Bilayer Coatings Research Articles

Bilayer coatings for extension of the shelf life of fish fillets: Incorporating seaweed sulfated polysaccharides in chitosan-alginate LbL structures.

The aim of this study was to develop a new active coating of layer-by-layer (LbL) structure composed of alginate (as polyanions) and chitosan (as a polycation) containing sulfated polysaccharide (fucoidan) from Sargassum angustifolium, to protect rainbow trout fillets during refrigerated storage. Chitosan and alginate do not combine with each other as a homogeneous solution, so they are suitable for multilayer coatings. The results demonstrated that coating samples with chitosan and fucoidan significantly improved the quality of fish fillets and extended their shelf life from 6 to 16 days. The chemical values (TBARS and TVB-N) and bacterial growth (total viable count (TVC), total psychrophilic count (PTC), and lactic acid bacteria (LAB)) indicated lower levels in the LbL coating samples containing fucoidan compared to the alginate and control samples. Among the different coating samples, the LbL coating with fucoidan (AChF1) exhibited lower weight loss, improved chromaticity (L*, a*, and b*), and minimal changes in mechanical and sensory evaluations. Based on the findings, AChF1 was the most effective treatment for increasing the shelf life of rainbow trout fillets during refrigerated storage. Therefore, it has potential applications in the food packaging industry.

Bilayer and trilayer X-ray mirror coatings containing W, Pt, or Ir<?oxy_insert_start author="CKapler" timestamp="20231211T162235-0500"?>,<?oxy_insert_end?> in combination with C, C/Co, B4C, or B4C/Ni: X-ray reflectance, film stress, and temporal stability

X-ray reflectance and film stress were measured for 12 bilayer and trilayer reflective interference coatings and compared with a single-layer Ir coating. The interference coatings comprise a base layer of W, Pt, or Ir, top layers of either C or B4C, and, in the case of the trilayer coatings, middle layers of either Co or Ni. The coatings were deposited by magnetron sputtering. Film stress was measured using the wafer curvature technique, while X-ray reflectance was measured at grazing incidence over the ∼0.1−10keV energy band using synchrotron radiation. Re-measurements over a period of more than two years of both stress and X-ray reflectance were used to assess temporal stability. The X-ray reflectance of all 12 bilayer and trilayer coatings was found to be both stable over time and substantially higher than single-layer Ir over much of the energy range investigated, particularly below ∼4keV, except near the B and C K-edges, and the Co and Ni L-edges, where we observe sharp, narrow drops in reflectance due to photo-absorption in layers containing these materials. Film stress was found to be substantially smaller than single-layer Ir in all cases as well; however, film stress was also found to change over time for all coatings (including the single-layer Ir coating). The effective area of future X-ray telescopes will be substantially higher if these high reflectance bilayer and/or trilayer coatings are used in place of single-layer coatings. Additionally, the smaller film stresses found in the bilayer and trilayer coatings relative to single-layer Ir will reduce coating-stress-driven mirror deformations. Nevertheless, as all the interference films studied here have stresses that are far from zero (albeit smaller than that of single-layer Ir), methods to mitigate such deformations must be developed in order to construct high-angular-resolution telescopes using thin mirror segments. Furthermore, unless film stress can be sufficiently stabilized over time, perhaps through thermal annealing, any such mitigation methods must also account for the temporal instability of film stress that was found in all coatings investigated here.

The effect of ceramic YSZ powder morphology on coating performance for industrial TBCs

