Bilayer Coatings Research Articles

Characterization and tribological performance of new epoxy coatings modified with sustainable ionic liquid-graphene nanolubricants

Graphene-based nanolubricants were prepared using the environmentally friendly 2-hydroxyethylammonium lactate (ML) ionic liquid. The Graphene-ML dispersion (MLG) and neat ML were added to Epoxy Resin (ER) in 5 and 10 wt% proportions to study the effect on the curing conditions by means of Differential Scanning Calorimetry (DSC) and oscillatory rheology. A nucleating effect was found for Graphene, while ML presented a plasticizing effect. These findings were confirmed by DSC and Dynamic-Mechanical Analysis (DMA) with a decrease on the mechanical properties and glass transition temperature. ML and MLG were evaluated as external lubricants of epoxy coatings, finding outstanding friction and wear prevention ability. One and two layer ER coatings were deposited on AISI 1015 steel disks. When used as internal lubricant, MLG is able to prevent surface damage on bi-layer ER coatings. Therefore, we provide a novel approach for the preparation of ER composites with environmentally friendly nanolubricants for applications under demanding conditions.

Visualisation of surface coating distribution patterns on modified CaCO3

In this work, the surface modification of calcite-type calcium carbonate using the anionic surfactant sodium stearate was studied. The optimal amount of surfactant and its distribution on the surface of calcium carbonate is of great significance to the actual production. Various techniques were used to characterize these important parameters such as Fourier-transform infrared spectroscopy (FTIR), water contact angle measurements, Raman Mapping visualizationimaging, Raman depth profiling, thermogravimetric analysis (TGA), and atomic force microscopy (AFM). The results of the Fourier Transform Infrared (FTIR) suggest the formation of a coating on the surface of the modified calcium carbonate. Water contact angle measurements, Raman Mapping visualizationimaging, and TGA indicate that the optimal initial dosage of sodium stearate required to form a monolayer coating is about 2 wt%. Here, the hydrophilic heads of the sodium stearate are arranged vertically on the calcium carbonate surface forming the monolayer. As the concentration of sodium stearate increases, the hydrophobic tails of the sodium stearate or calcium stearate connect each other, forming bilayer or multilayer coatings. Furthermore, the surface coating on calcium carbonate originates from the edge vertices and gradually spreads towards the central region as the amount of sodium stearate increases until complete coverage is achieved. Raman depth profiling and AFM visualization results suggest that the thickness of the monolayer coating is approximately 5.25 nm.

Revolutionizing ELISA: A one-step blocking approach using lipid bilayer coatings

Enzyme-linked immunosorbent assay (ELISA) is an essential technique for biomolecule detection in diagnostics and research, but traditional protocols are time-consuming and variable. Conventional blocking agents like bovine serum albumin (BSA) pose ethical issues and potential assay interference. This study presents a one-step lipid-blocking approach to simplify the ELISA procedure. Compared to conventional blockers, the Lipid Universal Coating Assembly (LUCA) antifouling blocker showed comparable sensitivity while significantly reducing processing time and steps. Furthermore, it showed improved co-blocking efficacy and signal intensity in conventional protocols when combined with minimal BSA concentrations. Stability tests under accelerated aging confirmed the robustness of the LUCA antifouling blocker. Additionally, it effectively facilitated antibody detection for COVID-19 antigens in direct ELISA and human IL-6 antigen in Sandwich ELISA, suggesting its versatile applicability. Taken together, our findings reveal that one-step lipid blocking not only streamlines the ELISA process but also maintains high sensitivity and specificity, providing an efficient, user-friendly, and environmentally friendly alternative to traditional ELISA blockers and a robust platform for rapid diagnostics.

