Recent progress in superhydrophobic coating on Mg alloys:A general review

Magnesium(Mg)is a vital engineering material owing to its light weight and excellent mechanical properties.However,poor corrosion resistance limits its widely applications as well as its economic value.Hence,surface modification is essential for Mg and its alloys.Among the various coatings,superhydrophobic coating,which is inspired by nature,has received increasing attentions in the past decade.With a water contact angle larger than 150°,superhydrophobic coating can provide sufficient protection for Mg-based substrates.The model of superhydrophobic states and the protection mechanism of superhydrophobic coating are discussed in this review.Especially,the methods for fabricating superhydrophobic coatings on Mg alloys are reviewed.Meanwhile,some functional superhydrophobic coatings on Mg alloys are summarized.Finally,the challenges and future directions are proposed.We hope that this paper will provide a serviceable review for future research on superhydrophobic coatings on Mg alloys.

EDTA interfacial chelation Ca^(2+) incorporates superhydrophobic coating for scaling inhibition of CaCO_(3) in petroleum industry

In this paper,the superhydrophobic poly(vinylidene fuoride)/fuorinated ethylene propylene/SiO_(2)/CNTs-EDTA(PFSCEDTA)composite coating was successfully fabricated and applied for anti-scaling performance.The deposition of CaCO_(3) on the surface of the superhydrophobic PFSC-EDTA composite coating reached 0.0444 mg/cm^(2) for 192-h immersion into the supersaturated CaCO_(3) solution,which was only 11.4%that of the superhydrophobic PFSC composite coating.At the interface between the CaCO_(3) solution and the PFSC-EDTA coating,the Ca^(2+)could be frstly chelated by EDTA that was beneft for improving the anti-scaling performance of the superhydrophobic PFSC-EDTA composite coating.In another hand,the addition of EDTA to the CNTs played an important role in fabricating the SiO_(2)-centric and CNTs-EDTA-surrounded multilevel micro-nanostructure in the superhydrophobic PFSC-EDTA composite coating,in favor of maintaining the air flm under the water and the stability of the superhydrophobic surface.The research supplies a new way of improving antiscaling performance of superhydrophobic coating by incorporating the organic chelating agent at the interface and changing the traditional way of scale prevention.

A route for large-scale preparation of multifunctional superhydrophobic coating with electrochemically-modified kaolin for efficient corrosion protection of magnesium alloys

Superhydrophobic coating has been widely studied for its great applicational potential, such as for corrosion protection of magnesium alloys while it has been restrained by expensive materials, sophisticated preparation process and infirm rough structures. In this study, the electrochemical method was adopted by using a two-electrode system for rapid hydrophobic modification to obtain superhydrophobic kaolin.By mixing the modified superhydrophobic kaolin with commercial epoxy resin and polydimethylsiloxane glue, a paint can be formed and easily used on various substrates for preparation of superhydrophobic coating via spraying method. The influence factors on wettability of the modified kaolin and the mixing ratio of each component of the coating were explored. Also, the wettability, durability and anticorrosion of the prepared coating were evaluated comprehensively. The coating was able to maintain superhydrophobic after immersed in HCl solution at pH 1, the NaOH solution at pH 14, and 3.5 wt.% NaCl solution for 16, 21, 30 days, respectively. In addition, the coating exhibited 4A grade adhesion, high hydrophobicity after abraded for 200 cycles on a 600-mesh sandpaper with 100 g weight, and 99.86% anticorrosion efficiency after soaked in 3.5 wt.% NaCl solution for 20 days, demonstrating a good robustness and anti-corrosion property. Furthermore, the coating showed good transparency, flexibility and was easy to make in a large scale by the spraying method, which is of great significance to promote the practical application of superhydrophobic coatings and the anticorrosion Mg alloys.

