Hydrophobic Coatings Research Articles

Comparison and investigation of edible hydrophobic coatings on beeswax and carnauba wax oil gels

In our daily life, it often uses all kinds of liquid food, such as cola, fruit juice and other drinks. Whenever you finish using these, you will find that there will inevitably be residual liquid at the bottom of the bottle that cannot be poured out, resulting in a considerable waste. However, in recent years, the emergence of lubricant infused surface (LIS) can be used to solve this problem. In this research, LIS is prepared by forming an oleogel with shellac and linseed oil, which has the advantage that the experimental raw materials require low cost, the materials are easily available, and do not cause health hazards to human beings. To gain a deeper understanding of the mechanism of LIS antifouling, the effects of optimal Brazilian carnauba wax content and beeswax content on the surface morphology, water contact angle and sliding angle, chemical functional groups, transmittance, and oil-holding rate of LIS were investigated, and the effects of liquid foodstuffs antifouling were tested with optimal Brazilian carnauba wax and beeswax content, respectively.

Hydrophobic Coatings with Charge Permeability via Plasma Deposition of Long-Chain Perfluorocarbons.

Hydrophobization of nanotextured catalyst materials is a promising route to enhance the yield of N2 and CO2 conversion into green fuels. However, these applications require a hydrophobic coating to not only promote air trapping but also allow charge transfer at the electrode-electrolyte interface. In this work, nano thin films with thicknesses as low as 7 nm were deposited from the plasma phase of perfluorohexene, perfluorodecene, and perfluorooctane (PFO) precursors using a mild vacuum and gentle powers. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) characterization reveal that the resulting films are conformal and hydrophobic thanks to a good retention of CF2 and CF3 moieties. The PFO films exhibited the highest water contact angle and achieved superhydrophobic states when deposited on top of re-entrant nano features, an indication of successful air trapping. Electrochemical studies further demonstrated that the plasma-deposited PFO films allow charge transfer but could only sustain repeated cyclic voltammetry cycles without losing their hydrophobicity when deposited under optimal conditions. This result indicates that plasma deposition could become a viable route for the hydrophobization of electrocatalysts required to enhance the yield of poorly soluble gas reduction reactions.

How increasing cold spray coatings thickness affects their residual stress and properties

Cold spray (CS) is a solid state deposition presented in the literature to produce coatings for various applications, e.g., corrosion-resistant 316L stainless steel, Ti light alloy parts repairing, and hydrophobic Cu coatings. CS sprays particles under high velocity, impacting onto a prepared surface or substrate, and the powders bond by a severe and fast plastic deformation, consolidating the coating layer by layer. The number of layers depends on the designed coating thickness since each powder and CS parameters results in a different layer thickness. This work evaluates three feedstock powders (Cu, Ti, and 316L) for CS processing, and the characteristics and properties of the CS-ed coatings, studying the effects of the thickness coatings on their microstructure, porosity, hardness, adhesion to the substrate, and residual stress generated. The images of microstructures were obtained by optical microscopy and SEM, and the near-to-surface residual stress was measured by X-ray diffraction (XRD). Increasing the coating thickness produced a substrate deformation due to the compressive residual stress dominating the coating, which is numerically obtained and proven by XRD. Besides that, increasing the coating thickness slight increased the deposition efficiency for Cu ant Ti, but went in the opposite way for 316L; reduced the coating adhesion to the substrate; and did not altered significantly the hardness.

Improving the Barrier and Mechanical Properties of Paper Used for Packing Applications with Renewable Hydrophobic Coatings Derived from Camelina Oil.

