Interfacing superhydrophobic silica nanoparticle films with graphene and thermoplastic polyurethane for wear/abrasion resistance

Fabrication of bulk superhydrophobic wood by grafting porous poly(divinylbenzene) to wood structure using isocyanatoethyl methacrylate

Superhydrophobic treatment of wood can effectively reduce the interaction between wood and moisture, avoiding deformation, cracking, mould, and other defects caused by water absorption, which can extend the service life of wood and broaden the application field. Currently, the poor abrasion resistance of superhydrophobic wood is a crucial problem limiting its widespread application, and the preparation of superhydrophobic wood with robustness, abrasion resistance, and chemical resistance remains a huge challenge. In this work, robust bulk superhydrophobic wood with excellent abrasion resistance and chemical durability was fabricated by synthesizing porous poly(divinylbenzene) in wood cell cavities using graft copolymerization and solvothermal methods. The contact angles and rolling angles on the superhydrophobic wood surface were approximately 156° and 3°, respectively. Superhydrophobicity was carried through the entire structure of the wood. Even after severe damage by abrasion and sawing, as well as tests with organic solvents and harsh environments, the superhydrophobic properties of wood remained stable. Meanwhile, the superhydrophobic wood exhibited great self-cleaning and antifouling properties. In addition, the water uptake and dimensional stability of the wood were significantly improved. This work developed a simple, efficient, and durable strategy for the fabrication of superhydrophobic wood with robustness, abrasion resistance, and chemical resistance, which was expected to be applied to the wood industry to achieve the high-value applications of wood products and extend their service life.

A non-fluorinated superhydrophobic composite coating with excellent anticorrosion and wear-resistant performance

The facile and low-cost fabrication of fluorine-free superhydrophobic metal surfaces for anticorrosion remains a challenging issue. Here, we report a superhydrophobic coating based on polyacrylate/SiO₂ nanoparticles/graphene oxide sheets through a simple yet environmentally friendly method. The as-prepared composite coating sprayed on metal surfaces exhibits excellent superhydrophobic and corrosion-resistant properties. Furthermore, the coating surface possesses good anti-wear performance and remains superhydrophobic after harsh abrasion tests. Prospectively, the developed non-fluorinated superhydrophobic coating opens up opportunities for the application in industrial anticorrosion field.

Self-Stratified Versatile Coatings for Three-Dimensional Printed Underwater Physical Sensors Applications

A new strategy for developing versatile nanostructured surfaces utilizing the swelling of polymers in solvents is described. The self-stratified coating on 3D printed acrylonitrile-butadiene-styrene (ABS) copolymers with nanoparticles enables mechanically durable superhydrophobic characteristics. Unlike other methods, it was capable to produce superhydrophobicity on complex 3D structured surfaces. Mechanically durable superhydrophobic coatings that can withstand an abrasion cycle were obtained. Partial embedding of the nanoparticles into the ABS surface due to the swelling and self-stratification is considered as the reason for the increased mechanical strength of the coating. Utilizing this idea, the original concept of power-free physical sensors responding to changes in temperature, pressure, and surface tension was proposed.

High-Efficiency Electrospray Deposition Method for Nonconductive Substrates: Applications of Superhydrophobic Coatings

When highly insulating materials are used as substrates for electronic devices, manufacturing yields become worse, and electronic components are often damaged due to undissipated electrostatic charges on such substrates. In the case of electrospray deposition, the problem of undissipated charges is particularly vexing. If charges accumulated on the substrate are not properly compensated, a repulsive force is generated against the incoming charged droplets, which negatively affects the uniformity and deposition rate of the coating layer. In order to overcome this limitation, we demonstrated a new electrospray method, which can significantly increase the deposition efficiency even in the presence of accumulated charges on nonconductive substrates. A highly reliable superhydrophobic layer was uniformly deposited on highly insulating substrates, including printed circuit board (PCB), polyester (PET), and polyimide (PI) substrates.

Spray-On Nanocomposite Coatings: Wettability and Conductivity

Nanocomposite coatings, i.e., a combination of nanocompounds, and a polymer matrix together with suitable additives and solvents is a very versatile method for producing multifunctional coatings. Some of the most desired coating properties have a high repellency to liquids (e.g., superhydrophobic and/or superoleophobic) and electrical and thermal conductivities. From a practical perspective, coatings that can be sprayed are very suitable for large-scale production, conformity, and reduced time and cost. Carbon-based, metallic, and ceramic are the three groups of nanocompounds commonly used to formulate spray-on nanocomposite coatings. In this invited feature article, we discuss the applications, advantages, and challenges of using such nanocompounds to produce coatings with good water repellency or/and elevated electrical or/and thermal conductivities. We also discuss the role of additives and solvents briefly in relation to the properties of the coatings. Important spraying parameters, such as stand-off distance and its influence on the final coating properties, will also be examined. Our overall aim is to provide a guideline for the production of practical multifunctional nanocomposites utilizing carbon-based, metallic, or ceramic nanoparticles or nanofibers that covers both aspects of in-air wettability and conductivity under one umbrella.

