The Synthesis of a Superhydrophobic and Thermal Stable Silica Coating via Sol-Gel Process

Biomimetic Superhydrophobic Surfaces by Nanoarchitectonics with Natural Sunflower Pollen

Superhydrophobic surfaces, known for their water-repellent, and self-cleaning properties, are widely used in various applications. These advanced functional surfaces exhibit high contact angles (>150°), achieved through low surface energy chemistries and hierarchical roughness. Natural sunflower pollen is micron-sized spherical particles with nano-sized spikes on the surface. This study engineered superhydrophobic coatings using the unique hierarchical structure of sunflower pollen and low surface energy additives like polydimethylsiloxane (PDMS) and silane additives such as 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FTS), octadecyltrichlorosilane (OTS) and dichlorodimethylsilane (DCDMS). The pollen content significantly modulates surface structure, roughness, and water contact angle. Higher pollen content enhances roughness and water repellency by creating micro-nano hierarchical structures. Pollen-PDMS-FTS and Pollen-PDMS coatings demonstrated the highest water contact angles (165 ± 2° and 163 ± 3°, respectively) and lowest sliding angles (4.5 ± 1° and 7.6 ± 2.6°, respectively), achieving a "lotus effect." Conversely, Pollen-PDMS-OTS or Pollen-PDMS-DCDMS coatings resulted in high sliding angles and water adhesion, producing a "rose petal effect." These "lotus effect" coatings are effectively applied in self-cleaning and water displacement in oil pipelines on hilly terrain. This study provides insights into the interplay between hierarchical structure and surface-free energy for designing superhydrophobic surfaces tailored for specific applications.

Factors Determining Unique Thermal Resistance and Surface Properties of Silicone-Containing Composites

This review discusses the key factors influencing the exceptional thermal resistance and surface properties of silicone-containing composites. Silicone polymers, known for their excellent chemical and physical properties, are widely used in a number of innovative products. In order to make silicone composites suitable for innovative applications, it is essential to ensure that they have both very good thermal resistance and superhydrophobic properties. Identification of the key factors influencing these properties enables the use of these composites in coatings, electronics and photovoltaic panels. The discussion includes the role of organosilicon polymer structures and the incorporation of micro- and nanoadditives to enhance the performance of these materials. Different methods for the modification and production of silicone composites are analyzed, with an emphasis on achieving thermal stability and surface superhydrophobicity simultaneously. The review highlights the growing demand for silicone-based coatings due to technological advances and environmental concerns. Furthermore, the role of surface modification and hierarchical surface structures in achieving these unique properties is discussed, as well as the potential applications and challenges in the development of next-generation silicone-containing materials.

Mechanisms of Hydrophobic Recovery of Poly(dimethylsiloxane) Elastomers after Plasma/Corona Treatments: A Minireview

Plasma/corona treatment could alter the wettability of a poly(dimethylsiloxane) (PDMS) surface from being hydrophobic to being hydrophilic, which has attracted many researchers' attention. However, the treated surface will gradually recover its hydrophobicity as it ages. To understand the recovery, many studies have been performed. Although there is still no general consensus on the recovery mechanisms, several models have been proposed that can explain the reported wetting behavior of hydrophobic recovery. In this minireview, we summarized the reported mechanisms underlying the hydrophobicity-recovery of oxidized PDMS surfaces, which are certainly affected by varied factors including temperature, aging time, stored conditions, and treatment conditions. We hope this minireview can give beginners in the field of microfluidics a better understanding on the various mechanisms that contribute to the hydrophobic recovery of PDMS surfaces and thus take appropriate measures to efficiently maintain the surface wettability of oxidized PDMS chips to prolong their performance.

Superhydrophobic cotton fabrics for effective removal of high-density polyethylene and polypropylene microplastics: Insights from surface and colloidal analysis

HYPOTHESIS

The use of superhydrophobic materials to remove particulate pollutants such as microplastics is still in its infancy. In a previous study, we investigated the effectiveness of three different types of superhydrophobic materials - coatings, powdered materials, and meshes - for removing microplastics. In this study, we will explain the removal process by considering microplastics as colloids and taking into account their wetting properties as well as those of a superhydrophobic surface. The process will be explained through the interactions of electrostatic forces, van der Waals forces, and the DLVO theory.

