Superhydrophobic Surface-Assisted Preparation of Microspheres and Supraparticles and Their Applications

Superhydrophobic surface(SHS) has been well developed, as SHS renders the property of minimizing the water/solid contact interface. Water droplets deposited onto SHS with contact angles exceeding 150°, allow them to retain spherical shapes, and the low adhesion of SHS facilitates easy droplet collection when tilting the substrate. These characteristics make SHS suitable for a wide range of applications. One particularly promising application is the fabrication of microsphere and supraparticle materials. SHS offers a distinct advantage as a universal platform capable of providing customized services for a variety of microspheres and supraparticles. In this review, an overview of the strategies for fabricating microspheres and supraparticles with the aid of SHS, including cross-linking process, polymer melting,and droplet template evaporation methods, is first presented. Then, the applications of microspheres and supraparticles formed onto SHS are discussed in detail, for example, fabricating photonic devices with controllable structures and tunable structural colors, acting as catalysts with emerging or synergetic properties, being integrated into the biomedical field to construct the devices with different medicinal purposes, being utilized for inducing protein crystallization and detecting trace amounts of analytes. Finally,the perspective on future developments involved with this research field is given, along with some obstacles and opportunities.

Robustα-Fe_(2)O_(3)/Epoxy Resin Superhydrophobic Coatings for Anti-icing Property

α-Fe_(2)O_(3)/epoxy resin composite superhydrophobic coating was prepared withα-Fe_(2)O_(3) nanoparticles and epoxy resin by spin coating method.The coating without epoxy resin has higher contact angle(CA)and lower ice adhesion strength(IAS),but the mechanical properties are poor.Theα-Fe_(2)O_(3)/epoxy resin composite superhydrophobic coating exhibits good mechanical durability.In addition,compared with the bare aluminum substrate,the Ecorr of the composite coating is positive and the Jcorr is lower.The inhibition efficiency of the composite coating is as high as 99.98%in 3.5 wt%NaCl solution.The difference in the microstructure caused by the two preparation methods leads to the changes in mechanical properties and corrosion resistance of composite superhydrophobic coating.

Superhydrophobic Co/Fe sulfide nanoparticles and single-atoms doped carbon nanosheets composite air cathode for high-performance zinc-air batteries

Development of a high-performance bifunctional catalyst is essential for the actual implementation of zinc-air batteries in practical applications.Herein,a bifunctional cathode of Co_(3)S_(4)/FeS heterogeneous nanoparticles embedded in Co/Fe single-atom-loaded nitrogen-doped carbon nanosheets is designed.Cobalt-iron sulfides and single atomic sites with Co-N_(4)/Fe-N_(4)configurations are confirmed to coexist on the carbon matrix by EXAFS spectroscopy.3D self-supported super-hydrophobic multiphase composite cathode provides abundant active sites and facilitates gas–liquid-solid three-phase interface reactions,resulting in excellent electrocatalytic activity and batteries performance,i.e.,an OER overpotential(η_(10))of 260 mV,a half-wave potential(E_(1/2))of 0.872 V for ORR,aΔE of 0.618 V,and a discharge power density of 170 mW cm^(−2),a specific capacity of 816.3 mAh g^(−1).DFT analysis shows multiphase coupling of sulfide heterojunction through single-atomic metal doped carbon nanosheets reduces offset on center of electronic density of states before and after oxygen adsorption,and spin density of adsorbed oxygen with same spin orientation,leading to weakened charge/spin interactions between adsorbed oxygen and substrate,and a lowered oxygen adsorption energy to accelerate OER/ORR.

Fabrication and anti-corrosion performance of superhydrophobic silane film on sintered NdFeB

An eco-friendly superhydrophobic protective film(DTMS/TEOS silane film)was fabricated on sintered NdFeB substrate through the utilization of electrochemically assisted deposition technology.The structure,properties,and film-forming mechanism of dodecyltrime-thoxysilane(DTMS)/tetraethoxysilane(TEOS)silane films were comprehensively analyzed using Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS).Based on the test results,it can be determined that this film has a superhydrophobic property with a hydrophobicity angle of 152°.This special property can be attributed to the long alkyl chains in the DTMS molecule,the rough morphology,and the low surface energy of the DTMS/TEOS silane film.The surface of sintered NdFeB is coated with a layered three-dimensional network silane film that forms through the condensation of silanol substances.This film provides excellent corrosion resistance to the sintered NdFeB substrate,reducing its corrosion current density to 2.02×10~(-6)A/cm~2.Moreover,the impact of film on the magnetic characteristics of sintered NdFeB was assessed and found to be minimal.