The increasing turbine inlet temperatures in modern gas turbines have raised concerns about the corrosion of ceramic thermal barrier coatings (TBCs) caused by molten silicate deposits, commonly referred to as “CMAS” due to their main constituents (CaO-MgO-Al2O3-SiO2). The objective of this study was to investigate the combined influence of powder morphology and chemical composition on the CMAS resistance and thermal cycling resistance of ceramic monolayer and bi-layer coatings created through Atmospheric Plasma Spraying (APS). Three powder morphologies were examined: porous Agglomerated and Sintered (A&S) granules, Hollow Spherical (HOSP) powders, and dense, irregular Fused and Crushed (F&C) particles. Monolayer 7-8YSZ coatings with both porous and dense vertically cracked (DVC) microstructures, and bi-layer coatings consisting of a bottom layer of porous standard 7-8YSZ and a top layer composed of a porous high‑yttrium ZrO2–55 wt% Y2O3 were obtained using all three powder types (A&S, HOSP, or F&C). Furthermore, the bi-layer systems were deposited with different ratios between the individual layer thicknesses and/or different total thickness. FEG-SEM, EDX, and micro-Raman analyses, were conducted to assess the coatings' performance. Nanoindentation high-speed mapping and pillar splitting test were performed to evaluate the mechanical behaviour. The study on 8YSZ monolayers shows that coatings from a F&C feedstock exhibit higher density, reducing the CMAS penetration. However, these coatings demonstrate poorer thermal cycling performance due to increased stiffness and thermal stresses. Coatings from HOSP and A&S powders allow CMAS penetration but offer stress relief pathways, enhancing the coating's ability to withstand thermal stresses. Bi-layer coatings with a 55YSZ top coat show superior CMAS resistance compared to 7-8YSZ monolayer coatings, with limited penetration causing top coat peeling. The thickness ratio between the layers also affects thermal cycling resistance, where a thinner 55YSZ layer extends the TBC lifetime.

Stability and Failure Mechanisms of Al2O3|Al Bilayer Coatings Exposed to 300 Bar Hydrogen at 673 K

Hydrogen barrier coatings are important for future hydrogen economy to enable materials for applications in hydrogen tanks. In the present study, coatings consisting of amorphous Al2O3 (≈100 nm) synthesized by plasma ion‐assisted deposition on top of crystalline metallic Al (≈100 nm) are exposed to 300 bar hydrogen pressure at 673 K for 6 days. This is done to mimic and accelerate conditions in hydrogen storage containers for metallic hydrides. They remain intact after such harsh conditions, although changes do occur. Blister‐like features are observed consisting of a buckled oxide layer while the metallic Al layer underneath is retracted. As these features are also found for coatings annealed under 1 bar Ar atmosphere it is concluded that they are not related to the formation of gas bubbles but they form due to solid‐state dewetting. This is different to literature observation where H2 bubbles are reported as a consequence of interface diffusion of H/H+ species present due to the initial precursor used for film deposition. The mechanical properties of the coatings, which are evaluated from nanoindentation load–displacement curves, change only moderately. Overall, the study shows that Al2O3|Al coatings are suitable candidates to prevent hydrogen ingress, but dewetting due to long‐term exposure at elevated temperatures must be prevented.

Gelatin-mediated gallium-doped SrHA composite coatings with sequential antimicrobial and osteogenic functions for infected bone defect repair

In this study, gallium- and gelatin-modified strontium-doped hydroxyapatite (SrHA-Gel-Ga) bilayer coatings were prepared on titanium substrates by electrodeposition and spin-coating techniques. The results showed that gallium and gelatin were uniformly doped into the SrHA coatings, which exhibited good hydrophilicity and bioactivity. Furthermore, SrHA-Gel-Ga demonstrated good antimicrobial properties against E. coli and S. aureus, especially S. aureus. The co-doping of Sr and gelatin in the coatings was effective in mitigating the cytotoxicity of Ga. SrHA-Gel-Ga was better able to promote the adhesion, proliferation and early differentiation of MC3T3-E1 cells. This study provides a new strategy for the development of anti-infective bone repair coatings.