Superhydrophobic Coating Fabrication for Metal Protection Based on Electrodeposition Application: A Review

In recent years, superhydrophobic media has attracted tremendous attention due to its industrial applicability value, especially in anti-corrosion performance. The superhydrophobic coating, which has a robust and water-repellent capacity, can catch the air to form several “airbags” on the substrate’s surface, isolating the corrosion media. Various superhydrophobic coating preparation technologies have been suggested, but each has its own set of flaws. On the other hand, electrodeposition, as a relatively mature industrial processing application, offers distinct advantages. However, until now, there have been few reviews on the electrodeposition preparation of anticorrosive superhydrophobic coatings. Therefore, the author has described several fabrication techniques based on superhydrophobic coatings in this review, including the advantages and disadvantages. Superhydrophobic coatings conventional concepts and wettability, as well as the model wetting concepts, have been reviewed. The coating processing status and the corrosion-resistant potential through the electrodeposition of metal and comparable composite are detailly encapsulated. Furthermore, electrodeposition parameters, including current density, crystal modifiers, and a deposition time of the coating morphology, are reported, following the ultrasonic-assisted, jet, pulse, and magnetic field-induced electrodeposition, respectively, as the recently developed technologies for preparing a coating. Finally, technology limitation is shown as well as the obstacles and prospects, and the improvement of the superhydrophobic coating’s durability as a prospects research focus has been recommended.

Superhydrophobic coatings for corrosion protection of magnesium alloys

Magnesium(Mg)alloys show great potential to be extensively applied in practice owing to their superior properties,while the poor corrosion resistance does undoubtedly restrict their applications.Superhydrophobic coatings with good repellency to corrosive solutions can significantly decrease the interaction between the corrosive species and the substrate,so that they are receiving a lot of attention to improve the corrosion resistance of Mg alloys.Various strategies have been introduced to develop a superhydrophobic coating on Mg alloys,which were reviewed to elucidate the current research status to provide a clue or thinking for beginning researchers.Further,the existing issues of superhydrophobic coating were discussed,especially for their real applications in practice,mainly owing to their poor mechanical stability.Based on the existing issues,the future study was discussed to improve the stability of hierarchical structures and entrapped air pockets,impart the superhydrophobic coating self-healing property to repair the damaged area during service,provide double protection by incorporation of corrosion inhibitors,or even introduce slippery liquid-infused porous surfaces with lubricant layer to provide better corrosion protection for Mg alloys.

Superhydrophobic and mechanically robust polysiloxane composite coatings containing modified silica nanoparticles and PS-grafted halloysite nanotubes

Excellent mechanical properties are the prerequisite for the application of superhydrophobic polymer coatings.However,significantly improving the mechanical properties without affecting other properties such as hydrophobicity is a huge challenge.In this study,a superhydrophobic coating with excellent mechanical properties was prepared by spraying a mixture of polysiloxane resins based on three siloxane monomers,hexadecyltrimethoxysilane(HDTMS) modified nano-SiO_(2)particles(SiO_(2)-HDTMS) and polystyrene-grafted halloysite nanotubes(HNTs-PS).SiO_(2)-HDTMS dispersed homogeneously in polysiloxane coatings and the water contact angle of corresponding coating exceeding 150°,achieving superhydrophobicity.The SiO_(2)-HDTMS/HNTs-PS/polysiloxane composite coatings showed excellent abrasion resistance with the water coating contact angle remaining above 150°after 90 abrasion cycles,indicating that HNTs-PS can significantly improve the mechanical properties of the coating without affecting the hydrophobic properties of the coating.The achieved coating also exhibited excellent antifouling and acid and alkali corrosion resistance.This work provides a convenient and ecologically friendly method to prepare superhydrophobic polysiloxane composite coating with excellent mechanical properties,which is promising in the application of anti-fouling,anti-corrosion,and oil-water separation etc.