Superhydrophobic melamine sponge prepared by radiation-induced grafting technology for efficient oil-water separation

This paper presents a superhydrophobic melamine(ME)sponge(ME-g-PLMA)prepared via high-energy radiation-induced in situ covalent grafting of long-alkyl-chain dodecyl methacrylate(LMA)onto an ME sponge for efficient oil–water separation.The obtained ME-g-PLMA sponge had an excellent pore structure with superhydrophobic(water contact angle of 154°)and superoleophilic properties.It can absorb various types of oils up to 66–168 times its mass.The ME-g-PLMA sponge can continuously separate oil slicks in water by connecting a pump or separating oil underwater with a gravity-driven device.In addition,it maintained its highly hydrophobic properties even after long-term immersion in different corrosive solutions and repeated oil adsorption.The modified ME-g-PLMA sponge exhibited excellent separation properties and potential for oil spill cleanup.

Characterization of Flame Retardancy and Oil-Water Separation Capacity of Superhydrophobic Silylated Melamine Sponges

A silylated melamine sponge(SMS)was prepared by two simple steps,namely,immersion and dehydration of a melamine sponge coated with methyltrichlorosilane.The silylated structure of SMS was characterized by FT-IR(Fourier-transform infrared)spectroscopy,SEM(Scanning electron microscopy)and in terms of water contact angles.Its oil-water absorption and separation capacities were measured by FT-IR and UV-visible spectrophoto-metry.The experimental results have shown that oligomeric silanol covalently bonds by Si-N onto the surface of melamine sponge skeletons.SMS has shown superhydrophobicity with a water contact angle exceeding 150°±1°,a better separation efficiency with regard to diesel oil(by 99.31%(wt/wt%)in oil-water mixture and even up to 99.99%(wt/wt%)for diesel oil in its saturated aqueous solution.Moreover,SMS inherited the intrinsicflame retardancy of the melamine sponge.In general,SMS has shown superhydrophobicity,high porosity,excellent selectivity,remarkable recyclability,and better absorption capacity for various oils and organic solvents,and a high separation efficiency for oil in saturated aqueous solutions.

Corrosion resistance and anti-soiling performance of micro-arc oxidation/graphene oxide/stearic acid superhydrophobic composite coating on magnesium alloys

Magnesium(Mg)alloys,the lightest metal construction material used in industry,play a vital role in future development.However,the poor corrosion resistance of Mg alloys in corrosion environments largely limits their potential wide applications.Therefore,a micro-arc oxidation/graphene oxide/stearic acid(MAO/GO/SA)superhydrophobic composite coating with superior corrosion resistance was fabricated on a Mg alloy AZ91D through micro-arc oxidation(MAO)technology,electrodeposition technique,and self-assembly technology.The composition and microstructure of the coating were characterized by scanning electron microscopy,X-ray diffraction,energy dispersive spectroscopy,and Raman spectroscopy.The effective protection of the MAO/GO/SA composite coating applied to a substrate was evaluated using potentiodynamic polarization,electrochemical impedance spectroscopy tests,and salt spray tests.The results showed that the MAO/GO/SA composite coating with a petal spherical structure had the best superhydrophobicity,and it attained a contact angle of 159.53°±2°.The MAO/GO/SA composite coating exhibited high resistance to corrosion,according to electrochemical and salt spray tests.

ZIF-8-based micro-arc oxidation composite coatings enhanced the corrosion resistance and superhydrophobicity of a Mg alloy

Mg alloys are considered the most promising engineering materials because of their unique properties.However,the uncontrolled corrosion rate of these alloys limits their applications.Therefore,in this study,a micro-arc oxidation layer was used as a transition layer to“directly”grow a zinc-based metal-organic framework(MOF)composite coating on the surface of a Mg alloy(AZ91D).Herein,the two zeolitic imidazolate framework(ZIF-8)coatings with different morphologies were separately prepared by homologous metal oxide induction and a one-step in-situ growth method.The superhydrophobic composite coating showed strong hydrophobicity and self-cleaning properties,which could prevent the penetration of water and corrosive ions(Cl^(−))into the surface of AZ91D.Electrochemical tests demonstrated that the super-hydrophobic composite coatings greatly enhanced the corrosion resistance of AZ91D,and the corrosion current density decreased from 10^(−5)to 10^(−9)A/cm^(2).These results indicate that the ZIF-8 coatings are beneficial for improving the hydrophobicity and enhancing the corrosion resistance of Mg alloys.Therefore,MOF composite coatings provide a new strategy that can be used to prepare multifunctional anticorrosion coatings on metal substrates.