EXPERIMENTS

In order to replicate and verify the previous experimental findings on the removal of microplastics using superhydrophobic surfaces, we have modified non-woven cotton fabrics with polydimethylsiloxane. We then proceeded to remove high-density polyethylene and polypropylene microplastics from water by introducing oil at the microplastics-water interface, and we determined the removal efficiency of the modified cotton fabrics.

FINDINGS

After achieving a superhydrophobic non-woven cotton fabric (159 ± 1°), we confirmed its effectiveness in removing high-density polyethylene and polypropylene microplastics from water with a removal efficiency of 99%. Our findings suggest that the binding energy of microplastics increases and the Hamaker constant becomes positive when they are present in oil instead of water, leading to their aggregation. As a result, electrostatic interactions become negligible in the organic phase, and van der Waals interactions become more important. The use of the DLVO theory allowed us to confirm that solid pollutants can be easily removed from the oil using superhydrophobic materials.

Investigation of Electrochemical Assisted Deposition of Sol-Gel Silica Films for Long-Lasting Superhydrophobicity

Current methods for the protection of metal surfaces utilize harsh chemical processes, such as organic paint or electro-plating, which are not environment-friendly and require extensive waste treatments. In this study, a two-step approach consisting of electrochemical assisted deposition (EAD) of an aqueous silane solution and a dip coating of a low surface energy silane for obtaining a superhydrophobic self-cleaning surface for the enhanced protection of copper substrate is presented. A porous and hierarchical micro-nanostructured silica basecoat (sol-gel) was first formed by EAD of a methyltriethoxysilane (MTES) precursor solution on a copper substrate. Then, a superhydrophobic top-coat (E-MTES/PFOTS) was prepared with 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (PFOTS) for low surface energy. The superhydrophobic coating exhibited anti-stain properties against milk, cola, and oil, with contact angles of 151°, 151.5°, and 129°, respectively. The EAD deposition potential and duration were effective in controlling the microscopic morphology, surface roughness, and coating thickness. The E-MTES/PFOTS coatings exhibited chemical stability against acids, bases, and abrasion resistance by sandpaper. The proposed 2-layer coating system exhibited strong chemical bonding at the two interfaces and provided a brush-like surface morphology with long-lasting superhydrophobicity. The developed method would provide an environment-friendly and expedient process for uniform protective coatings on complex surfaces.

Removal of dyes, oils, alcohols, heavy metals and microplastics from water with superhydrophobic materials

A wide variety of pollutants can be currently found in water that are extremely difficult to remove due to their chemical composition and properties. A lot of effort has been made to tackle this issue that directly affects the environment. In this scenario, superhydrophobic surfaces, which have a water contact angle >150°, have emerged as an innovative technology that could be applied in different ways. Their environmental applications show promise in removing emerging pollutants from water. While the number of publications on superhydrophobic materials has remained largely unchanged since 2019, the number of articles on the environmental applications of superhydrophobic surfaces is still rising, corroborating the interest in this area. Herein, we briefly present the basis of superhydrophobicity and show the different materials that have been used to remove pollutants from water. We have identified five types of emerging pollutants that are efficiently removed by superhydrophobic materials: oils, microplastics, dyes, heavy metals, and ethanol. Finally, the future challenges of these applications are also discussed, considering the state of the art of the environmental applications of superhydrophobic materials.

Biology and nature: Bionic superhydrophobic surface and principle

Nature is the source of human design inspiration. In order to adapt to the environment better, creatures in nature have formed various morphological structures during billions of years of evolution, among which the superhydrophobic characteristics of some animal and plant surface structures have attracted wide attention. At present, the preparation methods of bionic superhydrophobic surface based on the microstructure of animal and plant body surface include vapor deposition, etching modification, sol-gel method, template method, electrostatic spinning method and electrostatic spraying method, etc., which have been used in medical care, military industry, shipping, textile and other fields. Based on nature, this paper expounds the development history of superhydrophobic principle, summarizes the structure and wettability of superhydrophobic surfaces in nature, and introduces the characteristics differences and applications of different superhydrophobic surfaces in detail. Finally, the challenge of bionic superhydrophobic surface is discussed, and the future development direction of this field is prospected.