Effect of post-treated methods on corrosion resistance of MF-DC magnetron sputtering Al coating on TC4

PurposeThis study aims to investigate the effect of post-treatment on anti-corrosion performance of Al coating on the surface of Ti-6Al-4V (TC4) fastener.Design/methodology/approachThe Al coatings with different layer structures were prepared on TC4 by middle-frequency and direct-current combined magnetron sputtering. The cross-sectional morphology and surface roughness of coatings were characterized by scanning electron microscope and atomic force microscope. The corrosion resistance was evaluated by electrochemical method. The monolayer coating was post-treated by Alodine chemical conversion, Ar+ bombardment and a combination of two methods above.FindingsThe results show that the interfaces in bilayer and trilayer coatings reduce the defects. Ar+ bombardment reduces the corrosion current density, and Alodine chemical conversion leads to a higher pitting corrosion potential. The combined post-treatment has the highest polarization resistance.Originality/valueThe corrosion resistance of the Al coating is enhanced as the layer quantity increases. The combination of two post-treatments, Ar+ bombardment and Alodine chemical conversion, could achieve an overall improvement in corrosion resistance of Al coating.

Mechanical Characterization of Bi-Layer Environmental Barrier Coatings Under Tension and Bending Using Acoustic Emission and Digital Image Correlation

Abstract Fracture characteristics of bi-layer environmental barrier coatings (EBC) deposited on a woven ceramic matrix composite (CMC) substrate using air plasma spray processes were investigated under uni-axial tension and bend tests at room temperature. Health monitoring techniques such as acoustic emission (AE) and digital image correlation (DIC) were employed to better understand the cracking behavior of the coating and its progression. Post-test microscopy was performed to correlate the coating cracks with DIC and AE location. The results indicate that multiple transverse cracks first occurred in the coating, followed by substrate transverse cracks and additional coating cracks. DIC analysis was able to highlight the formation and location of these cracks. The fracture strength of the coating was estimated assuming the composite beam theory.

Ultra-hydrophobic biomimetic transparent bilayer thin film deposited by atmospheric pressure plasma

An open-air atmospheric pressure plasma was used to deposit ultrahydrophobic bilayer coatings. The plasma set-up was tuned, allowing the successive injection in the post-discharge of two monomers. To the best of our knowledge, no study describes the successive deposition by atmospheric plasma of two precursors, which could work in synergy and allow designing composite coatings of high added value. In this study, two liquid precursors were chosen for the deposition of single and bilayer coatings: (i) hexamethyldisiloxane (HMDSO) and (ii) 1H,1H,2H,2H-perfluorooctyltriethoxysilane (pFOTES). Single layer coatings (HMDSO and pFOTES) as well as bilayer coating (HMDSO/pFOTES) were analysed using multiscale techniques: Scanning Electron Microscopy (SEM), profilometer, Atomic Force Microscopy (AFM), Fourier-Transformed Infrared Spectroscopy (FTIR), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and drop shape analysis. The bilayer system (HMDSO/pFOTES), resulting from the successive deposition of HMDSO and pFOTES precursors, was confirmed by ToF-SIMS characterization while contact angle measurements highlighted the ultrahydrophobic property of the bilayer: water was fully repelled, with a zero contact angle hysteresis. This resulted from the combination of the multiscale roughnesses of the HMDSO-based and pFOTES based layers, combined with the intrinsic hydrophobicity of the pFOTES layer.

Electrochemical deposition of bilayer PPy/PPy-HA coating on AZ31 Mg alloy: Effect of HA content on characteristics and corrosion protection

This study aimed to examine the impact of naturally derived hydroxyapatite (HA) particles on the surface characteristics and corrosion behavior of polypyrrole (PPy)/polypyrrole-HA bilayer coatings. The coatings were applied onto AZ31 Mg alloy substrates using the potentiostatic electrodeposition method. Varying concentrations of HA particles (1, 3, and 5 wt%) were incorporated into the electrodeposition baths to create the top composite layers. Morphological analysis using FESEM revealed that the presence of HA particles led to PPy coatings with reduced porosity and more compact structures. EDS analysis and elemental mapping confirmed the presence of HA particles within the PPy matrix. AFM topography parameters indicated a slight increase in roughness values as the concentration of HA particles increased, with the average roughness rising from 46 nm for pure PPy coating to 53 nm for the coating with the highest HA content. Wettability results showed that the water contact angle (WCA) decreased from 56.6° for unreinforced PPy to 35.6° for the bilayer PPy/PPy-5 wt%HA coating. The corrosion behavior of the samples was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. It was observed that HA particles effectively reduced the corrosion current density (icorr), with the icorr of the optimal bilayer coating containing 3 wt% HA being 3.7 × 10−7 A cm−2, approximately two times lower than that of unreinforced PPy coating. Furthermore, the adhesion strength of the coatings was not affected by the inclusion of HA particles.