Recent advances in preparation of metallic superhydrophobic surface by chemical etching and its applications

In the past few decades,inspired by the superhydrophobic surfaces(SHPS)of animals and plants such as lotus leaves,rose petals,legs of water striders,and wings of butterflies,preparing metal materials with metallic SHPS(MSHPS)have attracted great research interest,due to the great prospect in practical applications.To obtain SHPS on conventional metal materials,it is necessary to construct rough surface,followed by modification with low surface energy substances.In this paper,the action mechanism and the current research status of MSHPS were reviewed through the following aspects.Firstly,the model of wetting theory was presented,and then the progress in MSHPS preparation through chemical etching method was discussed.Secondly,the applications of MSHPS in self-cleaning,anti-icing,corrosion resistance,drag reduction,oil-water separation,and other aspects were introduced.Finally,the challenges encountered in the present application of MSHPS were summarized,and the future research interests were discussed.

ZnO@ZIF-8 core-shell structure nanorods superhydrophobic coating on magnesium alloy with corrosion resistance and self-cleaning

A longstanding quest in material science has been the development of superhydrophobic coating based on a single material, without the requirement of fluorination or silane treatment. In this work, the micro-arc oxidation(MAO) coating as transition layer can effectively enhance the bonding force of the superhydrophobic coating. The semiconductor@metal organic frameworks(MOFs) core-shell structure was synthesized by a simple self-templating method, and obtained ZnO@2-methylimidazole zinc salt(ZIF-8) nanorods array on magnesium(Mg)alloy. ZnO nanorods not only act as the template but also provide Zn^(2+) for ZIF-8. In addition, we proved that the ligand concentration,synthesis time and temperature are the keys to the preparation of ZnO@ZIF-8 nanorods. As we expect, the ZnO@ZIF-8 nanorods array can trap air in the gaps to form an air layer, and the coating exhibits superhydrophobic properties(154.81°). Excitingly, ZnO@ZIF-8 nanorods array shown a superhydrophobic property, without the requirement of fluorination or silane treatment. The results shown that the coating has good chemical stability and self-cleaning performance. Meanwhile, the corrosion resistance has been significantly improved, R_(ct) was increased from 1.044×10^(3) to 1.414×10^(6) Ω/cm^(2) and I_(corr) was reduced from 4.275×10^(-5) to 5.611×10^(-9)A/cm^2. Therefore, the semiconductor@MOFs core-shell structure has broad application prospects in anti-corrosion.

New superhydrophobic composite coatings on Mg-Mn-Ce magnesium alloy

A novel combined method for the formation of composite coatings on the Mg-Mn-Ce alloy is developed.Ceramic like matrix was formed on the Mg alloy surface by the plasma electrolytic oxidation.Then the samples were subsequently processed by dip-coating in an alcohol suspension of superdispersed polytetrafluoroethylene and spraying with the tetrafluoroethylene telomers solution.SEM,OSP,and SPM was used to study structure of formed surfaces.It was established by measurements of CA and CAH,as well as surface free energy calculations that formed coatings demonstrate superhydrophobic properties due to the presence of an irregular hierarchical surface structure and low surface free energy of fluoropolymers.The coating preserves its hydrophobic properties after exposure to high and low temperatures,for a long time as well as being in corrosive environments.EDS and XRD data analysis confirmed the presence of organofluorine compounds in the composite layers,including in the form of crystalline polytetrafluoroethylene.Using potentiodynamic polarization test and EIS,it was found that the resulting coatings significantly increase the corrosion resistance of Mg material.These data are also confirmed by salt spray tests for 40 days.Incorporation of fluoropolymers additionally decrease coatings coefficient of friction.

Photothermal superhydrophobic copper nanowire assemblies: fabrication and deicing/defrosting applications

Ice and frost buildup continuously pose significant challenges to multiple fields.As a promising de-icing/defrosting alternative,designing photothermal coatings that leverage on the abundant sunlight source on the earth to facilitate ice/frost melting has attracted tremendous attention recently.However,previous designs suffered from either localized surface heating owing to the limited thermal conductivity or unsatisfied meltwater removal rate due to strong water/substrate interaction.Herein,we developed a facile approach to fabricate surfaces that combine photothermal,heat-conducting,and superhydrophobic properties into one to achieve efficient de-icing and defrosting.Featuring copper nanowire assemblies,such surfaces were fabricated via the simple template-assisted electrodeposition method,allowing us to tune the nanowire assembly geometry by adjusting the template dimensions and electrodeposition time.The highly ordered copper nanowire assemblies facilitated efficient sunlight absorption and lateral heat spreading,resulting in a fast overall temperature rise to enable the thawing of ice and frost.Further promoted by the excellent water repellency of the surface,the thawed ice and frost could be spontaneously and promptly removed.In this way,the all-in-one design enabled highly enhanced de-icing and defrosting performance compared to other nanostructured surfaces merely with superhydrophobicity,photothermal effect,or the combination of both.In particular,the defrosting efficiency could approach∼100%,which was the highest compared to previous studies.Overall,our approach demonstrates a promising path toward designing highly effective artificial deicing/defrosting surfaces.