Hydroxyapatite/palmitic acid superhydrophobic composite coating on AZ31 magnesium alloy with both corrosion resistance and bacterial inhibition

The coating-modified magnesium(Mg)alloys exhibit controllable corrosion resistance,but the insufficient antibacterial performance limits their clinical applications as degradable implants.Superhydrophobic coatings show excellent performance in terms of both corrosion resistance and inhibition of bacterial adhesion and growth.In this work,a hydroxyapatite(HA)/palmitic acid(PA)superhydrophobic composite coating was fabricated on the Mg alloy by the hydrothermal technique and immersion treatment.The HA/PA composite coating showed superhydrophobicity with a contact angle of 153°and a sliding angle of 2°.The coated Mg alloy exhibited excellent corrosion resistance in the simulated body fluid,with high polarization resistance(77.10 kΩ·cm^(2))and low corrosion current density((0.491±0.015)μA·cm^(-2)).Meanwhile,the antibacterial efficiency of the composite coating was over 98% against E.coli and S.aureus in different periods.The results indicate that the construction of such superhydrophobic composite coating(HA/PA)on the Mg alloy can greatly improve the corrosion resistance of Mg alloy implants within the human body and avoid bacterial infection during the initial stages of implantation.

Near‑Instantaneously Self‑Healing Coating toward Stable and Durable Electromagnetic Interference Shielding

Durable electromagnetic interference(EMI)shielding is highly desired,as electromagnetic pollution is a great concern for electronics’stable performance and human health.Although a superhydrophobic surface can extend the service lifespan of EMI shielding materials,degradation of its protection capability and insufficient self-healing are troublesome issues due to unavoidable physical/chemical damages under long-term application conditions.Here,we report,for the first time,an instantaneously self-healing approach via microwave heating to achieve durable shielding performance.First,a hydrophobic 1H,1H,2H,2H-perfluorooctyltriethoxysilane(POTS)layer was coated on a polypyrrole(PPy)-modified fabric(PPy@POTS),enabling protection against the invasion of water,salt solution,and corrosive acidic and basic solutions.Moreover,after being damaged,the POTS layer can,for the first time,be instantaneously self-healed via microwave heating for a very short time,i.e.,4 s,benefiting from the intense thermal energy generated by PPy under electromagnetic wave radiation.This self-healing ability is also repeatable even after intentionally severe plasma etching,which highlights the great potential to achieve robust and durable EMI shielding applications.Significantly,this approach can be extended to other EMI shielding materials where heat is a triggering stimulus for healing thin protection layers.We envision that this work could provide insights into fabricating EMI shielding materials with durable performance for portable and wearable devices,as well as for human health care.

Durable Design of Superhydrophobic Coatings with TiO_(2)Particles and Al_(2)O_(3)Whiskers for the Enhanced Anti-icing Performance

Superhydrophobic coatings with high non-wetting properties are widely applied in anti-icing applications.However,the micro-nanostructures on the surfaces of superhydrophobic coatings are fragile under external forces,resulting in reduced durability.Therefore,mechanical strength and durability play a crucial role in the utilization of superhydrophobic materials.In this study,we employed a two-step spraying method to fabricate superhydrophobic FEVE-based coatings with exceptional mechanical durability,utilizing fluorinated TiO_(2)nanoparticles and fluorinated Al_(2)O_(3)microwhiskers as the fillers.The composite coating exhibited commendable non-wetting properties,displaying a contact angle of 164.84°and a sliding angle of 4.3°.On this basis,the stability of coatings was significantly improved due to the interlocking effect of Al_(2)O_(3)whiskers.After 500 tape peeling cycles,500 sandpaper abrasion tests,and 50 kg falling sand impact tests,the coatings retained superhydrophobicity,exhibiting excellent durability and application capability.Notably,the ice adhesion strength on the coatings was measured at only 65.4 kPa,while the icing delay time reached 271.8 s at-15℃.In addition,throughout 500 freezing/melting cycles,statistical analysis revealed that the superhydrophobic coatings exhibited a freezing initiation temperature as low as-17.25℃.