Colorful low-emissivity paints for space heating and cooling energy savings

Space heating and cooling consume ~13% of global energy every year. The development of advanced materials that promote energy savings in heating and cooling is gaining increasing attention. To thermally isolate the space of concern and minimize the heat exchange with the outside environment has been recognized as one effective solution. To this end, here, we develop a universal category of colorful low-emissivity paints to form bilayer coatings consisting of an infrared (IR)-reflective bottom layer and an IR-transparent top layer in colors. The colorful visual appearance ensures the aesthetical effect comparable to conventional paints. High mid-infrared reflectance (up to ~80%) is achieved, which is more than 10 times as conventional paints in the same colors, efficiently reducing both heat gain and loss from/to the outside environment. The high near-IR reflectance also benefits reducing solar heat gain in hot days. The advantageous features of these paints strike a balance between energy savings and penalties for heating and cooling throughout the year, providing a comprehensive year-round energy-saving solution adaptable to a wide variety of climatic zones. Taking a typical midrise apartment building as an example, the application of our colorful low-emissivity paints can realize positive heating, ventilation, and air conditioning energy saving, up to 27.24 MJ/m2/y (corresponding to the 7.4% saving ratio). Moreover, the versatility of the paint, along with its applicability to diverse surfaces of various shapes and materials, makes the paints extensively useful in a range of scenarios, including building envelopes, transportation, and storage.

Effect of functionalized hybrid chitosan/gum Arabic bilayer coatings with lemongrass essential oil on the postharvest disease control and the physicochemical properties of papaya (Carica papaya) fruits

The aim of this investigation was to determine the antifungal efficacy of Lemongrass Essential Oil (LGEO) against postharvest pathogens - Lasiodiplodia theobromae and Rhizopus stolonifer and to estimate the combined effect of Chitosan (CH) and Gum Arabic (GA) bilayer coatings on the physicochemical properties of the papaya fruit during its postharvest storage. Papaya fruits were coated by immersion in a solution of CH (1%), LGEO (0.05%) and GA (10%) for 5 min and stored at 25 ± 2 °C. In vitro, the LGEO exhibited antifungal activity at 8 µL/Petri-dish by inhibiting mycelial growth. In vivo, the lowest disease incidence and severity of L. theobromae and R. stolonifer were obtained for the fruits treated with CH/LGEO (533.3 µL/L) and GA. Furthermore, the treatment also provided excellent postharvest shelf-life to the fruits for ∼13 d at 25 ± 2 °C. Essential oil functionalized bilayer coating could be the best alternative technique to extend the postharvest shelf-life of papaya fruits.

Mono and bilayer coatings of alkanethiol and silane on copper: Prevents corrosion and regulate bacterial adhesion