Facile fabrication of durable superhydrophobic fabrics by silicon polyurethane membrane for oil/water separation

Nowadays, oil contamination has become a major reason for water pollution, and presents a global environmental challenge. Although many efforts have been devoted to the fabrication of oil/water separation materials, their practical applications are still hindered by their weak durability, poor chemical tolerance,environmental resistance, and potential negative impact on health and the environment. To overcome these drawbacks, this work offers a facile method to fabricate the eco-friendly and durable oil/water separation membrane fabrics by alkaline hydrolysis and silicon polyurethane coating. The X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy results demonstrate that silicon polyurethane membrane could be coated onto the surface of hydrolyzed polyester fabric and form a micro-/nano-scaled hierarchical structure. Based on this, the modified fabric could have a stable superhydrophobic property with a water contact angle higher than 150°, even after repeated washing and mechanical abrasion 800 times, as well as chemical corrosion. Moreover, the modified fabrics show excellent oil/water separation efficiency of up to 99% for various types of oil–water mixture. Therefore, this durable, eco-friendly and cost-efficient superhydrophobic fabric has great potential in large-scale oil/water separation.

Fabrication of adsorbents with enhanced CuⅠ stability: Creating a superhydrophobic microenvironment through grafting octadecylamine

In atmospheric conditions, CuⅠis easily oxidized to CuⅡdue to the coexistence of moisture and oxygen.The poor oxidation inhibition of CuⅠrestricts the practical application of CuⅠ-containing materials.Herein we introduce an approach to construct a superhydrophobic microenvironment in CuⅠfunctionalized metal–organic frameworks by coordinatedly grafting organic amine compounds onto open metal sites(OMSs), which can hinder the accessibility of moisture to pores thereby enhancing the stability of CuⅠ. As a proof of concept, MIL-101(Cr) with abundant OMSs and octadecylamine(OA)with long hydrophobic alkyl groups are used as carrier and surface coating. As superhydrophobic porous materials, the resultant CuⅠM-OA exhibits improved CuⅠstability in addition to retaining high crystallinity and intact porosity while almost all CuⅠis oxidized in hydrophilic CuⅠM upon exposure in a humid atmosphere for 30 h. CuⅠM-OA owns excellent adsorption desulfurization performance(ADS) with regard to thiophene, benzothiophene, and 4,6-dimethyl dibenzothiophene. Even from hydrated fuel, the adsorption performance of CuⅠM-OA maintains well while the adsorption capacity of CuⅠM decreases to 7% after4 cycles. The remarkable moisture resistance, CuⅠstability, and high porosity make the current adsorbent CuⅠM-OA highly promising for the practical ADS process.

The superhydrophobic sponge decorated with Ni-Co double layered oxides with thiol modification for continuous oil/water separation

In this paper, the superhydrophobic polyurethane sponge(SS-PU) was facilely fabricated by etching with Jones reagent to bind the nanoparticles of Ni-Co double layered oxides(LDOs) on the surface, and following modification with n-dodecyl mercaptan(DDT). This method provides a new strategy to fabricate superhydrophobic PU sponge with a water contact angle of 157° for absorbing oil with low cost and in large scale. It exhibits the strong absorption capacity and highly selective characteristic for various kinds of oils which can be recycled by simple squeezing. Besides, the as-prepared sponge can deal with the floating and underwater oils, indicating its application value in handling oil spills and domestic oily wastewater. The good self-cleaning ability shows the potential to clear the pollutants due to the ultralow adhesion to water. Especially, the most important point is that the superhydrophobic sponge can continuously and effectively separate the oil/water mixture against the condition of turbulent disturbance by using our designed device system, which exhibit its good superhydrophobicity, strong stability.Furthermore, the SS-PU still maintained stable absorption performance after 150 cycle tests without losing capacity obviously, showing excellent durability in long-term operation and significant potential as an efficient absorbent in large-scale dispose of oily water.

