Properties Of Superhydrophobic Surfaces Research Articles

Inhibition Effectiveness of Laser-Cleaned Nanostructured Aluminum Alloys to Sulfate-reducing Bacteria Based on Superwetting and Ultraslippery Surfaces.

This paper is a continued study on laser cleaning removal of marine microbiofouling from Al alloy surfaces. According to our previous study, it is noted that the antifouling functions of the generated laser-cleaned metallic surfaces must be highlighted. In this work, the inhibition effectiveness of the laser-cleaned Al alloy surfaces was evaluated using a type of vital marine microorganism, sulfate-reducing bacteria (SRB) Desulfovibrio desulfuricans subsp. desulfuricans, in a dynamic bacterial solution. Before the immersion tests, the laser-cleaned surfaces with nanostructures were chemically processed into superhydrophilic, superhydrophobic, and ultraslippery surfaces. SRB attachment behaviors as well as inhibition mechanisms of the three surfaces to the SRB settlement were characterized and revealed. The SRB adhering to the above surfaces presented three different morphologies, i.e., broken, dented, and plump cells. Superhydrophilic surfaces unexpectedly showed a not inferior antibacterial ability. A piercing effect of the nanostructures caused nontoxic mechanical damage to the cell membranes. The antiadhesion property of superhydrophobic solid-air hybrid surfaces was unreliable due to the loss of air bubbles. The morphology of the last surviving SRB cells left on the ultraslippery surfaces was basically plump. The stable repellent function of the surfaces was responsible for the vigorous prevention of the adhesion of the SRB. The research results offer an insight into the antibacterial/antiadhesion properties of the laser-cleaned surfaces and a practical value for the periodic service of marine high-end equipment.

The effect of the loss of superhydrophobic surface properties on biofouling and flow around shipbuilding's steel plates

The dependence of the degree of biofouling on the magnitude of the contact angle θ during temporary degradation of the superhydrophobic coating of shipbuilding steel A40S in the process of being under water is examined. The experiment showed that the gas gap between the liquid and the structured surface makes it difficult for the first settlements to appear at θ ≥ 130°. In 35 days of being underwater and losing the hydrophobic properties of the coating, there were discovered the serpules (Serpula vermicularis), bryozoans (Bryozoa) and green algae (Chlorophyta), but there is no balanus (Balanidae - Chthamalus stellatus) and sponges (Porifera), which are observed on the untreated opposite sample side. The results of an in vivo experiment were used to CFD the dependence of water's flow velocity along the plate surface. Numerical calculation was determined the ratio of the initial flow velocity rate to its value at the end of the model plates. The transition from the hydrophilic state to the hydrophobic state reduces the value of the surface resistance by 1.44 times (changes in the velocity ν0/ν ≈ 2.6 are hydrophilic, ν0/ν ≈ 1.8 hydrophobic). An increase in surface roughness due to fouling will further increase the speed ratio by another 1.19–1.22 times.

Excellent static and dynamic anti-icing properties of hierarchical structured ZnO superhydrophobic surface on Cu substrates

The anti-icing behavior of static and dynamic low-temperature droplets on the surface of microelectronic material was investigated. The ZnO-coated superhydrophobic surface (SPS), hydrophobic surface (HPS), hydrophilic surface (HS) and pure Cu surface were prepared by hydrothermal method and ultraviolet light irradiation. Under the static and dynamic anti-icing condition, the SPS had excellent anti-icing ability before −20 °C. Even if the temperature was −20 °C, the SPS still have longest delayed icing time when compared with other three surfaces. This work offers a theoretical guidance for anti-icing application of microelectronic materials.

The investigation of mechanical and thermal properties of super-hydrophobic nitinol surfaces fabricated by hybrid methods of laser irradiation and carbon ion implantation

Comparing with laser irradiation only, the laser ablation combined with chemical modification process is a widely used technique to obtain bio-inspired super-hydrophobic surface. However, the as-prepared surfaces may be polluted by toxic substance during chemical modification such as fluoroalkyl silane and stearic acid. The side effect of polluted functional surface on organisms and environment limited its application value. In this paper, a green and environmental-friendly super-hydrophobic surface was quickly fabricated on nitinol substrates through hybrid of nanosecond laser ablation and carbon ion implantation. The time that turning from super-hydrophilicity to super-hydrophobicity was only 16 h exhibiting high efficiency compared with pure laser processing. Surface morphology and chemical component were systematically investigated to reveal the formation mechanism of super-hydrophobicity in such short time. The mechanical abrasion tests implied that the mechanical properties of surface microstructure could be heightened after carbon ion implantation, showing the superior structure stability. It is noted that chemical modified super-hydrophobicity could be hardly destroyed under high temperature, and the thermal stability of this ion implanted super-hydrophobic surface was on a par with it. This hybrid method of laser irradiation and carbon ion implantation paves a green way for rapid fabrication super-hydrophobic surface on nitinol, which would have great application value in biomedicine and industry.