Self-assembling molecules (SAMs) provide a flexible system for surface modification of materials by forming films of molecular thickness. SAMs protect materials from corrosion and modify surface properties such as adhesion, adsorption and wetting due to their molecular composition and orientation. In this investigation, polished copper specimens were dip coated to form SAMs of alkanethiol and silane to study bacterial adhesion as well as for corrosion prevention. The SAM coated specimens were exposed to the log phase cultures of Pseudomonas aeruginosa (aerobic bacteria) and Desulfovibrio vulgaris (anaerobic bacteria) for 12, 24 and 48 hrs, to monitor cell adhesion and biofilm thickness by microscopy. The results showed that alkanethiols SAM promoted adhesion and biofilm formation. The biofilm thickness ranged from 10 to 38 µm for Pseudomonas and 9 – 25 µm for Desulfovibrio sp. Among the SAM coatings tested, octadecyl-trichlorosilane (ODTCS), alkane-thiol and ODTCS (bilayer SAM) showed no bacterial adhesion, however, solitary alkane-thiol SAM showed significant bacterial adhesion. The high hydrophobicity (contact angle ∼140°), antibacterial and anti-biofilm property of the ODTCS coating could have regulated bacterial adhesion. The constant climate test results showed that silane SAM prevented copper corrosion up to ∼160 days (3480 hrs), while the alkanethiol coating could protect up to 10 days (240 hrs). Confocal laser scanning microscopic images of the silane coated copper specimens showed initiation of the corrosion after 160 days of exposure, while at the end of 200 days significant copper corrosion was observed. Surface modification leads to specific biochemical interactions that regulate bacterial adhesion and prevent biofilm formation and corrosion of copper.

Integrated MOF-74 Coatings on Magnesium for Corrosion Control, Cytocompatibility, and Antibacterial Properties.

Biodegradable Mg and its alloys can degrade safely in vivo without toxicity. The major bottleneck inhibiting their clinical use is the high corrosion rate, which leads to the loss of mechanical integrity prematurely and bad biocompatibility. One ideal strategy is the modification with anticorrosive and bioactive coatings. Numerous metal-organic framework (MOF) membranes show satisfactory anticorrosion performance and biocompatibility. In this study, MOF-74 membranes are prepared on an NH4TiOF3 (NTiF) layer-modified Mg matrix, fabricating integrated bilayer coatings (MOF-74/NTiF) for corrosion control, cytocompatibility, and antibacterial properties. The inner NTiF layer serves as the primary protection for the Mg matrix and a stable surface for the growth of MOF-74 membranes. The outer MOF-74 membranes further enhance corrosion protection, whose crystals and thicknesses can be adjusted for different protective effects. Owing to superhydrophilic, micro-nanostructural, and nontoxic decomposition products, MOF-74 membranes significantly promote cell adhesion and proliferation, showing excellent cytocompatibility. Utilizing the decomposition of MOF-74 to generate the products of Zn2+ and 2,5-dihydroxyterephthalic acid can effectively inhibit Escherichia coli and Staphylococcus aureus, displaying highly efficient antibacterial properties. The research may shed valuable strategies for MOF-based functional coatings in the applications of biomedicine fields.

Vacuum annealing effects on the microstructure and properties of HfO2-based bilayer antireflective coatings by magnetron sputtering

Hafnia (HfO2) retains thermal stability, mechanical resilience, and chemical resistivity, which makes it feasible in various high-tech applications in optics and integrated circuit technology. This work presents the effects of thermal annealing on the microstructure, optical performance, and wettability of HfO2/Al2O3 and HfO2/ZrO2 bilayer thin films prepared by magnetron sputtering. The films were deposited on silicon (Si) and glass substrates and then annealed at a certain temperature (300–500 °C) in the ambient vacuum condition for 5hrs. XRD results of as-deposited and annealed films revealed the polycrystalline nature of the monoclinic phase. The core level orbitals of Hf 4f, Zr 3d, and Al 2p spectra showed the formation of stoichiometric compositions of HfO2, ZrO2, and Al2O3 films and exhibited a slight shift in binding energy after annealing. The AFM and SEM analysis were utilized to inspect the roughness and surface morphology and correlated with the change in hydrophobicity to the self-cleaning nature of the prepared bilayer coatings. The observed upsurge in refractive indexes of the coatings is allied to the packing density that causes lattice contraction and enhances the attraction between dipoles. The negligible effect of negative temperature on the antireflection efficiency makes it suitable for future applications in optoelectronic, photovoltaic devices operated in a cold or humid environment.

