Nanotubes with High Water Adhesion.

A novel type of sticky superhydrophobic cerium dioxide (CeO2 ) nanotube material is prepared by hydrothermal treatment without any chemical modification. A water droplet on the material surface shows a static water contact angle of about 157° but the water droplet is pinned on the material surface even when the material surface is turned upside down. Interestingly, the as-prepared CeO2 nanotube material displays durable superhydrophobicity and enhanced adhesion to water under ultraviolet (UV) light irradiation. Importantly, this change in water adhesion can be reversed by heat treatment to restore the original adhesive value of 20 µL. Further, the maximum volume of the water droplet adhered on the material surface of CeO2 nanotubes can be regulated without loss of superhydrophobicity during the heating treatment/UV-irradiation cycling. Meanwhile, the superhydrophobic CeO2 nanotube material shows remarkable thermal stability even at temperatures as high as 450 °C, long-term durability in chemical environment, and air-storage and good resistance to oily contaminant. Finally, the potential application in no-loss water transportation of this sticky superhydrophobic CeO2 material is demonstrated.

Robust Superhydrophobic Laser‐Induced Graphene for Desalination Applications

AbstractThe fabrication of long‐lived, durable, superhydrophobic surfaces using a manufacturable process is an important challenge for material science. Significant advances have been reported; however, many surfaces suffer from fragility, nonmanufacturable fabrication techniques, and temporal instability. Such challenges have limited commercial scale application of superhydrophobic films, including their application to water desalination where long lifetimes and durability are essential. The fabrication of controllably wettable surfaces formed from laser‐induced graphene is demonstrated in atmospheric conditions with contact angle control from 59° to 176°; representing some of the most superhydrophobic carbon surfaces ever reported. This superhydrophobicity is used to engineer a membrane with the largest pores ever reported for the energy efficient water desalination technique of air‐gapped membrane distillation. State‐of‐the‐art production of distilled water is observed, and no membrane failure or loss of superhydrophobicity is observed on a time‐scale of months—suggesting total water production capabilities well beyond anything yet demonstrated.

Wetting Transition of Condensed Droplets on Nanostructured Superhydrophobic Surfaces: Coordination of Surface Properties and Condensing Conditions.

Nanostructured superhydrophobic surfaces have been actively explored to promote favorable droplet dynamics for a wide range of technological applications. However, the tendency of condensed droplets to form as pinned states greatly limits their applicability in enhancing condensation heat transfer efficiency. Despite recent progresses, the understanding of physical mechanisms governing the wetting transition of condensed droplets is still lacking. In this work, a nanostructured superhydrophobic surface with tapered nanogaps is fabricated to demonstrate the coordination of surface wetting property, topography, and the condensing condition on the wetting state and dynamic behavior of condensed droplets. Combining the environmental scanning electron microscopy and optical visualization methods, we systematically show the morphology of nucleated droplets in nanostructures and the droplet dynamic evolution throughout the growth stages, which provides the direct evidence of condensing condition-induced droplet wetting transition. When the surface subcooling is smaller than 0.3 K, the droplets formed as the Cassie-Baxter state, followed by coalescence-induced droplet jumping. With the increase of surface subcooling up to 0.6 K, however, droplet formation occurs randomly inside nanogaps, resulting in the loss of superhydrophobicity. These new observations along with the new insights about the coordination of surface properties and condensing conditions on droplet wetting transition are useful for guiding the development of novel surfaces for improving droplet removal and phase-change heat transfer.