Prediction of contact stress and wear analysis of nitrided and CAPVD coated AISI H11 steel under dry sliding conditions

In this study, AlTiN (monolayer) and CrN/AlTiN (bilayer) coatings are deposited on the surface of conventional heat-treated AISI H11 steel which is then nitrided by cathodic arc physical vapor deposition (CAPVD). Structural analyses of the coatings reveal that homogeneous, continuous, and defect-free coatings are obtained with a good adhesion on the diffusion layer of the substrate material. Considering the surface hardness, the CrN/AlTiN coating (1718 HV0.01) deposited on the surface of the heat-treated tool steel has a higher value than that of AlTiN coating (1658 HV0.01), and this hardness value is increased even more (1932 HV0.01) with the application of the nitriding process. With a contact model in which the ANSYS static structural module is operated, it is shown that CrN/AlTiN coating contributes to lower tensile stress distribution on the surface during indentation. Analysis has also revealed that bilayer coating, CrN/AlTiN, exhibits reduced deformation compared to monolayer coating, indicating enhanced mechanical strength under contact conditions. Additionally, nitriding is found to increase stress distribution, emphasizing its role in improving coating performance. It is determined that wear losses can be reduced by the high load carrying capacity provided by nitriding and the high surface hardness provided by CrN/AlTiN coating under dry friction test conditions performed against alumina as counterpart material at room temperature.

Systematic characterization and enhanced corrosion resistance of novel β-type Ti-30Zr-5Mo biomedical alloys with halloysite nanotubes (HNTs) and zirconia (ZrO2)-reinforced polylactic acid (PLA) matrix coatings

This study investigates synthesis, the in-vitro corrosion resistance and adhesion performance of PLA-based composite coatings reinforced with halloysite nanotubes (HNT) and zirconia (ZrO2) on beta-type Ti-30Zr-5Mo biomedical alloys. The coatings were synthesized using the sol-gel method and characterized for their surface morphology, chemical composition, and electrochemical properties. SEM analysis revealed the presence of micropores and cracks, particularly in HNT and HNT/ZrO2 bilayer coatings. XPS and Raman spectroscopy confirmed the successful integration of HNT and ZrO2 into the PLA matrix. The potentiodynamic polarization scans and electrochemical impedance spectroscopy (EIS) showed enhanced corrosion resistance for coatings containing HNT and ZrO2, with the HNT/ZrO2 bilayer demonstrating the best performance. Contact angle measurements indicated hydrophilic properties, crucial for bioactive surfaces. Overall, the study demonstrates that HNT and ZrO2 reinforcements in PLA coatings significantly improve the corrosion resistance and bioactivity of Ti-30Zr-5Mo alloys, making them promising candidates for biomedical applications. Details are compared and discussed in the text.

Preparation and characterization of carboxymethylated pullulan/butyric acid-modified chitosan active sustainable bi-layer coatings intended for packaging of cheese slices

Dependence of the food industry on conventional plastic and the generation of enormous amounts of food waste caused by microbiological spoilage have been imposed as inspiration for this work, to develop active sustainable packaging for sliced cheese using the bi-layer design. Pullulan was modified using a green approach to obtain a polyanionic character in the coating formulation. Chitosan, which has a cationic character in an acidic environment, has been modified using a butyric acid to obtain an amphiphilic character. The formed active bi-layer has demonstrated an improved barrier (decreased permeability for moisture vapor 72.2 and 77.7 times) and mechanical properties (increased tensile strength value up to 3.9 and 9.4 times) compared to the monolayer films. A novel approach to microbiological control of sliced cheese has been established, which implies a synergistic effect of Helichrysum italicum essential oil (EO) and corresponding hydrolate (HY) incorporated in separated layers. This design has ensured avoiding surfactants and preserving cheese's sensory properties, prolonging its shelf-life by 50 % at least. Improvements in cheese storage conditions using this packaging lie in the improved barrier, mechanical and antimicrobial properties, the order of lamination, and a good covering of the cheese surface by spraying.