Mechanism analysis and durability evaluation of anti-icing property of superhydrophobic surface

In this study, numerical and experimental investigations were performed to analyse the anti-icing mechanism of superhydrophobic surface (SHS) and to evaluate the durability of anti-icing property of artificial SHS respectively. Firstly, by coupling the Level set-Volume of Fluid (CLSVOF) and solidification-melting model, a three-dimensional Computational Fluid Dynamics (CFD) model was proposed to track the morphological changes of droplets, as well to simulate the phase transition process. Then, the freezing process of single droplet on different wettability surfaces was simulated and compared. Results showed that the nucleation position inside the droplet was located at the center of the contact region between the droplet and cold surface. Meanwhile, the temperature change, thermal equilibrium state and solid–liquid interface in droplet during freezing were studied systematically. Furthermore, the freezing delay function of SHS was measured qualitatively and quantitatively by using the solidification/melting cloud and the variations in solid volume fraction, respectively, and the action mechanism on anti-icing properties of contact angle (CA) was revealed by the stable shape of droplet. On the basis of simulation, inspired by the clover leaf bionic concept, we obtained SHSs with anti-icing properties by double-discharge machining of high speed wire electrical discharge machining (HS-WEDM) and evaluated its durability through experiments. Results showed that the anti-icing properties of such surface had mechanical durability and long-term durability.

Wetting and tribological properties of superhydrophobic aluminum surfaces with different water adhesion

In this article, a facile and efficient nanosecond laser processing method was carried out to construct a grid of microgrooves on an aluminum surface. After modification with low surface energy materials, various superhydrophobic surfaces with different water adhesion are obtained. The wetting properties of the obtained samples could be regulated by adjusting the number and line spacing (LS) of laser processing steps. The contact angle of the obtained superhydrophobic samples increased with the decrease in LS, while the sliding angle showed the opposite trend. Increasing the number of laser processing steps is beneficial to increase the contact angle and reduce the sliding angle. The wetting mechanism was analyzed to explain the cause of change in the wetting behaviors. The tribological tests showed that the surface textures of superhydrophobic samples improved their tribological properties. What is more, whether it is under dry friction or water lubrication conditions, the obtained superhydrophobic samples with large LS have good anti-friction and wear-resistant ability. The advantages of the facile preparation and excellent tribological properties will definitely expand the use of laser-machined superhydrophobic surfaces.

Preparation and Properties of Superhydrophobic Surface of Conducting Polymer Based on Linking Reaction

Superhydrophobic Surfaces Have Great Application Value in the Fields of Self-Cleaning, Corrosion Resistance, Fluid Drag Reduction, Ice Resistance and the Like, While Superhydrophobic Surfaces with Transparency, Conductivity or Other Functions Have Larger Application Space. the Appearance of the Lotus Leaf Has a Self-Cleaning Function, and the Most Typical Example is the Lotus Leaf Surface Which is out of Silt But Not Imbrued. through the Research and Analysis of Superhydrophobic Phenomena in Nature, the Low Surface Energy Substances on Superhydrophobic Surfaces and the Micro-Nano Scale Hierarchical Structure Are Considered as the Two Decisive Factors for Forming Superhydrophobic. the Classical Theory of Surface Wettability Indicates That the Wettability of Liquid Depends on the Surface Energy and Surface Roughness. Various Methods Have Been Developed for the Preparation of Superhydrophobic Surfaces with Conducting Polymers. by Selecting Materials with Appropriate Surface Energy and Fine Control of Surface Structure, Various Surface Functionalization Can Be Realized.

Intermediate States of Wetting on Hierarchical Superhydrophobic Surfaces.