Facile fabrication of superhydrophobic conductive graphite nanoplatelet/vapor-grown carbon fiber/polypropylene composite coatings

Abstract The fabrication of superhydrophobic surfaces with mechanical durability is challenging because the surface microstructure is easily damaged. Herein, we report superhydrophobic conductive graphite nanoplatelet (GNP)/vapor-grown carbon fiber (VGCF)/polypropylene (PP) composite coatings with mechanical durability by a hot-pressing method. The as-prepared GNP/VGCF/PP composite coatings showed water contact angle (WCA) above 150° and sliding angle (SA) less than 5°. The superhydrophobicity was improved with the increase of VGCF content in the hybrid GNP and VGCF fillers. The more VGCFs added in the GNP/VGCF/PP composite coating, the higher porosity on the surface was formed. Compared to the GNP/PP and VGCF/PP composite coatings, the GNP and VGCF hybrid fillers exhibited more remarkable synergistic effect on the electrical conductivity of the GNP/VGCF/PP composite coatings. The GNP/VGCF/PP composite coating with GNP:VGCF = 2:1 possessed a sheet resistance of 1 Ω/sq. After abrasion test, the rough microstructure of the GNP/VGCF/PP (2:1) composite coating was mostly restored and the composite coating retained superhydrophobicity, but not for the VGCF/PP composite coating. When the superhydrophobic surface is mechanically damaged with a loss of superhydrophobicity, it can be easily repaired by a simple way with adhesive tapes. Moreover, the oil-fouled composite surface can regenerate superhydrophobicity by wetting the surface with alcohol and subsequently burning off alcohol.

Is superhydrophobicity robust with respect to disorder?

We consider theoretically the Cassie-Baxter and Wenzel states describing the wetting contact angles for rough substrates. More precisely, we consider different types of periodic geometries such as square protrusions and disks in 2D, grooves and nanoparticles in 3D and derive explicitly the contact angle formulas. We also show how to introduce the concept of surface disorder within the problem and, inspired by biomimetism, study its effect on superhydrophobicity. Our results, quite generally, prove that introducing disorder, at fixed given roughness, will lower the contact angle: a disordered substrate will have a lower contact angle than a corresponding periodic substrate. We also show that there are some choices of disorder for which the loss of superhydrophobicity can be made small, making superhydrophobicity robust.

Restoration of Superhydrophobicity in Crushed Polymer Films by Treatment with Water: Self‐Healing and Recovery of Damaged Topographic Features Aided by an Unlikely Source

The crushing of superhydrophobic polymer multilayers destroys micro/nanoscale topographic features critical for the maintenance of superhydrophobicity. We demonstrate that these surface features can be recovered, and that superhydrophobicity can be fully restored, by treatment of damaged films with liquid water. These polymer-based films can also sustain other forms of severe abuse without loss of superhydrophobicity. This combination of features addresses several important practical issues associated with the durability of artificial superhydrophobic surfaces.

Water condensation on superhydrophobic aluminum surfaces with different low-surface-energy coatings

In this work, we have fabricated superhydrophobic aluminum surfaces by a facile chemical etching method. Surface morphology and composition were studied by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). To comparatively investigate the effect of environmental factors on superhydrophobic behaviors of surfaces with different low-surface-energy coatings under controllable condensation conditions, contact and sliding angles were measured from −10°C to 30°C under relative humidity (RH) of 30, 60 and 90%, respectively. The calculation of the solid–liquid contact area fraction quantitatively explained the increased wettability characterized by descending contact angle and ascending sliding angle under low temperature and high humidity, and indicated a transition of the equilibrium state from Cassie–Baxter to Wenzel on rough surfaces. The wettability restoration test showed that the loss of superhydrophobicity during condensation could be recovered completely after a drying process at room temperature.

Compressed Metal Powders that Remain Superhydrophobic after Abrasion

Superhydrophobic “lotus effect” materials are typically not sufficiently robust for most real world applications because their small surface features are both easily damaged and vulnerable to fouling. Here, a method for preparing a new type of superhydrophobic (θ > 162°) composite material by compression of superhydrophobic metal particles is reported. This material, which has no natural analogue, has low-surface-energy microstructures extending throughout its whole volume. Removing its outer layer by abrasion or cutting deep into it does not result in loss of superhydrophobicity because it merely exposes a fresh portion of the underlying superhydrophobic material. The high contact angle is therefore retained even after accidental damage, and vigorous abrasion can be used to restore hydrophobicity after fouling.