This study looked at using modified camelina oil to develop sustainable coatings that could replace those derived from petroleum-based materials for use in packaging and other industrial sectors. Solvent-free synthesis of maleic anhydride grafted camelina oil (MCO) was carried out at two different temperatures (200 and 230 °C) to obtain sustainable hydrophobic coating materials for paper substrates. Maleic anhydride grafting of camelina oil was confirmed with attenuated total reflectance-Fourier transform infrared and NMR spectroscopic techniques, and up to 16% grafting of maleic anhydride was achieved, as determined by the titration method. MCO, obtained at different reaction temperatures, was coated onto cellulosic paper and evaluated for its hydrophobicity, mechanical, oxygen, and water vapor barrier properties. Scanning electron microscopy indicated the homogeneous dispersion of coating material onto the paper substrate. MCO-coated papers (MCO-200C paper and MCO-230C paper) provided a water contact angle of above 90° which indicates that the modified oil was working as a hydrophobic coating. Water vapor permeability (WVP) testing of coated papers revealed a reduction in WVP of up to 94% in comparison to the uncoated paper. Moreover, an improved oxygen barrier property was also observed for paper coated with both types of MCO. Analysis of the mechanical properties showed a greater than 70% retention of tensile strength and up to a five-fold increase in elongation at break of coated versus uncoated papers. Overall, the results show that camelina oil, a renewable resource, can be modified to produce environmentally friendly hydrophobic coating materials with improved mechanical and water vapor barrier properties that can serve as a potential coating material in the packaging industry. The results of this research could find applications in the huge paper packaging industries, specially in food packaging.

Enhanced electrophoretic deposition of hydrophobic BiVO4 photocatalytic coatings using Cu2+ ions as stabilizing agent

In this work, we report the preparation of monoclinic bismuth vanadate (BiVO4) coatings through an electrophoretic deposition process (EPD) using Cu2+ ions as a charge-stabilizing agent. BiVO4 was prepared through a rapid coprecipitation route, yielding rounded nanoparticles with sizes smaller than 100 nm. The bismuth vanadate nanoparticles were dispersed in isopropyl alcohol for electrophoretic deposition onto aluminum plates using a constant applied voltage of 12 V for 30 min. The results have shown that the deposited amount of BiVO4 nanoparticles increases with the initial concentration of the Cu(NO3)2⋅5H2O additive. According to XPS analysis, EPD coatings exhibit the presence of metallic copper due to the reduction of Cu2+ ions on the BiVO4 during the electrophoretic deposition process. The photocatalytic properties of BiVO4 coatings were assessed in the degradation of the antibiotic tetracycline under simulated solar irradiation. The BiVO4 coating prepared with an initial concentration of 0.5 mM of Cu(NO3)2⋅5H2O exhibited the highest photocatalytic performance, achieving a degradation efficiency of approximately 92 % after 240 min of irradiation. Furthermore, the BiVO4 coatings displayed superhydrophobic properties, as determined by measuring static water contact angles.

In Situ Construction of a Hydrophobic Honeycomb-like Structured ZnMoO4 Coating Applied for Enhancing Zinc Anode Performance.

Aqueous zinc-ion batteries (AZIBs) suffer from sharp cycling deterioration due to serious interfacial side reactions and corrosion problems on the zinc anode. Herein, an efficacious approach to construct hydrophobic ZnMoO4 coatings on Zn (denoted as Zn@ZMO) is proposed to mitigate direct contact between the zinc anode and electrolyte and enhance its cycle life. The hydrophobic ZnMoO4 layer (contact angle = 128°) with a honeycomb-like structure is prepared by an in situ liquid phase deposition method. The as-prepared ZnMoO4 coating exhibits persistent corrosion protection for Zn through 30 days of immersion in a 2 M ZnSO4 electrolyte, indicating excellent stability of the ZnMoO4 layer and ensuring its available application in AZIBs. Unique microchannels in this kind of honeycomb-like structured coating favor Zn2+ ion diffusion and ease of ion transport, especially at high current cycling. Its robust surface exclusion can effectively counter other side reactions induced by water, simultaneously. As a result, the Zn@ZMO symmetrical cell shows a remarkable cycle lifespan exceeding 2700 h at 1 mA cm-2/1 mA h cm-2, surpassing that of the bare zinc cell by more than 100 folds. At a current density of 5 A g-1, the Zn@ZMO//V2O5 cell can still achieve a specific capacity of 167.0 mA h g-1 after 500 cycles with a capacity retention rate of 88%, which demonstrates its long-term cycling stability.