Wetting transition on superhydrophobic surfaces is commonly described as an abrupt jump between two stable states-either from Cassie to Wenzel for nonhierarchical surfaces or from Cassie to nano-Cassie on hierarchical surfaces. We here experimentally study the electrowetting of hierarchical superhydrophobic surfaces composed of multiple length scales by imaging the light reflections from the gas-liquid interface. We present the existence of a continuous set of intermediate states of wetting through which the gas-liquid interface transitions under a continuously increasing external forcing. This transition is partially reversible and is limited only by localized Cassie to Wenzel transitions at nanodefects in the structure. In addition, we show that even a surface containing many localized wetted regions can still exhibit extremely low contact angle hysteresis, thus remaining useful for many heat transfer and self-cleaning applications. Expanding the classical definition of the Cassie state in the context of hierarchical surfaces, from a single state to a continuum of metastable states ranging from the centimeter to the nanometer scale, is important for a better description of the slip properties of superhydrophobic surfaces and provides new considerations for their effective design.

Eco-friendly fabrication of superhydrophobic surface with anti-corrosion by transferring dendrite-like structures to aluminum substrate

The superhydrophobic surface was successful fabricated through spin-coating epoxy resin firstly and transferring the dendrite-like structures to aluminum substrate coated with epoxy resin. The combination of organic coating and superhydrophobic surface with dendritic micro-nano structures prevent the permeation of corrosive ions more effectively. The results indicated the fabricated superhydrophobic surfaces possessed a WCA and WSA of nearly 154° and 0°, exhibiting good superhydrophobicity. Besides, the superhydrophobic surface displayed an excellent repellency to acidic or alkaline droplets. The self-cleaning performance of the superhydrophobic surface against fine sand and chalk dust was also proved. Moreover, the anti-corrosion property of superhydrophobic surface has greatly improved due to the dual function of epoxy resin and the air pockets trapped in superhydrophobic surface. This eco-friendly and facile approach provides a novel strategy to prevent metal from corrosion, which will promote the application of superhydrophobic surface in metal protection field.

Anti-frosting/anti-icing property of nano-ZnO superhydrophobic surface on Al alloy prepared by radio frequency magnetron sputtering

Superhydrophobic (SHP) surfaces had promising application in anti-icing field. In this work, ZnO SHP surfaces were prepared on aluminum alloy by radio frequency (RF) magnetron sputtering. The structure, chemical composition, morphology, wettability of the SHP surfaces were investigated by using corresponding methods. The anti-frosting/anti-icing performance of the ZnO SHP surfaces were investigated. Morphology of surfaces showed that sputtering time affected the surface morphology of the ZnO surfaces. When the sputtering time was 15 min, the rough structure exhibited excellent anti-frosting/anti-icing property due to the exceptional superhydrophobicity and self-transfer behavior at subzero temperature, which composed by densely gathered nanoclusters. The freezing of water droplets was delayed for about 2 h, and frosting was delayed for approximately 5 h at the temperature of −10 °C. The SHP surfaces could efficiently enhance the anti-icing property in glaze ice. Meanwhile, the as-prepared ZnO SHP surfaces displayed a low ice-adhesion strength of 12 ± 4.7 kPa. However, the structure with large undulation and pore space reduced the anti-frosting/anti-icing property of the SHP surface. This work provided a direction for the design and preparation of anti-icing surfaces for power transmission lines.

The surface electrical analysis of Nano Polyurethane-Based Superamphiphobic composite insulation materials

In the early stage of this study, it was found that Polyurethane was only two ways to construct the super-hydrophobic surface. The second is to construct micro-nano structure with low surface energy materials. Specific preparation methods of superhydrophobic surfaces include heterogeneous nucleation method, plasma treatment method, etching method, sol-gel method, vapor deposition method, electrochemical method, alternating deposition method, template method, self-assembly method, solve-non-solvent method, direct film formation method, etc., and many successful examples have been achieved. The research work in this field is relatively few, and the materials involved are scattered. The research objectives are all focused on the construction of micro-nano multistage surface structures with low surface energy. At present, most of these works only test the corresponding electrical properties of superhydrophobic surfaces. In order to verify the application prospect of superhydrophobic surface in antifouling flashover, it is necessary to carry out in-depth research on its hydrophobic, fouling and discharge aspects.

Mapping micrometer-scale wetting properties of superhydrophobic surfaces

There is a huge interest in developing superrepellent surfaces for antifouling and heat-transfer applications. To characterize the wetting properties of such surfaces, the most common approach is to place a millimetric-sized droplet and measure its contact angles. The adhesion and friction forces can then be inferred indirectly using Furmidge's relation. While easy to implement, contact angle measurements are semiquantitative and cannot resolve wetting variations on a surface. Here, we attach a micrometric-sized droplet to an atomic force microscope cantilever to directly measure adhesion and friction forces with nanonewton force resolutions. We spatially map the micrometer-scale wetting properties of superhydrophobic surfaces and observe the time-resolved pinning-depinning dynamics as the droplet detaches from or moves across the surface.