Bilayer Coating Composed of Starch and Methyl Cellulose-Nanoscale TiO2 for the Protection of Historic Paper from UV

Among the agents of deterioration considered particularly damaging to cultural heritage objects are light, ultraviolet (UV) and infrared. The high-energy UV is the most damaging of the three, as it can cause irreversible visual, chemical and structural changes in cellulose-based materials. Known for its photocatalytic properties, TiO2 can absorb UV and is thermally and chemically stable. In this study, we propose an innovative bilayer coating composed of starch, methyl cellulose and nano-TiO2 to utilize UV blocking properties of TiO2. The results of the treatments were assessed by determining physical, optical and surface properties, as well as the degradation degree of the samples, prior and post accelerated ageing. The results show that an increase in the weight concentration of TiO2 enhances the colour difference, but the colour of samples coated by lower concentrations of TiO2 after accelerated ageing is closer to the original value than the colour of the uncoated ones. An increase in both the contact angle and the absorption time is also present, but after ageing, both parameters significantly decrease due to the presence of TiO2. To conclude, the presented nanocomposite coating can protect historic paper from UV, but one should bear in mind that a higher weight concentration could lead to a higher water sensitivity after exposure to UV.

Polymer bilayer-Micro arc oxidation surface coating on pure magnesium for bone implantation.

Pure magnesium-based ortho-implants have a number of advantages. However, vital parameters like degradation rate and biocompatibility still call for significant improvement. In this study, poly (1,3-trimethylene carbonate) (PTMC) and polydopamine (PDA) bilayer and micro arc oxidation composite coatings were prepared successively on magnesium surface by immersion method and microarc oxidation. Its corrosion resistance and biocompatibility were evaluated by in vitro corrosion tests, cellular compatibility experiments, and in vivo animal experiments. In vitro experiments demonstrated that the composite coating provides excellent corrosion protection and biocompatibility. Animal studies demonstrated that the composite coating slowed the degradation of the implant and was not toxic to animal viscera. In conclusion, the inorganic-organic composite coating proposed in this study provided good corrosion resistance and enhanced biocompatibility for pure magnesium implants. The translational potential of this article is to develop an anti-corrosion composite coating on a pure magnesium surface and to verify the viability of its use in animal models. It is hoped to open up a new approach to the design of new degradable orthopedic magnesium-based implants.

Oxidation behavior of CrAl-Mo coated Zircaloy-4 in DB and BDB scenarios

Cr coatings have been widely applied on Zircaloy for accident tolerant fuel materials. However, it has long been a great challenge in the nuclear community for Cr coatings surviving in the beyond design basis conditions (BDB) because of the unstable chromia layer and eutectic reactions between Cr and Zr. In this study, bi-layered CrAl-Mo coatings have been designed to improve the performance of Cr coatings in the BDB conditions. Results showed that the CrAl-Mo coated samples can tolerant in steam at temperatures as high as1400 °C because of the formation of a more stable alumina layer on the surface and the inhibition of eutectic reactions near the coating/substrate interface. Moreover, diffusion of Mo facilitated the formation of a CrAlMo layer, which stabilized the outer alumina layer and reserved the Al inventory within the coating.

Nanoscratch-healing of single and bilayer thin films of hindered urea bond-based self-healable copolymers

In this study, the effects of the surface properties of single and bilayer thin films of hindered urea bond (HUB)-based self-healable copolymers on their scratch-wound formation and self-healing were investigated. Initially, three prepolymers with bulky amine groups, PtB (control), PFtB (hydrophobic), and PMtB (hydrophilic), were synthesised by free-radical polymerisation. Subsequently, they were used to fabricate self-healing copolymers by crosslinking with HDI. The three crosslinked polymers (PtB-H, PFtB-H, and PMtB-H) showed contact angles of 80°, 93°, and 73°, respectively. Moreover, all the single-layer samples showed complete scratch healing within 2 h at ambient temperature, with PFtB-H and PMtB-H showing an initial elastic recovery immediately after scratch formation, unlike PtB-H. The formation of bilayer samples by stepwise coating was confirmed by X-ray photoelectron spectroscopy (XPS). Owing to HUB networks formed on their surface similar to the single-layer, bilayer coatings showed excellent scratch-healing performance at room temperature for nano-scratches with 40–50 nm depth, as indicated by AFM. PMtB-H@PtB-H showed a better scratch-healing performance than PFtB-H@PtB-H, and the scratch-healing ability of PMtB-H@PtB-H was improved by moisture. Their nano-scale self-healing ability was verified by micro-scale scratch tests; scratches with 4–12 µm depth healed completely with ∼100% SHE% at 60 °C.