Preparation of hydrophobic epoxy-polydimethylsiloxane-graphene oxide nanocomposite coatings for antifouling application

Epoxy-polydimethylsiloxane-graphene oxide (EPG) nanocomposite coatings were successfully developed by loading different wt% of graphene oxide nanosheets (GNs) into an epoxy-hydroxy-terminated-polydimethylsiloxane (EP-hPD) matrix via a facile in situ preparation technique. The inclusion of GNs into EPN led to an increase in modulus of elasticity and tensile strength up to 1570.46 MPa and 31.54 MPa, respectively, in the case of 1 wt% loading of GNs in the EP-hPD matrix. Also, an increase in the water contact angle from 90.1° to 115.2°, 104.5° and 101.7° was discerned at 1, 3 and 5 wt% loadings of GNs respectively. Taber abrasion results demonstrated a decrease in abrasion loss by 33.3% at 1 wt% loading of GNs in comparison to the unreinforced coating. An improvement in the glass transition temperature (T_g) was observed from 63.5 °C for the neat sample to 77.6 °C, 76.3 °C and 71.6 °C for the 1, 3 and 5 wt% EPG nanocomposites, respectively. An inevitable enhancement in the properties of the nanocomposites was affirmed due to the synergistic effect of GNs dispersed within the EP-hPD blend matrix. The prominent findings of this work include a minimum corrosion rate of 0.73 × 10^-2 mm per year and upgradation in the antifouling performance of the nanocomposite coatings in comparison to the neat coating.

Alkylated Nanofibrillated Cellulose/Carbon Nanotubes Aerogels Supported Form-Stable Phase Change Composites with Improved n-Alkanes Loading Capacity and Thermal Conductivity

The exploitation of phase change materials (PCMs) with excellent shape stability, considerable latent heat storage capacity, and superior thermal conductivity is essential for their applications in heat storage and thermal regulation. Here, form-stable composite PCMs based on n-octacosane, nanofibrillated cellulose (NFC), and carbon nanotubes (CNTs) were successfully obtained by impregnating n-octacosane into the alkylated NFC/CNTs hybrid aerogels. The three-dimensional interconnected porous aerogels could adequately support the melted n-octacosane and prevent the leakage problem due to strong capillary force and surface tension. After treatment with alkylated modification, the affinity between NFC/CNTs aerogels and n-alkanes was significantly improved, resulting in excellent shape stability, improved thermal reliability, and high n-alkanes loading capacity for the as-prepared composite PCMs. The differential scanning calorimetry analysis showed that composite PCMs based on the alkylated NFC/CNTs aerogels exhibited an extremely high phase change enthalpy ranging from 250.9 to 252.9 J/g. Furthermore, the thermal conductivity and photothermal conversion and storage efficiency of the synthesized PCMs were effectively enhanced by the introduction of CNTs. Thus, the synthesized composite PCMs exhibit considerable potential for practical application in heat storage and thermal regulation.

Preparation and Performance Test of the Super-Hydrophobic Polyurethane Coating Based on Waste Cooking Oil

In order to solve the problem of dust accumulation on the fin surface of a mine air cooler, a method of preparing super-hydrophobic polyurethane (SPU) coating based on waste cooking oil (WCO) was proposed. Firstly, the polyurethane prepolymer was synthesized with WCO as a raw material, and then the polyurethane prepolymer was modified with amino-terminated polydimethylsiloxane (ATP) to obtain SPU emulsion. The chemical structure and thermal stability of SPU were characterized by infrared spectrum and thermogravimetric analysis. A series of nanocomposites were prepared by combining modified silicon carbide (APT-SiC) particles and SPU emulsions. According to the parameters of pull-off strength, contact angle, sliding angle and thermal conductivity, the filler ratio of nanocomposites was optimized. The test results show that when the content of APT-SiC particles is 20 wt %, super-hydrophobic polyurethane coating can be obtained. The coating has good pull- off strength and thermal conductivity, and the contact angle and sliding angle are 161° and 3°, respectively. In addition, the practical application of the super-hydrophobic polyurethane coating was tested by related experiments. The experimental results show that the coating has good self-cleaning, wear resistance and anti-corrosion performance, can meet the requirements of air coolers in special environments, and has great application prospects.