Wetting Transition on Liquid-Repellent Surfaces Probed by Surface Force Measurements and Confocal Imaging.

Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.

Oil-Repellent and Corrosion Resistance Properties of Superhydrophobic and Superoleophobic Aluminum Alloy Surfaces Based on Nanosecond Laser-Textured Treatment

As two typical special wettability materials, superhydrophobic and superoleophobic surfaces are the most widely studied interfaces because of their excellent water-or oil-repellent ability. However, how to use a simple strategy to obtain those surfaces is still a huge challenge. On the other hand, corrosion tend to occur while using metallic materials, resulting in poor performance of metallic equipment and even serious safety hazards. In this work, a one-step strategy of nanosecond laser ablation was presented to construct the microstructures acquired by superhydrophobic and superoleophobic aluminum alloy surfaces. The superhydrophobic and superoleophobic properties of microstructured surfaces were obtained via high temperature and fluorosilane treatments on laser-processed surfaces, respectively, and the oil-repellent and corrosion resistance properties of both substrates were studied. The potentiodynamic polarization test shows that the superoleophobic surface had a better corrosion resistance than the superhydrophobic surface, which will provide an effective protection for the bare aluminum alloy. Meanwhile, the superoleophobic surface had good chemical stability. It is believed that the nanosecond laser technology can offer an effective strategy for constructing the microstructures acquired by large-area superhydrophobic and superoleophobic surfaces on aluminum alloy materials.

Lotus-Inspired Multiscale Superhydrophobic AA5083 Resisting Surface Contamination and Marine Corrosion Attack.

The massive and long-term service of 5083 aluminum alloy (AA5083) is restricted by several shortcomings in marine and industrial environments, such as proneness to localized corrosion attack, surface contamination, etc. Herein, we report a facile and cost-effective strategy to transform intrinsic hydrophilicity into water-repellent superhydrophobicity, combining fluorine-free chemisorption of a hydrophobic agent with etching texture. Dual-scale hierarchical structure, surface height relief and surface chemical elements were studied by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), successively. Detailed investigations of the wetting property, self-cleaning effect, NaCl-particle self-propelling, corrosion and long-term behavior of the consequent superhydrophobic AA5083 surface were carried out, demonstrating extremely low adhesivity and outstanding water-repellent, self-cleaning and corrosion-resisting performance with long-term stability. We believe that the low cost, scalable and fluorine-free transforming of metallic surface wettability into waterproof superhydrophobicity is a possible strategy towards anti-contamination and marine anti-corrosion.

Superhydrophobic poly(vinyl butyral) nanofibrous membrane containing various silica nanoparticles

Nanofibrous composite membranes were prepared by the elecrospinning process of poly(vinyl butyral) (PVB) solution that contained hydrophobic silica nanoparticles (SiO2). Various surface modifications of the silica nanoparticles have been used to improve the waterproofing capacity of the membrane. Specifically, investigation was made into the effects of the rheological properties of the solution, as well as on fibre diameter as exerted by the applied voltage and the tip-to-collector distance. It was found that drastically increasing shear viscosity and the elasticity of the solution with the silica nanoparticles demonstrated a negligible effect on the creation of nanofibres, an issue rarely discussed in the literature. In fact, increasing the applied voltage and the tip-to-collector distance resulted in heightening the average fibre diameter. According to water contact angle measurements, the given PVB nanofibrous membrane reinforced with the incorporated silica nanoparticles demonstrated superhydrophobic surface properties.

Oscillating Magnetic Drop: How to Grade Water-Repellent Surfaces

Evaluation of superhydrophobic (SH) surfaces based on contact angle measurements is challenging due to the high mobility of drops and the resolution limits of optical goniometry. For this reason, some alternatives to drop-shape methods have been proposed such as the damped-oscillatory motion of ferrofluid sessile drops produced by an external magnetic field. This approach provides information on surface friction (lateral/shear adhesion) from the kinetic energy dissipation of the drop. In this work, we used this method to compare the low adhesion of four commercial SH coatings (Neverwet, WX2100, Ultraever dry, Hydrobead) formed on glass substrates. As ferrofluid, we used a maghemite aqueous suspension (2% v/v) synthesized ad hoc. The rolling magnetic drop is used as a probe to explore shear solid–liquid adhesion. Additionally, drop energy dissipates due to velocity-dependent viscous stresses developed close to the solid–liquid interface. By fitting the damped harmonic oscillations, we estimated the decay time on each coating. The SH coatings were statistically different by using the mean damping time. The differences found between SH coatings could be ascribed to surface–drop adhesion (contact angle hysteresis and apparent contact area). By using this methodology, we were able to grade meaningfully the liquid-repelling properties of superhydrophobic surfaces.