Green Superhydrophobic Paper with Self-cleaning Properties Prepared via One-step Impregnation

In this study,a green and pollution-free multifunctional superhydrophobic paper-based material was prepared using a simple and efficient dipping method.The superhydrophobic paper with a water contact angle(WCA)of 160°was prepared by attaching micro-and nanocomposite particles,made of stearic acid-modified chitosan and two kinds of titanium dioxide(TiO_(2))nanoparticles of different sizes,to a paper substrate.The surface morphology,elemental composition,and wetting properties of the coatings were examined using scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FT-IR),and contact angle measurements.Additionally,superhydrophobic coatings exhibited good self-cleaning properties,liquid repellency,ease of repair,and antifouling properties in organic solutions.

Construction of Renewable Superhydrophobic Surfaces via Thermally Induced Phase Separation and Mechanical Peeling

We report a simple preparation method of a renewable superhydrophobic surface by thermally induced phase separation （TIPS） and mechanical peeling. Porous polyvinylidene fluoride （PVDF） membranes with hierarchical structures were prepared by a TIPS process under different cooling conditions, which were confirmed by scanning electron microscopy and mercury intrusion porosimetry. After peeling off the top layer, rough structures with hundreds of nanometers to several microns were obtained. A digital microscopy determines that the surface roughness of peeled PVDF membranes is much higher than that of the original PVDF membrane, which is important to obtain the superhydrophobicity. Water contact angle and sliding angle measurements demonstrate that the peeled membrane surfaces display super- hydrophobicity with a high contact angle （152°） and a low sliding angle （7.2°）. Moreover, the superhydrophobicity can be easily recovered for many times by a simple mechanical peeling, identical to the original superhydrophobicity. This simple preparation method is low cost, and suitable for large-scale industrialization, which may offer more opportunities for practical applications.

Superhydrophobicity of Bionic Alumina Surfaces Fabricated by Hard Anodizing

Bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique. The convex domes on the bionic sample were fabricated by compression molding under a compressive stress of 92.5 MPa. The water contact angles of the as-anodized bionic samples were measured using a contact angle meter （JC2000A） with the 3μL water drop at room temperature. The measurement of the wetting property showed that the water contact angle of the unmodi- fied as-anodized bionic alumina samples increases from 90° to 137° with the anodizing time. The increase in water contract angle with anodizing time arises from the gradual formation of hierarchical structure or composite structure. The structure is composed of the micro-scaled alumina columns and pores. The height of columns and the depth of pores depend on the ano- dizing time. The water contact angle increases significantly from 96° to 152° when the samples were modified with self-assembled monolayer of octadecanethiol （ODT）, showing a change in the wettability from hydrophobicity to su- per-hydrophobicity. This improvement in the wetting property chemical modification. is attributed to the decrease in the surface energy caused by the

Modeling Superhydrophobic Contact Angles and Wetting Transition

It is well known that surface roughness has a very important effect on superhydrophobicity.The Wenzel and Cassie-Baxter models,which correspond to the homogeneous and heterogeneous wetting respectively,are currently primary instructions for designing superhydrophobic surfaces.However,the particular drop shape that a drop exhibits might depend on how it is formed. A water drop can occupy multiple equilibrium states,which relate to different local minimal energy.In some cases,both equilibrium states can even co-exist on a same substrate.Thus the apparent contact angles may vary and have different values.We discuss how the Wenzel and Cassie-Baxter equations determine the homogeneous and heterogeneous wetting theoretically. Contact angle analysis on hierarchical surface structure and contact angle hysteresis has been put specific attention.In particular, we study the energy barrier of transition from Cassie-Baxter state to Wenzel state,based on existing achievement by previous researchers,to determine the possibility of the transition and how it can be interpreted.It has been demonstrated that surface roughness and geometry will influence the energy required for a drop to get into equilibrium,no matter it is homogeneous or heterogeneous wetting.

Fabrication of corrosion-resistant superhydrophobic coating on magnesium alloy by one-step electrodeposition method

A one-step electrodeposition method was used to construct a superhydrophobic coating on the surface of magnesium alloy.Using magne-sium nitrate and ethanol solution of stearic acid as electrolyte,four groups of electrolytes with different ratios of stearic acid and magnesium nitrate were designed to explore the influence of electrolyte to the process.The contact angles of the four coating samples were 136.4±5.8°,152.7±2.8°,156.2±4.9°and 155.1±4.4°The addition of magnesium nitrate in the solution increased the hydrogen evolution reaction in the electrodeposition process,which was not conducive to electrodeposition process.During the deposition process,the sample prepared in a molar ratio of stearic acid to magnesium nitrate of 10:1 had the best corrosion resistance,and its corrosion circuit density was 3.74×10^(−8)A/cm^(2),far lower than the corrosion current density of the magnesium alloy substrate.