Hydrophobic Coating of Vegetable-Tanned Leather with Dodecylamine

Vegetable-tanned leather exhibits a hydrophilic character due to the abundance of hydroxyl groups (-OH). In this study, the surface of vegetable-tanned leather was modified to become hydrophobic. The leather was coated using dodecylamine (DDA) through the padding method in the finishing process. The concentration of DDA varied from 1%, 2%, 3%, and 4% to identify the optimum concentration. The coating process was assisted by an activator, either acid or base, to improve the adhesion of DDA to leather. Uncoated vegetable-tanned leather was used as a control. The success of coating was identified using FT-IR and SEM-EDX analysis. The hydrophobicity of leather was conducted through a water resistance test. The success of coating is shown by the increase in their weight and thickness. Absorption bands of alkyl and amino groups of DDA are observed in FT-IR spectra around 1450 cm-1 and 3400 cm-1, respectively. SEM micrographs show that coated leathers have flatter surfaces as a consequence of DDA attachment on the leather surface. The water resistance test proves that the use of DDA can improve the leather hydrophobicity and enhance the water absorption time by up to 4 times. The optimum water absorption time is obtained when using 2% DDA.

Impacts of Differentially Shaped Silver Nanoparticles with Increasingly Complex Hydrophobic Thiol Surface Coatings in Small-Scale Laboratory Microcosms.

We investigated the impacts of spherical and triangular-plate-shaped lipid-coated silver nanoparticles (AgNPs) designed to prevent surface oxidation and silver ion (Ag+) dissolution in a small-scale microcosm to examine the role of shape and surface functionalization on biological interactions. Exposures were conducted in microcosms consisting of algae, bacteria, crustaceans, and fish embryos. Each microcosm was exposed to one of five surface chemistries within each shape profile (at 0, 0.1, or 0.5 mg Ag/L) to investigate the role of shape and surface composition on organismal uptake and toxicity. The hybrid lipid-coated AgNPs did not result in any significant release of Ag+ and had the most significant toxicity to D. magna, the most sensitive species, although the bacterial population growth rate was reduced in all exposures. Despite AgNPs resulting in increasing algal growth over the experiment, we found no correlation between algal growth and the survival of D. magna, suggesting that the impacts of the AgNPs on bacterial survival influenced algal growth rates. No significant impacts on zebrafish embryos were noted in any exposure. Our results demonstrate that the size, shape, and surface chemistry of AgNPs can be engineered to achieve specific goals while mitigating nanoparticle risks.

UV-durable self-cleaning coatings for autonomous driving

A key technology to ensure the safety and accuracy of autonomous driving for future transportation is the cleanliness of the sensor surfaces for accurate signal reading. This study focuses on hydrophobic coatings with self-cleaning performances and UV durability, their possible degradation mechanism of static water contact angle (sWCA), and the effect of the hydrophobic surface on camera image quality. The UV-durable hydrophobic coatings are applied by a spray process followed by a thermal curing. The UV-durable hydrophobic coatings are evaluated on a vision camera under lab-simulated weathering conditions such as rain, mud, fog, and bugs, on samples as-prepared and after various hours of Weather-Ometer® weathering. The results indicate that the sWCA degradation of the UV-durable hydrophobic coatings during accelerated weathering is corresponding to the loss of fluorine (F) atomic percentage in the coatings, and the vision camera imaging quality improves significantly with the UV-durable hydrophobic coatings in comparison to an uncoated surface. The self-cleaning performances of the UV-durable hydrophobic coatings, as measured by two metrics using signal-to-noise ratio and modulation transfer function 50 loss (MTF50loss), linearly correlate with sWCA of the coatings. The UV-durable hydrophobic coatings on the sensor surface will significantly benefit autonomous driving specifically for accurate signal reading under inclement weather.