Development of Chitosan/Mg−Zn−HAP/ZrO2 Bilayer Coating on Ti Alloy for Biomedical Applications

AbstractTitanium alloys (Ti−6Al−4V) are being used in many biomedical applications due to their unique properties of bioactivity, excellent mechanical properties, low toxicity, biocompatibility, and long‐term implant application for their satisfactory corrosion resistance. We have developed a new two‐step fabrication process of zirconium oxide (ZrO2) and Chitosan/Mg−Zn−HAP (Chitosan/M−HAP) bilayer layer coating on Ti alloy for biomedical applications. Flower‐structured bilayers were coated by the electrochemical deposition method. Electrochemically deposited bilayer‐coated Ti alloy specimens were characterized by various analytical techniques like field‐emission scanning electron microscope (FE‐SEM), X‐ray diffraction (XRD), and EDS mapping analysis. Furthermore, the developed bilayer (Chitosan/Mg−Zn−HAP/ZrO2) coated Ti alloy samples improved mechanical properties such as adhesion strength (20.1±0.4 MPa) and hardness (446±4 Hv), compared to other coatings. An investigation of polarization curves showed a positive shift in the polarization values (Ecorr, and Icorr) of the Chitosan/M−HAP/ZrO2 bilayer coatings on Ti alloy. Bilayer‐modified Ti alloy samples show good antimicrobial response toward Gram‐negative and Gram‐positive bacteria. Meanwhile, the cell viability and proliferation of the bilayer‐coated samples were evaluated and the exhibited result improved cell proliferation, and bioactivity compared to other coated materials. From the results, it can be evident that the developed Chitosan/Mg−Zn−HAP/ZrO2 bilayer‐coated Ti alloy could be a good potential candidate for biomedical applications.

Widening the Gamut of Structural Colors of Gold via Insulator–Metal Bilayer Coatings

Tuning the color of Au has been a longstanding problem in the luxury industry. Conventional approaches, involving Au alloying, compromise purity and demand distinct alloy compositions for each hue. This study demonstrates a lithography‐free method for generating structural colors on a gold surface by adjusting the thickness of titanium dioxide, a high‐index dielectric. While color tuneability is limited if TiO2 is coated directly on the Au surface, a range of vivid colors can be generated if a 50−100 nm thick AuAl2 underlayer is used. AuAl2, an accepted alloy for purple gold, broadens the color gamut, providing a protective coating without diminishing gold purity. The reflectance dip of the bilayer structure exhibits a significant red shift with increasing thickness of the TiO2 layer, allowing diverse colors by TiO2 insulator tuning. Simulation studies corroborate experimental results, affirming that coating a TiO2 layer on the AuAl2 underlayer yields a wide range of colors. This method, based on thin‐film interference, shows promise for widespread use, offering a broad spectrum of structural colors in an industry striving for diverse Au color representation.

Physicochemical Evaluation of Coated Ginger during Long-Term Storage: Impact of Chitosan and Beeswax Bilayer Coatings at Different Temperatures

Physicochemical Evaluation of Coated Ginger during Long-Term Storage: Impact of Chitosan and Beeswax Bilayer Coatings at Different Temperatures

Fluorescence‐Enabled Colored Bilayer Subambient Radiative Cooling Coatings

AbstractPassive daytime radiative cooling has emerged as a promising green technology for the thermal management of buildings, vehicles, textiles, and electronics. Typically, both high solar reflectance and high thermal emissivity are prerequisites to achieve sufficient daytime cooling. However, colored radiative cooling materials are facing the dilemma of introducing visible light absorption, leading to challenges in balancing cooling and aesthetic demands. Here, three colored bilayer radiative cooling coatings, each comprised of a white base layer and a colored top layer with fluorescence enhancement are fabricated. Three phosphors (Sr2Si5N8:Eu2+, Y3Al5O12:Ce3+, and (Ba,Sr)SiO4:Eu2+) are employed with respective photoluminescence quantum yields (PLQYs) of 81%, 95.8%, and 91.0% as the colored pigment in the top layer. To mitigate the contradiction between coloration and solar reflectance, SiO2 microspheres are introduced into the top layer and utilize their Mie‐resonance‐based multiple scattering to increase the photoluminescent (PL) properties of the phosphors, which jointly boosts the effective solar reflectance (ESR) of the top layer. As a result, the three bilayer coatings exhibit soft colors while achieving subambient cooling with temperature drops of up to 1.5 °C. This fluorescence‐enhancement strategy may pave the way for preparing highly efficient radiative cooling coatings with tunable colors.

