A multifunctional super-hydrophobic coating based on PDA modified MoS2 with anti-corrosion and wear resistance

Recyclable Superhydrophobic Surface Prepared via Electrospinning and Electrospraying Using Waste Polyethylene Terephthalate for Self-Cleaning Applications

Superhydrophobic surfaces, i.e., surfaces with a water contact angle (WCA) ≥ 150°, have gained much attention as they are multifunctional surfaces with features such as self-cleaning, which can be useful in various applications such as those requiring waterproof and/or protective films. In this study, we prepared a solution from recycled polyethylene terephthalate (PET) and fabricated a superhydrophobic surface using electrospinning and electrospraying processes. We observed that the fabricated geometry varies depending on the solution conditions, and based on this, we fabricated a hierarchical structure. From the results, the optimized structure exhibited a very high WCA (>156.6°). Additionally, our investigation into the self-cleaning functionality and solar panel efficiency of the fabricated surface revealed promising prospects for the production of superhydrophobic surfaces utilizing recycled PET, with potential applications as protective films for solar panels. Consequently, this research contributes significantly to the advancement of environmentally friendly processes and the progress of recycling technology.

A wear and heat-resistant hydrophobic fluoride-free coating based on modified nanoparticles and waterborne-modified polyacrylic resin

Hydrophobic coatings have attracted extensive research due to their broad application prospects. However, hydrophobic coatings in practical applications are often limited by their insufficient stability and are difficult to be applied on a large scale. In this regard, wear and heat resistance are key aspects that must be considered. In this paper, a method for preparing a robust hydrophobic coating with modified ZrO₂ particles as the core component and modified acrylic resin is proposed. First, γ-aminopropyltriethoxysilane (APTES) was used to silanize ZrO₂ to obtain Si-ZrO₂ nanoparticles, which were grafted with amino groups. Then, the nanoparticles reacted with isocyanates to be grafted with hydrophobic groups. A simple spray method was developed to deposit a hydrophobic (141.8°) coating using the mixture containing the modified nanoparticles and non-fluorinated water-based silicon-modified acrylic resin (WSAR) that was prepared by free radical polymerization. The obtained coating exhibited a rough surface and the particles and resin were closely combined. Compared with pure resin coating, the composite coating exhibited 150% enhancement in wear resistance and it could wear 45 meters at a pressure of 20 kPa. Moreover, the coating could maintain the hydrophobic property even when it lost 70% quality or after it was heated at 390 °C. The thermogravimetric results showed that the temperature could reach 400 °C before the quality of the fluorine-free coating dropped to 90%. In addition, the coating could easily take away graphite or silicon carbide powder under the impact of water droplets, showing excellent self-cleaning performance.

Fabrication and Characterization of Superhydrophobic Al-Based Surface Used for Finned-Tube Heat Exchangers

Enhancing the heat transfer performance of heat exchangers is one of the main methods to reduce energy consumption and carbon emissions in heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. Wettability modified surfaces developed gradually may help. This study aims to improve the performance of heat exchangers from the perspective of component materials. The facile and cost-effective fabrication method of superhydrophobic Al-based finned-tube heat exchangers with acid etching and stearic acid self-assembly was proposed and optimized in this study, so that the modified Al fins could achieve stronger wettability and durability. The effect of process parameters on the wettability of the Al fins was by response surface methodology (RSM) and variance analysis. Then, the modified fins were characterized by field-emission scanning electron microscopy (FE-SEM), 3D topography profiler, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The durability of the superhydrophobic fins was investigated by air exposure, corrosion resistance, and mechanical robustness experiments. The RSM and variance analysis demonstrated that a water contact angle (WCA) of 166.9° can be obtained with the etching time in 2 mol/L HCl solution of 10.5 min, the self-assembly time in the stearic acid ethanol solution of 48 h, and drying under 73.0 °C. The surface morphology showed suitable micro-nano structures with a mean roughness (Ra) of 467.58 nm and a maximum peak-to-valley vertical distance (Rt) of 4.095 μm. The chemical component demonstrated the self-assembly of an alkyl chain. The WCAs declined slightly in durability experiments, which showed the feasibility of the superhydrophobic heat exchangers under actual conditions.

Biomimetic Approach for the Elaboration of Highly Hydrophobic Surfaces: Study of the Links between Morphology and Wettability

This investigation of morphology-wetting links was performed using a biomimetic approach. Three natural leaves' surfaces were studied: two bamboo varieties and Ginkgo Biloba. Multiscale surface topographies were analyzed by SEM observations, FFT, and Gaussian filtering. A PDMS replicating protocol of natural surfaces was proposed in order to study the purely morphological contribution to wetting. High static contact angles, close to 135∘, were measured on PDMS replicated surfaces. Compared to flat PDMS, the increase in static contact angle due to purely morphological contribution was around 20∘. Such an increase in contact angle was obtained despite loss of the nanometric scale during the replication process. Moreover, a significant decrease of the hysteresis contact angle was measured on PDMS replicas. The value of the contact angle hysteresis moved from 40∘ for flat PDMS to less than 10∘ for textured replicated surfaces. The wetting behavior of multiscale textured surfaces was then studied in the frame of the Wenzel and Cassie-Baxter models. Whereas the classical laws made it possible to describe the wetting behavior of the ginkgo biloba replications, a hierarchical model was developed to depict the wetting behavior of both bamboo species.