Experimental and theoretical insights on long-term corrosion protection performance of MXene Nanosheets decorated with graphene quantum dots in epoxy coatings

In this study, MXene nanosheets decorated with zero-dimensional graphene quantum dots and functionalized with 3-aminopropyltriethoxysilane (APTES-MXene@GQDs) are used as a nanofiller in epoxy coatings. The MXene@GQDs and APTES-MXene@GQDs are characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results prove that the GQDs with spherical size (≤ 10 nm) have covered the MXene nanosheets through creating C-O-Ti covalent bonds. The Si-O-C and Ti-O-Si bonds in the APTES-MXene@GQDs indicate that both MXene and GQDs have reacted with the APTES molecules. The results of electrochemical impedance spectroscopy reveal that the low-frequency impedance modulus of epoxy coatings loaded with 0.1 wt% APTES-MXene@GQDs is 4.4 × 109 and 6.4 × 108 Ω.cm2 after 1 day and 7 weeks of immersion in NaCl solution, respectively. Meanwhile, hydrophobic coatings with high adhesion strength are achieved by adding the modified nanofillers. Density Functional Theory calculations emphasize the potential of MXene@GQDs nanohybrids in corrosion protection. The COO covalent bond significantly bolsters stability, making it a strong contender. An efficient electron transfer, as revealed in charge transfer dynamics, reinforces the interactions. The presence of MXene reshapes the electronic landscape, facilitating robust charge transfer processes. Conversely, the systems lacking MXene exhibit less advantageous energy level placement.

Exploring the Effectiveness of Hydrophobic Glass Surface on Touch-Enabled Digital Device to Reduce Microbial Adhesion and Propagation

ABSTRACT This study investigates the effectiveness of hydrophobic glass surfaces in reducing microbial populations on touch-enabled digital devices. Hydrophobic coatings have been proposed as a potential solution to minimize microbial adhesion and growth on device surfaces. Here, we intended to investigate the effect of hydrophobic spray on microbial load. The results were quantitatively analyzed using microbiological techniques. the nonhydrophobic surface harbors gradual microbial buildup upon time, such as threefold increase from 2 to 4 h and fivefold increase to 6 h post initial sampling with 143.6 ± 33.89 cfu/ml increase up to 264.7 ± 28.53 cfu/ml, whereas the hydrophobic surface had an overall build-up from 16.6 ± 1.2 to 50.45 ± 11.12 cfu/ml with P < 0.0001 significance. This research provides valuable insights into the potential application of hydrophobic glass coatings to mitigate microbial contamination on touch-enabled digital devices, enhancing their hygienic properties and minimizing the risk of infectious disease transmission.

PTFE-based flame retardant coatings optimized by melamine polyphosphate/aluminum diethyl hypophosphite/anhydrous transparent powder through orthogonal experiment

Hence, a novel hydrophobic intumescent flame-retardant coating is prepared using melamine polyphosphate (MPP), aluminum diethylphosphinate (ADP), and anhydrous transparent powder (ATP) as intumescent flame retardants (IFR), doped with polytetrafluoroethylene emulsion (PTFE) for flame-retarding plywood. The IFR/PTFE coatings are prepared using the sol-gel method. Firstly, the cone results demonstrate a significant enhancement in the flame retardancy of IFR/PTFE coatings. The Total Heat Release (THR) is reduced from 35.71 MJ·m−2 to 16.07 MJ·m2, while the Flame Retardancy Index (FRI) increases from 1 to 32.52. Moreover, according to the 3D Jander model (n = 3), the activation energy (Eα) for the coating rises from 209.52 to 253.50 kJ·mol−1 in the range of 327 °C to 430 °C. The coating achieves a maximum water contact angle of 113°. Notably, the optimal formulation of IFR is explored through orthogonal experiments, and the further optimized formulation (MPP: 21.16 wt%, ADP: 5.05 wt%, ATP: 10.17 wt%) is predicted using regression analysis model based on the Design of Experiments (DOE) method. Generally, it explores a strategy for preparing efficient IFR/PTFE hydrophobic coatings with promising prospects.