Investigation of the Nitriding Effect on the Adhesion and Wear Behavior of CrN-, AlTiN-, and CrN/AlTiN-Coated X45CrMoV5-3-1 Tool Steel Formed Via Cathodic Arc Physical Vapor Deposition

Monolayer (CrN, AlTiN) and bilayer (CrN/AlTiN) coatings are formed on the surface of conventional heat-treated and gas-nitrided X45CrMoV5-3-1 tool steel via Cathodic Arc Physical Vapor Deposition (CAPVD), and the adhesion characteristics and room- and high-temperature wear behavior of the coatings are compared with those of the un-nitrided ones. Scratch tests on the coatings show that the bilayer coating exhibits better adhesion behavior compared to monolayer ones, and the adhesion is further increased in all coatings due to the high load carrying capacity of the diffusion layer formed by the nitriding process. Dry friction tests performed at room temperature reveal that, among ceramic-based coatings, the coating system with a high adhesion has the lowest specific wear rate (0.06 × 10−6 mm3/N·m), and not only the surface hardness but also the nitriding process is important for reducing this rate. Studies on wear surfaces indicate that the bilayer coating structure has a tendency to remove the surface over a longer period of time. Hot wear tests performed at a temperature (450 °C) corresponding to aluminum extrusion conditions show that high friction coefficient values (>1) are reached due to aluminum transfer from the counterpart material to the surface and failure develops through droplet delamination. Adhesion and tribological tests indicate that the best performance among the systems studied belongs to the steel–CrN/AlTiN system and this performance can be further increased via the nitriding process.

Enhancing wear and corrosion resistance of TiO2–Al2O3 hybrid coatings by the development of TiO2–Al2O3 bilayer film coatings

Sol-gel fabricated TiO2–Al2O3 bilayer coatings were deposited on 316L surfaces with several combinations of layers. Microstructural, corrosion, and wear features of the fabricated film coatings were examined compared to the TiO2–Al2O3 hybrid coating containing 65 % TiO2, which achieved the highest protection against corrosion and wear in the previous study. The electrochemical properties were determined through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests, whereas dry sliding tests were performed using an Al2O3 ball under 1 N. Regardless of the production parameters, rutile and α-Al2O3 phases were produced in all manufactured coatings with similar thicknesses. The coatings consisting of TiO2 at the top layers showed better anti-corrosive performance due to a dense, low-porosity, and continuous morphology of TiO2 nanoparticles, while the coatings containing Al2O3 at their top layers were determined to exhibit higher wear resistance. All bilayer film coatings increased the anti-corrosion and anti-wear performance of the hybrid coating.

Enhancing Drug Delivery Efficacy Through Bilayer Coating of Zirconium-Based Metal-Organic Frameworks: Sustained Release and Improved Chemical Stability and Cellular Uptake for Cancer Therapy.

The development of nanoparticle (NP)-based drug carriers has presented an exciting opportunity to address challenges in oncology. Among the 100,000 available possibilities, zirconium-based metal-organic frameworks (MOFs) have emerged as promising candidates in biomedical applications. Zr-MOFs can be easily synthesized as small-size NPs compatible with intravenous injection, whereas the ease of decorating their external surfaces with functional groups allows for targeted treatment. Despite these benefits, Zr-MOFs suffer degradation and aggregation in real, in vivo conditions, whereas the loaded drugs will suffer the burst effect-i.e., the fast release of drugs in less than 48 h. To tackle these issues, we developed a simple but effective bilayer coating strategy in a generic, two-step process. In this work, bilayer-coated MOF NU-901 remained well dispersed in biologically relevant fluids such as buffers and cell growth media. Additionally, the coating enhances the long-term stability of drug-loaded MOFs in water by simultaneously preventing sustained leakage of the drug and aggregation of the MOF particles. We evaluated our materials for the encapsulation and transport of pemetrexed, the standard-of-care chemotherapy in mesothelioma. The bilayer coating allowed for a slowed release of pemetrexed over 7 days, superior to the typical 48 h release found in bare MOFs. This slow release and the related performance were studied in vitro using both A549 lung cancer and 3T mesothelioma cells. Using high-resolution microscopy, we found the successful uptake of bilayer-coated MOFs by the cells with an accumulation in the lysosomes. The pemetrex-loaded NU-901 was indeed cytotoxic to 3T and A549 cancer cells. Finally, we demonstrated the general approach by extending the coating strategy using two additional lipids and four surfactants. This research highlights how a simple yet effective bilayer coating provides new insights into the design of promising MOF-based drug delivery systems.