Comparison of hydrophobicity and durability of functionalized aluminium oxide nanoparticle coatings with magnetite nanoparticles-links between morphology and wettability

HYPOTHESIS

The wetting characteristics of coatings created using functionalised nanoparticles and adhesive resins, depends strongly on the particle distribution within the surface layers. Although it has been shown that commercially available adhesives improve the durability of hydrophobic nanoparticle coatings, the wettability of these surfaces is governed by the agglomeration behaviour of the particles within the adhesive. As a consequence of this, coatings where the particles are highly agglomerated within the adhesive show lower hydrophobicity.

EXPERIMENTS

The morphology and chemical composition of coatings formed from carboxylate functionalised Al₂O₃ and magnetite (Fe₃O₄) nanoparticles and epoxy resin on plastic was studied using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Water contact angle (WCA) measurements were used to investigate how the coatings' morphological characteristics and loading of the particles within the surface layers influenced their wettability. Infrared (IR) spectroscopy and thermogravimetric analysis (TGA) were used to study carboxylate adsorption onto the magnetite nanoparticles.

FINDINGS

Combining the Al₂O₃ nanoparticles with epoxy resin was observed to create highly hydrophobic coatings that displayed water contact angles (WCAs) between 145 and 150°. These coatings displayed good durability when sonicated in isopropanol and wiped with tissue. By comparison, coatings formed from the magnetite nanoparticles were substantially less hydrophobic and displayed WCAs between 75 and 125° when combined with epoxy resin. SEM revealed that the magnetite nanoparticles in the coatings were present as large agglomerates. By comparison, coatings formed from the Al₂O₃ nanoparticles showed a more homogenous particle distribution. Furthermore, XPS showed that the resin engulfed the magnetite nanoparticles to a far greater extent. The difference in wetting behaviour of these coatings is largely attributed to their different morphologies, since the particles are similar sizes and TGA shows that the particles possess similar carboxylate grafting densities. The uneven distribution of nanoparticles in the magnetite/epoxy resin coating is due to the particles' magnetic properties, which drive nanoparticle agglomeration as the coatings solidify. This work demonstrates that it is important to consider inter-particle interactions when fabricating low wettability composite coatings.

Synthesis of Silane Functionalized Graphene Oxide and Its Application in Anti-Corrosion Waterborne Polyurethane Composite Coatings

In this study, novel silane functionalized graphene oxide (PVSQ-GO) composite material is synthesized through the hydrolysis condensation reaction of vinyl triethoxysilane monomers occurred at the surface of graphene oxide. Results obtained from FTIR, Raman, X-ray photoelectronic spectroscopy (XPS), XRD and TGA measurements reveal that polyvinyl sesquisiloxane microspheres adhere to graphene oxide lamellae in the form of chemical bonds. Meanwhile, it is intuitive that abundant polyvinyl sesquisiloxane microspheres stick to the surface of graphene oxide and increase the thickness of the flake. Modified graphene oxide changes from hydrophilicity to hydrophobicity were owing to the existence of polyvinyl sesquisiloxane microspheres on the surface of graphene oxide (GO). PVSQ-GO composite exhibited good dispersion in eco-friendly waterborne polyurethane coating. Electrochemical impedance spectroscopy manifested that the anti-corrosion performance of waterborne polyurethane (WPU) coating embedded at 0.5 wt.% PVSQ-GO composite improved effectively. Tafel curves reveal that 0.5 wt.% PVSQ-GO/WPU coating specimen shows the lowest corrosion rate of 8.95 × 10−5 mm/year when compared with the other coating specimens. The good anti-corrosion abilities of PVSQ-GO composite coating can be interpreted as the good compatibility between PVSQ-GO composite and waterborne polyurethane, however, the intrinsic hydrophobicity of PVSQ-GO composite is beneficial to inhibit the permeation of corrosive medium and thus slows down the corrosion rate.

Assembly Mechanism and the Morphological Analysis of the Robust Superhydrophobic Surface

Robust superhydrophobic surfaces are fabricated on different substrates by a scalable spray coating process. The developed superhydrophobic surface consists of thin layers of surface functionalized silica nanoparticle (SiO2) bound to the substrate by acrylate-polyurethane (PU) binder. The influence of the SiO2/PU ratio on the superhydrophobicity, and the robustness of the developed surface, is systematically analyzed. The optimized SiO2/PU ratio for prepared superhydrophobic surfaces is obtained between 0.9 and 1.2. The mechanism which yields superhydrophobicity to the surface is deduced for the first time with the help of scanning electron microscopy and profilometer. The effect of mechanical abrasion on the surface roughness and superhydrophobicity are analyzed by using profilometer and contact angle measurement, respectively. Finally, it is concluded that the binder plays a key role in controlling the surface roughness and superhydrophobicity through the capillary mechanism. Additionally, the reason for the reduction in performance is also discussed with respect to the morphology variation.