Insights into the hydrophobic coating with integrated high-efficiency anti-corrosion, anti-biofouling and self-healing properties based on anti-bacterial nano LDH materials

In this work, a series of hydrophobic coatings based on the anti-bacterial nano-hydrotalcite (LDH) materials were successfully prepared in this work. Results indicate that the introduction of Ag and sodium pyrithione (SPT) can effectively increase the anti-bacterial performance of NiAlZn LDH. The designed Ag/NiAlZn LDH and Ag/NiAlZn LDH-SPT coatings not only possess high anti-corrosion performance but can effectively inhibit the adhesion of Pseudomonas aeruginosa and Chlorella vulgaris. The anti-biofouling efficiencies of Ag/NiAlZn LDH-SPT coating against P. aeruginosa and C. vulgaris are 98.5% and 98.2%. Ag/NiAlZn LDH-SPT coating possesses integrated high-efficiency anti-corrosion, anti-biofouling and self-healing properties and good mechanical performance.

Enhancing the Proton Exchange Membrane in Tubular Air-Cathode Microbial Fuel Cells through a Hydrophobic Polymer Coating on a Hydrogel.

The usage time of air-cathode microbial fuel cells (MFCs) is significantly influenced by the moisture content within the proton exchange membrane (PEM). Therefore, enhancing the water retention capability of the PEM by applying a hydrophobic polymer coating to its surface has extended the PEM's usage time by three times and increased MFCs' operational duration by 66%. Moreover, the hydrophobic nature of the polymer coating reduces contamination on the PEM and prevents anode liquid from permeating into the air cathode. Towards the end of MFC operation, the internal resistance of the MFC is reduced by 45%. The polymer coating effectively maintained the oxygen reduction reaction activity in the cathode. The polymer coating's ability to restrict oxygen transmembrane diffusion is demonstrated by experimental data showing a significant decrease in oxygen diffusion coefficient due to its presence. The degradation efficiency of the chemical oxygen demand from 16% to 35% increased by a factor of one.

Improved electro-destruction of bacterial biofilms by coating conductive surfaces with polymers

The formation of biofilm involves cell aggregation and adherence, enveloped by a self-produced extracellular matrix. In the medical domain, biofilm-associated infections pose significant challenges, especially concerning implants. This investigation focuses on enhancing electromediated bacterial biofilm eradication through polymer coatings on the anode. These coatings catalyze reactive oxygen species (ROS) generation or convert hydrophobic coatings to bactericidal hydrophilic polycations, detaching the biofilms that are predominantly polyanionic. The first approach employs a metallized polytetrathienylporphyrin layer with ROS catalytic capability, while the second involves an insoluble hydrophobic polyamide, which, upon oxidation, transforms into a bactericidal hydrolytically degradable polycation. Both approaches show promising efficacy in augmenting electromediated Staphylococcus aureus biofilm destruction.

Composite Hydrophobic Coatings with Progressive High Penetration through Chromatography: Protective Properties and Mechanisms

Composite Hydrophobic Coatings with Progressive High Penetration through Chromatography: Protective Properties and Mechanisms

Eco-friendly composites with specific functional properties

The development of sustainable hydrophobic composite coatings is of high interest for aircraft applications. Currently, the use of natural derived functionalized microparticles as filler to obtain hydrophobic epoxy-based coatings was not deeply investigated. In this scenario, a novel hydrophobic epoxy-based composite including waste hemp microparticles functionalized with silica layer, 3-aminopropyltriethoxysilane, polypropylene-graft-maleic anhydride and silanes (hexadecyltrimethoxysilane and 1H,1H,2H,2H- Perfluorocotyltriethoxysilane) is presented. The resulting coating was casted on typical aeronautical panel, based on carbon-fiber-reinforced polymers, to achieve an improved hydrophobicity and anti-icing property induced by functionalized hemp microparticles.The wettability and anti-icing property were investigated. Compared to unfilled epoxy resin, the obtained composite coating achieved a greater water contact angle of 30° and doubled increase in icing time. Despite the low content (2 wt.%) of hemp particles, DSC analysis displayed a relevant increase in Tg value, confirming an efficient interaction between the epoxy matrix and the functionalized hemp filler. AFM analysis proved how the presence of hemp filler leads to an increase in roughness due to the hierarchical structure formed by the long chains of silane molecules. The combination of silane activity and rough morphology allows the development of hemp composite coatings with enhanced hydrophobicity, anti-icing behavior and thermal stability for aircraft applications.