Salicylic and tartaric ions co-doped polypyrrole to enhance the corrosion protection of polypyrrole/zinc bilayer coating on ZK60 magnesium alloy in Hank's solution

To enhance the corrosion protection of the polypyrrole/zinc (PPy/Zn) bilayer coating on biodegradable ZK60 magnesium alloy in Hank's solution at 37 °C, sodium salicylate (NaSA) in different concentrations (CNaSA, 0.5–4.0 mM) is selected as a co-doping reagent of tartrate anions (TA−), and an electropolymerization method that combines potentiostatic and galvanostatic synthesis is developed to prepare PPy(TA + SA)/Zn bilayer coatings. The co-doping of SA− suppresses the growth of PPy and notably increases its synthesis potential (Epoly) with increasing CNaSA. The co-doped PPy(TA + SA) films have a surface morphology and thickness similar to the PPy(TA) film. However, their chemical composition, structure, and adhesion strength change notably due to their varying growth conditions. In the long-term immersion test of PPy(TA + SA)/Zn/ZK60 samples, the PPy(TA + SA)/Zn coatings exhibit high stability, and the coating prepared with CNaSA = 1.0 mM has the most prolonged protection time (54 ± 1.5 d). As CNaSA increases, the co-doped PPy(TA + SA) film becomes heavily over-oxidized to produce more defects on PPy chains due to the high Epoly, ultimately decreasing the protection time to 40 ± 1.0 d. The corresponding mechanism involved is thoroughly discussed.

Effect of TiN thin films deposited by oblique angle sputter deposition on sol-gel coated TiO2 layers for photocatalytic applications

TiO2 monolayer and TiN/TiO2 bilayer coatings were deposited on soda-lime glass prepared by mixing two techniques, TiO2 was deposited by sol-gel dip-coating and TiN film was deposited by oblique angle deposition using reactive magnetron sputtering at α=45° Structural analysis showed typical peaks of TiO2 anatase phase and cubic (Na-Cl type) structure of TiN. Roughness value of 3 nm was obtained for the TiN/TiO2 bilayer film with a rise and elongated grains size. It was found that the optical band gap energy decreases after coupling the TiN sub-layer which is explained by the incorporation of N atoms into TiO2 structure. At constant UV irradiation time, the photo-degradation of methylene blue rate increased for TiN/TiO2 film by 4 % compared to TiO2 film.

One-Pot Construction of Articular Cartilage-Like Hydrogel Coating for Durable Aqueous Lubrication.

Articular cartilage has an appropriate multilayer structure and superior tribological properties and provides a structural paradigm for design of lubricating materials. However, mimicking articular cartilage traits on prosthetic materials with durable lubrication remains a huge challenge. Herein, an ingenious three-in-one strategy is developed for constructing an articular cartilage-like bilayerhydrogel coating on the surface of ultra-high molecular weight polyethylene (BH-UPE), which makes full use of conceptions of interfacial interlinking, high-entanglement crosslinking, and interface-modulated polymerization. The hydrogel coating is tightly interlinked with UPE substrate through hydrogel-UPE interchain entanglement and bonding. The hydrogel chains are highly entangled with each other to form a dense tough layer with negligible hysteresis for load-bearing by reducing the amounts of crosslinker and hydrophilic initiator to p.p.m. levels.Meanwhile, the polymerization of monomers in the top surface region is suppressed via interface-modulated polymerization, thus introducing a poroussurface for effective aqueous lubrication. As a result, BH-UPE exhibits an ultralow friction coefficient of 0.0048 during 10000 cycles under a load of 0.9MPa, demonstrating great potential as an advanced bearing material for disc prosthesis. This work may provide a new way to build stable bilayer coatings and have important implications for development of biological lubricating materials.