Protective and water-repellent properties of alkylcarboxylic and alkylphosphonic acid films on technically pure magnesium

The formation of superhydrophobic coatings using low-toxicity corrosion inhibitors is a promising method for corrosion protection of metals and alloys. In this study, the effects of surface roughness and the of the adsorbed substance structure on wettability and corrosion resistance of commercially pure magnesium were investigated. Surface roughness was created by three different methods: paper grinding,etching in nitric acid solution and laser treatment. Oleic, stearic and octadecylphosphonic acids were investigated as potential surface modifiers for the formation of corrosion resistant superhydrophobic coatings. It has been shown that the protective and hydrophobic properties of acid films on magnesium, as well as their stability, are determined by both the initial surface morphology and the nature of the inhibitors.Experimentally, the laser treatment was found to be preferable to mechanical and chemical surface preparation and the best hydrophobic agent among the studied acids is phosphonic acid. The most stable films with excellent superhydrophobic and protective properties in atmospheres of high humidity and salt spray clamber are formed in a solution of 0.001 M octadecylphosphonic acid on the surface of magnesium with high roughness. In addition, the effect of vinyltrimethoxysilane on the protective and hydrophobic properties of stearic acid and octadecylphosphonic acid films was investigated. The results of direct corrosion tests and wetting contact angle degradation kinetics studies showed that the protective and hydrophobic properties of stearic acid can be enhanced by its layer-by-layer adsorption with silane.They practically reach the parameters of octadecylphosphonic acid.

A Simple Method for Fabrication of Bionic Superhydrophobic Zinc Coating with Crater-like Structures on Steel Substrate

Surface modification with superhydrophobicity is a popular and challenging research field on metals. In this work, a simple method was used to fabricate a bionic superhydrophobic zinc coating with crater-like structures on pipeline steel surface. This method involved electrodeposition of zinc coating and chemical reaction in perfluorooctanoic acid ethanol solution. The per- fluorooctanoic acid with low surface free energy was not only used for chemical etching but also used for fluorinated modifi- cation. The contact angle of water on such superhydrophobic zinc coating was up to 154.21°, and the sliding angle was less than 5° due to the micro crater-like structures and the low surface free energy. Moreover, the prepared superhydrophobic zinc coating demonstrated excellent self-cleaning property and great stability at room temperature, and the contact angle of water on this coating remained stable after storage in air for more than 80 days. This superhydrophobic zinc coating will open much wider applications of electrodeposition metal coating, including self-cleaning property, and can be easily extended to other metals.

Corrosion resistance of a superhydrophobic micro-arc oxidation coating on Mg-4Li-1Ca alloy

A micro-arc oxidation（MAO）/zinc stearate（ZnSA） composite coating was fabricated via MAO processing and subsequent sealing with electrodeposition of a superhydrophobic ZnSA. The surface morphologies,chemical composition and corrosion resistance of the coatings were investigated using field-emission scanning electron microscopy, Fourier transform infrared, X-ray diffraction and electrochemical and hydrogen evolution measurements. Results indicated that the MAO coating was efficiently sealed by the following superhydrophobic ZnSA coating. The MAO/ZnSA composite coating significantly enhanced the corrosion resistance of Mg alloy Mg-4 Li-1 Ca due to its superhydrophobic function. Additionally, corrosion mechanism was suggested and discussed for the composite coating.

Green Synthesis of Mechanical Robust Superhydrophobic CNT@PU Coatings with High Flexibility for Extensive Applications

Superhydrophobic coatings with high flexibility and mechanical durability can well address many practical application problems.To this end,we proposed and fabricated a kind of bio-based superhydrophobic(multi-walled carbon nanotubes)CNT@PU(polyurethane)coatings.It was demonstrated that the CNT@PU coatings with 64%soft segment content possessed the preferable bonding strength(5B)with metal substrates.The multi-walled carbon nanotubes,as additive materials,were used to construct the microscopic structures of the coating surfaces,which made polyurethane surface superhydrophobic(water contact angle being 156.9°,and water sliding angle being 4.3°).Furthermore,the high bonding strength between CNT and coating matrix led to robust mechanical durability of supertiydrophobic CNT@PU coatings,and the coatings remained superhydrophobicity after 10 cycles of abrasion under 100 g load pressure.Also,the superhydrophobic coatings could well resist 5 cycles of tape-peeling action,and presented outstanding flexibility.The supernydrophobic CNT@PU coatings with high flexibility and mechanical durability could be applied to various substrates suggesting their big potential in future real-world application.