Corrosion performance of a steel surface modified by a robust graphene-based superhydrophobic film with hierarchical roughness

Potentiostatic deposition of cobalt film and cobalt-graphene, Co-G, composite, followed by modification with low surface energy stearic acid (SA), was used to fabricate superhydrophobic films on a steel substrate successfully. A scanning electron microscope was used to analyze the surface morphology of the prepared superhydrophobic cobalt film modified by stearic acid, Co-SA, and the cobalt-graphene film modified by stearic acid, Co-G-SA. The findings show that both the fabricated films have micro-nanostructures. The Co-G-SA film shows a higher roughness due to the network structures of graphene and so exhibits higher superhydrophobicity. The Fourier transform infrared spectrophotometer, FTIR, results confirm the formation of Co-SA and Co-G-SA films on the steel surface. The wettability of the prepared films shows that they exhibit superhydrophobicity, where the Co-SA and Co-G-SA films have contact angles of 155° and 158°, respectively. The Potentiodynamic polarization results show that the value of the corrosion current density for steel coated with Co-SA (0.7094 µA) is lower than that of bare steel (0.1457 mA), while the coated steel with Co-G-SA film has the lowest value (0.1732 µA). The electrochemical impedance spectroscopy, EIS, results show that the charge transfer resistance for steel coated with Co-SA is 38 times that of bare steel, while steel coated with Co-SA is 57 times that of bare steel. Potentiodynamic polarization and EIS results show that the prepared Co-G-SA film superhydrophobic films exhibit higher corrosion resistance. Co-G-SA film has higher mechanical stability (maintains superhydrophobicity until 900 abrasion cycles), chemical stability (has superhydrophobicity in the pH range 1–13), and long-term stability (retains superhydrophobicity after 30 days in a 0.5 M NaCl solution) in 0.5 M NaCl solution.

λ/4–λ/4 Double-Layer Broadband Antireflective Coatings with Constant High Transmittance

Antireflective (AR) coatings can suppress the undesired interfacial Fresnel reflections, and they are widely used in optical devices and energy-related instruments. Conventional single-layer AR coatings, which only work at a single wavelength, encounter serious limitations in some practical applications because of their inherent properties. In this paper, λ/4–λ/4 double-layer antireflective (AR) coatings with constant high transmittance in a pre-determined wavelength range was prepared by the sol–gel method via acid-catalyzed and base-catalyzed SiO2 thin films. A double-layer antireflective coating with an almost constant transmittance value of 99.8% in the range of 550–700 nm was obtained, and the transmittance of this coating was higher than 99% in a wider range of 450–850 nm with a fluctuation of less than 1%. The coatings had good environmental stability and maintained constant high transmittance after two weeks of exposure in 50% humidity. The broadband AR coatings may have important applications in fields such as electroluminescent display.

Fabrication and Characterization of Hydrophobic Cellulose Nanofibrils/Silica Nanocomposites with Hexadecyltrimethoxysilane

Cellulose nanofibrils (CNFs) have attracted much attention because of their renewability and potential biocompatibility. However, CNFs are extremely hydrophilic due to the presence of a large number of hydroxyl groups, limiting their use as a water-resistant material. In this work, we controlled the adsorption behavior of silica nanoparticles on the surface of CNFs by adjusting the synthesis conditions. The silica nanoparticle size and packing efficiency on the CNF surface could be controlled by varying the ammonium hydroxide and water concentrations. In addition, hexadecyltrimethoxysilane (HDTMS) was successfully grafted onto CNF or CNF/silica nanocomposite surfaces, and the quantitative content of organic/inorganic substances in HDTMS was analyzed through XPS and TGA. The HDTMS-modified CNF/silica nanocomposites were more advantageous in terms of hydrophobicity than the HDTMS-modified CNF composites. This is because the silica nanoparticles were adsorbed on the surface of the CNFs, increasing the surface roughness and simultaneously increasing the amount of HDTMS. As a result, the HDTMS-modified CNFs showed a water contact angle (WCA) of ~80°, whereas HDTMS-modified CNF/silica nanocomposites obtained superhydrophobicity, with a WCA of up to ~159°. This study can provide a reference for the expansion of recyclable eco-friendly coating materials via the adsorption of silica nanoparticles and hydrophobic modification of CNF materials.