Evaluation of adhesion strength, corrosion, and biological properties of the MWCNT/TiO2 coating intended for medical applications.

Multi-wall carbon nanotube (MWCNT) coatings are gaining increasing interest because of their special properties used in many science fields. The titania coatings are known for their improvement of osteoblast adhesion, thus changing the surface architecture. Bi-layer coatings comprising 0.25 wt% of the MWCNTs and 0.30 wt% of titania (anatase structure) were synthesized in a two-stage procedure using the electrophoretic deposition method (EPD). The MWCNT and TiO2 coatings were deposited with voltage and time parameters, respectively, of 20 V and 0.5 min, and 50 V and 4 min. EDS, AFM, SEM, Raman spectroscopy, nano-scratch test, potentiodynamic corrosion tests, wettability studies, and cytotoxicity determined with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test on human dermal fibroblasts (HDF) and mouse osteoblast precursors (MC3T3), and lactate dehydrogenase (LDH) activity test were carried out on examined surfaces. The prepared MWCNT/TiO2 coating is uniformly distributed by MWCNTs and agglomerated by TiO2 particles of size ranging from 0.1 to 3 μm. Raman spectroscopy confirmed the anatase structure of the TiO2 addition and showed typical peaks of the MWCNTs. The MWCNT/TiO2 coating had higher roughness, higher adhesion strength, and improved corrosion resistance compared to the MWCNT basic coating. The results of biological tests proved that physicochemical properties of the surface, such as high porosity and wettability of MWCNT/TiO2-coated material, would support cell adhesion, but toxic species could be released to the culture medium, thus resulting in a decrease in proliferation.

Effect of deposition sequence of MgAl-LDH and SiO2@PDMS layers on the corrosion resistance of robust superhydrophobic/self-healing multifunctional coatings on magnesium alloy

A multi-functional anti-corrosion coating integrating wear-resistant superhydrophobic(SH) and self-healing is expected to provide effective protection for magnesium alloys. In this work, the SiO2@PDMS (SP) coating and cysteine-intercalated MgAl-LDH (CL) are respectively chosen as the wear-resistant SH and the self-healing anti-corrosion coating, then two kinds of bilayer coatings with different deposition sequences: SP/CL and CL/SP were obtained accordingly. The morphologies, compositions, structures, superhydrophobic properties, wear-resistance, corrosion resistance and self-healing properties of these two coatings were investigated. SEM results show small SiO2 particles and large SiO2 particles intermingle to form a micro-nano structure on the SP/CL coating surface. While in the CL/SP coating, MgAl-Cys-LDH nanosheets are dispersed and grown in the gaps between SiO2 particles and on the surface of the magnesium substrate. Besides, their wear resistance is excellent, with the contact angles remaining at a high level (149.9° and 149.8°) after 50 cycles of sandpaper abrasion. Electrochemical tests indicate the corrosion resistance of CL/SP coating is better than that of SP/CL coating. It is mainly ascribed to the much denser CL/SP coating and the better adhesion between the SP and CL layers. A large number of CL nanosheets growing in the SP gaps can trap corrosion ions in time and effectively, significantly reducing the concentration of corrosion ions in the vicinity of the Mg surface. And the corrosion current density of CL/SP coating (Icorr=4.28×10−11 A/cm2) is 3 orders of magnitude lower than that of most of the related reports. Furthermore, the CL/SP coating shows a strong self-healing ability.