Soil water repellency along elevation gradients: The role of climate, land use and soil chemistry

The rate of water infiltration, surface runoff, and overland flow are all affected by soil water repellency (SWR), i.e., the reduced affinity for water caused by hydrophobic coatings on soil particles. SWR impacts water balance, which in turn affects ecosystem’s function and watersheds hydrology, but little is known about changes of these properties along elevation gradient. Here, we investigate variation in SWR along four elevation gradients in four Italian mountain peaks, encompassing different land use and vegetation types from Mediterranean to temperate and alpine ecosystems. A total of 240 soil samples were collected for 48 ecosystems, and SWR was determined using the molarity of an ethanol droplet test. Soil characteristics were assessed using texture, pH, organic matter content, and soil salinity. Climate data were obtained using WorldClim, and their relationship with SWR was examined. SWR showed a unimodal pattern along the four elevation levels and in all cases peaked at mid-elevations between 1000 and 2500 m a.s.l.. SWR was highest under coniferous and deciduous forests and lowest for arable and bare soil. Soil organic matter and pH were the main determinants of SWR, with a positive and negative correlation, respectively. As for climate, mean annual temperature showed a hump-shaped relationship with SWR. In detail, we found that soil was hydrophilic at the extremes of elevation gradient where mean annual temperatures are less than −3.4 °C for alpine bare soils and higher than 12.7 °C for arable soils. This study allowed us to show how land use, soil chemistry, and climate are related to SWR along an elevation gradient. Further research is needed to concretely evaluate the effect of SWR on erosion risk at the watershed scale in the context of climate change.

Sol-gel Chemistry Approaches for the Manufacturing of Innovative Functional Composites for the Aerospace Sector

Sol-Gel is a “bottom-up” synthesis method that enables the production of films, nano/microparticles, fibers, gels, and bulk materials, both glassy and crystalline. Sol-Gel chemistry can be a vital tool for solving problems in several industrial applications where nanotechnology is necessary to overcome constraints. Here, various examples involving silicate-based materials are discussed. Silicatic materials with a variety of morphologies and applications, e.g., monodisperse SiO2 particles ranging in size from a few nanometers to a micron, can be synthesized through hydrolysis and polycondensation reactions of silicon alkoxide precursors. Using an environmentally friendly electrospinning process, silica nanoparticles can be incorporated into polyvinylpyrrolidone (PVP) fibers to create novel, fire-resistant sound absorbers. Additionally, by employing hybrid techniques based on Sol-Gel, the flame retardance of nanocomposites made of silica and epoxy resin as well as epoxy-based composites including hemp, even cured with cycloaliphatic hardeners, can be enhanced. The development of novel materials beneficial for aviation applications, such as hydrophobic (potentially self-anti-icing) coatings, is a further proof of the effectiveness of Sol-Gel chemistry.

Hydrophobic and Transparent Tantalum Pentoxide-Based Coatings for Photovoltaic (PV) Solar Panels

Photovoltaic (PV) solar panels suffer from efficiency losses due to the accumulation of dust on their surface during operation, as well as the loss of transparency in the top glass. The efficiency can be increased when hydrophobic films are deposited on the top glass of the solar cells. The top glass of solar cells must have three characteristics: high transmittance in the 380–750 nm range, a band gap greater than 3.2 eV and a refractive index higher than 1.23. So, the films require the same characteristics. This work presents an increase in the contact angle (related to an increase in the hydrophobic character) when Ta2O5 is partially substituted with ZnO. The studied films, physically deposited on glass by e-gun technology, present a non-crystalline state in the form of the X-ray patterns shown. The films have a transmission of 75%–80% in the visible range. The morphology and roughness of the coatings were evaluated by atomic force microscopy. All films show the values of the Millipore water contact angle higher than 91 degrees, leading to the acquisition of hydrophobic properties on the surface. In comparison, the substrate is hydrophilic, with an average contact angle of 53.81 ± 2.16. The hydrophobic properties and self-cleaning ability make the films recommendable for application. The band gap of the coatings was calculated with the Tauc method, and they have values of 4.5–4.6 eV.