One-step modification method of a superhydrophobic surface for excellent antibacterial capability

In this study,micro/nanostructures are fabricated on the surface of 3Cr13 stainless steel via laser etching,and a superhydrophobic coating with silver nanoparticles(AgNPs)is prepared by utilizing the reduction–adsorption properties of polydopamine(PDA).We investigate the effect of soaking time from the“one-step method”on the reduction of nano-Ag,surface wettability,and antibacterial properties.Scanning electron microscopy is performed to analyze the distribution of nano-Ag on the surface,whereas X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy are used to analyze the crystal structures and chemical compositions of different surfaces.Samples deposited with PDA on their surface are soaked in a 1H,1H,2H,2H-perfluorodecyltriethoxysilane water–alcohol solution containing AgNO3 for 3 h.Subsequently,a“one-step method”is used to prepare low-adhesion superhydrophobic surfaces containing AgNPs.As immersion progresses,more AgNPs are deposited onto the surface.Compared with the polished surface,the samples prepared via the“one-step method”show significant antibacterial properties against both gram-negative Escherichia coli and gram-positive Staphylococcus aureus.The antibacterial properties of the surface improve as immersion progresses.

Robust superamphiphobic coatings with gradient and hierarchical architecture and excellent anti-flashover performances

Biomimetic superhydrophobic(SH)coatings have emerged as a promising alternative to traditional room temperature vulcanizing(RTV)silicone rubber coatings for improving the flashover strength of insulators.However,organic contamination occurs in outdoor applications and thus a superamphiphobic(SAP)surface is more desirable but not yet reported for improving flashover performance.Herein,we developed a novel anti-flashover technique by fabricating robust SAP coating with unique gradient and micro-nanoscale hierarchical architecture.The SAP coating was fabricated by sequentially spray-depositing a resin-based primer and a silica-based topcoat on substrates(i.e.,glass slides and insulators).The primer not only functions as an adhesive offering strong adhesion to the substrate but also offers a micromastoid-like structure facilitating the subsequent formation of hierarchical micro-nanostructure.The appropriate spraying pressure leads to a diffusion of the fluorocarbon-modified silica nanoparticles into the primer to form a unique gradient structure,by analogy to inserting bullets into a wood.These features render the SAP coating excellent robustness with strong abrasive resistance,excellent ultraviolet(UV)resistance,and excellent chemical and thermal stability.Pollution flashover property of the SAP coating was explored and compared with that of SH and RTV specimens,from which a novel organic-contamination model to evaluate the flashover performance was proposed.The coated SAP glass insulator demonstrated 42.9%pollution flashover voltage improvement than RTV-coated insulator.These stated unique features reveal the convincing potential of the present SAP coatings to be applied for not only outdoor transmission line insulators for antiflashover but also other fields for self-cleaning,anti-fouling,and anti-icing.

A Simple, Low-cost Method to Fabricate Drag-reducing Coatings on a Macroscopic Model Ship

A low-cost method was used to fabricate superhydrophobic coatings on a macroscopic model ship and the drag-reducing effect was investigated at both low and high speed. Hierarchical structures of the superhydrophobic copper coatings were characterized by means of scanning electron microscopy（SEM） and X-ray diffraction（XRD）. Drag coefficient tests on surfaces with different wettability（superhydrophilic, hydrophilic, hydrophobic and superhy- drophobic surfaces） showed that the as-prepared superhydrophobic surface exhibited a high remarkable drag reduction of 81% at a low speed of 1 mm/s. In the drag-reducing tests with model ship, the superhydrophobic coatings also exhibited around 16% drag reduction at a velocity of 0.3 m/s.