Multifunctional superhydrophobic surfaces

Surface wetting has a significant influence on the performance and applications of the materials. The superhydrophobic surfaces have water repellency due to low surface energy chemistry and micro/nanostructure roughness. The amazing applications of superhydrophobic surfaces (SHSs) lead to increase attention to superhydrophobicity in recent decades. The SHSs have been fabricated through chemical and physical methods. The further properties of SHSs as functions such as self-healing, anti-bacterial, anti-fouling, and stimuli-responsiveness are considered as the functions of the SHSs. The Multifunctional SHSs (MSHSs) that contained superhydrophobicity and at least two other properties as the next generation of the SHSs are swiftly developed in recent years. The multiple applications of the MSHSs are originated from specific morphology and functional groups of the MSHSs. The functions (properties) of the MSHSs are categorized into three groups including self-cleaning properties, restrictive properties, and smart properties. Designing and keeping surface structure plays a significant role in fabricating durable MSHSs. However, there is a big challenge to design and also scale up mechanochemical durable MSHSs. Based on state-of-the-art investigations, establishing a self-healing function can improve the durability of SHSs. The durable self-healing MSHSs can enhance the performance of the other functions and lifespan of the surface. In this review, all surface structures and superhydrophobic agents in MSHSs are investigated. The perspective of the MSHSs determined the next generation of the MSHSs have several significant parameters including durability, stability, more functions, more responsiveness, and environmentally friendly features for fabricating the large-scale MSHSs and enhancing their applications.

Contrasting Oxygen Reduction Reactions on Zero- and One-Dimensional Defects of MoS2 for Versatile Applications

Oxygen reduction reaction (ORR) is a key microscopic process in many electrochemical applications of materials, where the requirements of their ORR performances may vary strikingly, for example, during the uses of MoS₂ as an electrocatalyst and anticorrosion/lubricating coating in aqueous/humid environments, ORR should be activated and inhibited, respectively. To reveal a complete ORR profile of MoS₂, using first-principles calculations, we examine the stabilities of various possible zero-dimensional point defects on the surface and one-dimensional edge defects and comprehensively explore the ORR activities on pristine MoS₂ surface and those defects in acid/alkaline solutions. It is found that the ORRs on the pristine surface and surfaces with point defects always require large overpotentials (>1.0 V), indicating a defect-immune resistance of the planar MoS₂ surface against the ORR. However, the ORR overpotentials on edge defects can reach as low as 0.66 V, corresponding to a relatively high activity close to that of the prototypical catalyst Pt (overpotential ∼0.45 V). Such contrasting ORR behaviors of point and edge defects are also understood in depth by analyzing the underlying thermodynamic and electronic-structure mechanisms. This work not only quantitatively explains the performances of MoS₂ in both galvanic corrosion and electrochemical catalysis but also provides a useful structure-ORR map that can facilitate adapting the realistic MoS₂ to versatile electrochemical applications.

Enhancing the Robustness of Superhydrophobic Coatings via the Addition of Sulfide

Micro/nano hierarchical structures with special wettability impart a wide spectrum of unique properties to the superhydrophobic surfaces that are applicable in different potential fields. Therefore, it is necessary to develop advanced superhydrophobic materials with excellent wear-resistance properties. In this study, PDMS-based robust superhydrophobic coatings, which used MoS₂ or WS₂ as a solid lubricant, PDMS as a binder, and SiO₂ as a filler, were prepared on glass substrate by the one-step air spaying method. Lamellar MoS₂ and WS₂ with high crystallinity had intrinsic hydrophobic properties. The MoS₂@SiO₂-PDMS (MSP) and WS₂@SiO₂-PDMS (WSP) coatings with very rough textures showed good water-repellent behavior with water contact angles of 167.8 and 166.2°, respectively. The results demonstrated that the addition of microsized MoS₂ or WS₂ could easily format micro/nano second-level hierarchical structures, thus realizing the superhydrophobic properties. The friction coefficient decreased gradually with the increasing in MoS₂ or WS₂. A 4:1 ratio of SiO₂ to MoS₂/WS₂ could cause the samples to preserve their superhydrophobic properties even after 100 cycles on the abraser. As a result, superhydrophobic coatings with excellent wear resistance will be good candidates for water-repellent surfaces to meet practical emerging needs in industry applications.

Current and future envision on developing biosensors aided by 2D molybdenum disulfide (MoS2) productions

Two-dimensional (2D) layered nanomaterials have triggered an intensive interest due to the fascinating physiochemical properties with the exceptional physical, optical and electrical characteristics that transpired from the quantum size effect of their ultra-thin structure. Among the family of 2D nanomaterials, molybdenum disulfide (MoS₂) features distinct characteristics related to the existence of direct energy bandgap, which significantly lowers the leakage current and surpasses other 2D materials. In this overview, we expatiate the novel strategies to synthesize MoS₂ that cover techniques such as liquid exfoliation, chemical vapour deposition, mechanical exfoliation, hydrothermal reaction, and Van Der Waal epitaxial growth on the substrate. We extend the discussion on the recent progress in biosensing applications of the produced MoS₂, highlighting the important surface-to-volume of ultrathin MoS₂ structure, which enhances the overall performance of the devices. Further, envisioned the missing piece with the current MoS₂-based biosensors towards developing the future strategies.