Effect of titanium interlayer configurations on residual stresses and performance of titanium/titanium nitride multilayer coatings

Multilayer coatings provide an effective measure to control and optimise of residual stresses, enhance coating adhesion, fracture toughness, wear and corrosion resistance of coating system. In this study, we designed and produced bi-layer and four-layer titanium/titanium nitride magnetron sputtered coating configurations by altering the position of the interlayer. The in-plane residual stresses in different coating configurations are measured by multiple peak grazing incidence X-ray diffraction techniques. Subsequently, the effect of different compressive residual stresses on adhesion, mechanical properties, wear and corrosion resistance of coatings are investigated. Results show that the position of interlayer in multilayer coating configuration has a great impact on relaxation of residual stresses. The residual stresses are relieved by 26% and 46% by lowering the position of titanium interlayer from 800 nm at the top to 1000 nm and 1200 nm, respectively. The nanoindentation hardness is decreased by 11% and 13%, respectively. The wear rate of multilayer coating having interlayer position at 800 and 1000 nm from the top is ≈ 23% lower compared to bilayer however it is increased by ≈ 50% when interlayer coatings position changed to 1200 nm from the top. The interposition of interlayer in multilayer coating configurations decreased the corrosion current density by ≈ 50%. All multilayer coatings including higher residual stresses show better adhesion to the substrate compared to bilayer coatings which shows severe delamination.

Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes.

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries.

Investigation of Cu-diamond/Cu-diamond-high-entropy alloys bi-layer coating via mechanical alloying

In this work, Cu-diamond/Cu-diamond-Cu2NiAlAgZn bi-layer coatings were prepared via mechanical alloying on copper substrate, in which Cu-diamond was the inner layer and Cu-diamond-Cu2NiAlAgZn was the outer layer. The results revealed that the quinary alloy Cu2NiAlAgZn HEAs has simple FCC solid solution structure and the interface of bi-layer coating is identifiable. The inner gray area consisted of a Cu-diamond composite, while the outer gray area was a Cu2NiAlAgZn HEAs reinforced Cu matrix composite. However, there were some defects in the microstructure and the compactness was not satisfactory. Therefore, recrystallization annealing treatment was performed on the bi-layer coatings. The microhardness distribution from the substrate to the coating showed the characteristics of ‘increase-drop-increase’ before and after heat treatment. Although the microhardness slightly decreased, heat treatment resulted in a denser coating and eliminated defects. Moreover, the thermal and electrical conductivity of the sample that have undergone heat treatment significantly increased.

Analyzing the corrosion and tribocorrosion performances of monolayer TiO2 and bilayer TiO2-SiO2 coatings at different SBF temperatures

In this study, monolayer TiO2 coating was formed by the anodization method and bilayer TiO2-SiO2 coating was formed by the spin-coating method on commercially pure titanium (Cp-Ti) samples. The aim of this work compare the effects of monolayer and bilayer coatings at 37 °C and 60 °C in simulated body fluid (SBF) on the corrosion and tribocorrosion behaviors of Cp-Ti material. XRD and SEM were used for structural characterization of the coatings. Afterward, the adhesion strength of monolayer and bilayer coatings was investigated. The bilayer film began to separate from the Cp-Ti surface at higher forces, which was associated with energy dissipation between the layers, increased load-carrying capacity, and increased surface hardness. The best resistance was achieved from the bilayer film in tribocorrosion experiment at both 37 °C and 60 °C SBF temperatures; the result was attributed to higher surface hardness and film thickness. Consequently, untreated, monolayer, and bilayer Cp-Ti samples were tested for adhesion strength, corrosion, and tribocorrosion and bilayer samples exhibited the highest performance.