Immobilization of rubber additive on graphene for high-performance rubber composites

It is still a challenge to achieve simultaneous improvements in aging resistance, mechanical strength, thermal conductivity and dielectric constant of rubber composites via incorporation of graphene obtained by conventional methods. Herein, an effective and green method was proposed to simultaneously reduce and functionalize graphene oxide (GO) with 2-mercaptobenzimidazole (antioxidant MB) via a one-pot method. GO was successfully reduced by MB which was also chemically grafted on the reduced GO (G-MB). G-MB sheets were uniformly dispersed in rubber with strong interfacial interaction, and graphene-graphene conductive paths were formed through intermolecular H-bonding between the grafted antioxidant molecules. Consequently, rubber composites with G-MB showed higher thermal conductivity, mechanical strength and dielectric constant than rubber composites with hydrazine hydrate reduced GO (rGO). Moreover, the thermo-oxidative aging resistance of rubber composites with G-MB was also superior to that of rubber composites with rGO because of the elimination of blooming effect of the grafted MB molecules. Thus, this work may open a new way for the eco-friendly functionalization and reduction of GO and may boost the development of high-performance, functional graphene-elastomer composites.

Reactive silica nanoparticles turn epoxy coating from hydrophilic to super-robust superhydrophobic

Superhydrophobic organic-inorganic hybrid nanocomposite coatings have received much attention because they possess the advantages of both inorganic and organic materials. Nevertheless, it is difficult to achieve strong bonding of inorganic nanoparticles to the polymer matrix while maintaining a sufficiently rough structure to impart superhydrophobicity. In this study, we fabricated silica nanoparticles with surface reactive groups that can further react with the epoxy resin. Thus, the hydrophobic silica nanoparticles were stably anchored and stabilized in the cured resin matrix while forming nanometer-scale roughness structures. The obtained silica-decorated epoxy resin coating shows great durability and water-repellency after mechanical abrasions and has superior adhesion to the substrate.

Abrasion Resistance of Superhydrophobic Coatings on Aluminum Using PDMS/SiO2

Superhydrophobic coatings have shown tremendous improvement in the usability of metals such as aluminum. These coatings are capable of adding attractive features such as self-cleaning, anti-corrosion, and anti-biofouling to the array of diverse features that aluminum possesses, including lightweight and high ductility. For superhydrophobic surfaces, having considerable abrasion resistance is as important as achieving a high contact angle. In this work, two types of coatings have been prepared, each composed of functionalized silica nanoparticles along with polydimethylsiloxane (PDMS) dispersed in ethanol, and their superhydrophobicity and abrasion characteristics have been investigated. The same silica nanoparticles are present in each coating, but each has a different proportion of the PDMS base to its curing agent. The surface morphology of the coatings was studied with the aid of a scanning electron microscope (SEM) and an atomic force microscope (AFM). The surface chemical composition was characterized using an energy dispersive X-ray spectroscope (EDX). The prepared coatings were analyzed for their degree of superhydrophobicity, abrasion resistance and adhesion characteristics. In addition, atomic force microscopy was used to understand the adhesion characteristics of the coatings.

Design and fabrication of vapor-induced superhydrophobic surfaces obtained from polyethylene wax and silica nanoparticles in hierarchical structures

The present work reported a simple and effective approach to fabricate a low-cost, self-cleaning and mechanically durable superhydrophobic coating. The coating was prepared by dip-coating certain substrates in an ethyl acetate suspension of silica nanoparticles (SiO₂), hydroxyl acrylic resin, cross-linking agent and polyethylene wax (PEW). Through the control of the cooling and drying process, vapor-induced PEW micro-clusters were formed on the surfaces during the evaporation of ethyl acetate, and uniform carpet-like hierarchical structures were finally obtained by properly adjusting the dosage of PEW. Under the synergistic effect of hydrophobic SiO₂ nanoparticles and PEW micro-clusters, the composite coating exhibited a remarkable superhydrophobicity with a contact angle of 163° ± 5° with 25 wt% content of PEW, as well as preeminent self-cleaning properties against various food liquids. Moreover, the coating still maintained its surface cleanliness when immersed in the cyclohexane or hexadecane, indicating a superior self-cleaning property against solvent-contamination. The mechanical durability test showed that the coating still kept its excellent water repellency after fairly intensive knife-scratching, tape peeling and 25 cycles of sandpaper abrasion under 100 g of loading, indicating a quite admirable mechanical durability. The facile preparation and high-performance of the coating make it quite suitable for manufacture on a large scale, which is favorable for the development of superhydrophobic coatings.

Fabrication of superhydrophobic surfaces based on PEW and SiO₂ though a vapor-induced method.