Research of freezing kinetics of water drop on superhydrophobic coating surfaces

Introduction. Anti-icing coatings are used to prevent icing of the building roofs and power transmission line poles. One of the characteristics of anti-icing properties of superhydrophobic surfaces is the delay in the crystallization of drops on such surfaces. A significant delay in the crystallization of water drops on superhydrophobic substrates is noted in the scientific and technical literature. However, it is recorded in a number of papers that the delay time of crystallization on hydrophilic substrates is longer than the corresponding values on superhydrophobic surfaces. In connection with the foregoing, the study of the freezing kinetics of a water drop on a superhydrophobic surface in order to assess its efficiency is a relevant scientific and technical problem. Materials and methods. To evaluate the kinetics of freezing a of water drop on a superhydrophobic surface, the following experiment is conducted. A drop of water is placed on the superhydrophobic surface of the mortar substrate, which is placed in a freezer at a temperature of –18 °C. Studies of the drop freezing dynamics on the surface are performed using a Testo 875-1 thermal imager. To create a superhydrophobic surface, an aerosil R 972 with density ρ = 2360 kg/m3, particle size of 16 nm and specific surface area Ssp = 12 000 m2/kg is used as a filler. A silicone resin SILRES® MSE 100 of 10 % concentration is used as a binder. The obtained solutions are deposited on the mortar substrates. The degree of hydrophobicity is assessed by the magnitude of the wetting angle (θ°). Results. Results of the studies of temperature distribution on the water drop surface indicate that the distribution is uneven. The process of drop freezing is multistage. In the initial period, there is a transfer of heat from the surface into the water drop. This stage is followed by the process of drop freezing which is manifested in the upward movement of the freezing front from the substrate. Conclusions. It is revealed that the temperature distribution on the surface of a water drop is uneven. When freezing, a water drop has a pointed top.

Facile fabrication of a durable Ni3S2 nanorod arrays superhydrophobic surface with self-cleaning and degradation properties

Inspired by nature, the fabrication of superhydrophobic surface has aroused an extensive concern. In this work, a Ni3S2 superhydrophobic coating was achieved via the cooperation of solvothermal reaction and followed chemical modification. The coating surface showed a distinct repellence of water droplets, and the contact angle and sliding angle are 165° and 3°, respectively. The energy disperse spectrometer, X-ray diffractmeter and Fourier transform infrared spectroscopy were used to confirm the Ni3S2 superhydrophobic surface had been achieved by the solvothermal reaction and chemical modification. The morphology of the coating surface was observed by scanning electron microscope. It was found that Ni3S2 nanorod arrays were uniformly distributed on the surface. The superhydrophobic surface with an outstanding self-cleaning property could prevent the substrate from being polluted by different forms of contaminants. It was verified that Methylene blue molecules could be destroyed by Ni3S2 superhydrophobic coating. More importantly, a reversible conversion of superhydrophobicity and superhydrophilicity could be achieved on the coating surface. Furthermore, the as-prepared coating could withstand mechanical and chemical damages. These excellent properties of Ni3S2 superhydrophobic surface are favorable for the application in oil-water separation and corrosion protection.

Enhanced anti-icing and anti-corrosion properties of wear-resistant superhydrophobic surfaces based on Al alloys

We report herein on the preparation of a superhydrophobic surface by high-speed wire electrical discharge machining on the surface of a 7075 aluminium alloy without any chemical treatment. The morphology and the anti-icing, anti-wear and anti-corrosion properties of the superhydrophobic surface were characterised by scanning electron microscopy, contact angle measurements, a custom-made experimental apparatus, a universal mechanical tester and an electrochemical workstation, respectively. Our results indicated that the superhydrophobic specimen had a water contact angle of 154.3 ± 0.5°. The anti-icing, anti-corrosion and anti-wear properties of the prepared specimen were improved by approximately 70%, 110% and 160%, respectively. Moreover, the artificial surface could maintain its anti-icing properties even in the event of surface damage.