Ultrasonic assisted rapid preparation of superhydrophobic stainless steel surface and its application in oil/water separation

The preparation of superhydrophobic (SH) surface on stainless steel by chemical etching method is challenging due to the good corrosion resistance of the material. In this work, SH surface with water contact angle (WCA) as high as 163.21° was accomplished on 304 stainless steel surface by a rapid ultrasonic-assisted chemical etching method within 7 min and a low-cost fluorine-free modification treatment. The mechanism of ultrasonic field on the etching process was explored by detecting the cavitation and oscillation energy in the reactor. It is the first time to found that the ultrasonic cavitation effect enhanced the etching process by both chemical and physical facilitation resulting in hierarchical lamellar micro-structures, "mountain-like" micro-structure clusters and "coral-reef-like" nano-scale structures on the surface. With the ultrasonic power increasing, the ultrasonic cavitation effect not only enhanced the superhydrophobicity of sample surface, but also improved the uniformity of surface wettability. The samples also showed excellent performance of oil/water separation for various organics (all separation efficiencies up to 96%) and remarkable mechanical stability.

Fabrication and Characterization of Hydrophobic Porous Metallic Membranes for High Temperature Applications

Hydrophobic porous metallic membranes can be integrated in a microreactor for in situ separation of steam at high temperatures. This study investigates the fabrication and characterization of hydrophobic coatings on metallic substrates. Two different coating methods were explored: (1) Plasma Enhanced—Chemical Vapor Deposition (PE-CVD) to form amorphous carbon silicon-doped a-C:H:Si:O thin films and (2) Direct Immersion in fluoroalkyl silane (FAS-13) solution using dip coating to form Self-Assembled Monolayers. The results on wettability as well as SEM images and EDS/WDS analyses indicate that the coated sintered stainless steel membranes are adequate as hydrophobic surfaces, maintaining the porosity of the substrate and withstanding high temperatures. Especially the FAS-13 coating shows very good resistance to temperatures higher than 250 °C. These findings are of special significance for the fabrication of porous metal membranes for separation of steam in high temperature applications.

Palladium oxide-decorated mesoporous silica on graphene oxide nanosheets as a heterogeneous catalyst for the synthesis of β-substituted indole derivatives

In this work, an efficient and facile strategy has been adopted for the stepwise synthesis of the RGO-MSiO2/PdO hybrid nanomaterial (HY-NM). Herein, a hybrid nanostructure of mesoporous silica over graphene oxide (GO) sheets has been developed followed by immobilizing palladium oxide nanoparticles (PdO NPs), and then it has been utilized for catalyzing a multicomponent reaction (MCR). To authenticate the successful synthesis of the HY-NM and successive immobilization of PdO NPs, various physicochemical characterization techniques were utilized such as SEM, EDAX, HR-TEM, HR-XRD, TGA, BET, FT-IR, and XPS analysis. The activity of the HY-NM has been determined by performing the catalyst-mediated synthesis of β-substituted indole derivatives (yield 90-98%). The excellent catalytic activity of the prepared HY-NM could be observed due to its high surface area and large porosity, which facilitates the penetration and interaction of reactant molecules with the catalytic active species. This protocol eliminates the requirement of further purification after the isolation of the product from the reaction mixture. The ease of handling, recyclability of the catalyst, and simple work-up procedure are the main features of this protocol. The synthesized HY-NM could be recycled for multiple catalytic cycles making it a very effective heterogeneous catalyst.

The effects of bio-inspired micro/nano scale structures on anti-icing properties

Ice formation and accumulation have detrimental effects on commercial surfaces and people's lives. The ice adhesion strength decreases with increasing surface hydrophobicity, and the superhydrophobicity of a surface can be constructed by a combination of low surface free energy and high surface roughness. Conversely, the characteristics of biological surfaces have aroused wide attention as a result of the superhydrophobicity of plants and animals, deriving from the synergistic effects of chemical compositions and multi-scale hierarchical structures. Therefore, inspired by bio-mimetic studies on biological surfaces, a lot of artificial bio-inspired superhydrophobic surfaces have been broadly designed and constructed. Herein, we aim to summarize the fundamental theories of surface wettability and recent progress in the fabrication of bio-inspired surfaces. The bio-inspired surfaces prepared by different facile methods not only have superhydrophobicity, but also have anti-icing/icephobic properties. In the end, some challenges and problems in the future study and advancement of bio-inspired superhydrophobic surfaces are proposed.