Silica-based Hybrid Coatings Research Articles

Transparent thioether-ester-bridged polysilsesquioxane coating with enhanced water vapor barrier performance

Developing siloxane-based hybrid coatings with excellent water vapor barrier performance remains a great challenge. The water vapor barrier ability of siloxane-based coatings can be effectively improved by tailoring the chemical structure of silane precursors. In this article, three thioether-ester-bridged polysilsesquioxane (BPSQ) coatings were fabricated from bridged silsesquioxane precursors by sol-gel method involving hydrolysis and condensation reactions. The bridged silsesquioxane (BSQ) precursors were synthesized by (3-mercaptopropyl)trimethoxysilane (MPTMS) and reagents with molecular structure containing CC groups via a facile thiol-ene click reaction. Experimental evidence obtained from FT-IR and NMR techniques confirmed the bridged molecular structure of BSQ precursors. The results obtained from XRD, SEM and TEM proved that the BPSQ coatings had short range ordered and long range disordered lamellar structure parallel to the substrate. These lamellar BPSQ coatings performed better water vapor barrier ability with WVTR of 3 ~ 7 g·cm−2·d−1 in comparison to polymer and silica-based hybrid coatings. Of them, MA-BPSQ coating performed the best water vapor barrier ability. The chemical structure of bridged organic chain had great effect on the distance of lamellar nanostructure, which played a key role in improving water vapor barrier property of BPSQ coatings.

Influence of fluoroalkyl chains on structural, morphological, and optical properties of silica-based coatings on flexible substrate

The presented work aimed to investigate the dependence of the fluoroalkyl precursors, used in the sol–gel synthesis of silica-based materials, on the structural and optical properties of the final coating deposited on polyethylene terephthalate foil. The structural properties of the fabricated coatings were analyzed using Raman Spectroscopy, X-ray Photoelectron Spectroscopy, and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). The morphology of the samples was investigated using SEM and Atomic Force Microscopy methods. Optical properties were analyzed using ellipsometry and reflectometry. Additionally, the wettability properties with the surface free energy were determined. The cracks-free layers were obtained on the elastic substrate as proved by microscopic observations. The expected chemical structure was confirmed using spectroscopic studies that showed fluoroalkyl chains build into the final structure. The coatings (except the one obtained from the precursor with the longest fluoroalkyl chain) exhibited smooth surfaces and high transparency with a transmittance of 92% in the visible range. They had low refractive indices, which could be tuned in a wide range from 1.435 down to 1.347 (at 633 nm) by changing the fluorinated precursors and increasing the amount of fluorine in the material. A longer fluoroalkyl chain also improved the hydrophobic character of the coating. Such materials have great potential application in flexible photonic structures (for example in photovoltaics). Highlights, Influence of fluoroalkyl chains on structural, morphological, and optical properties of silica-based coatings on flexible substrate . • Fluorinated silica-based hybrid coatings deposited on polymeric foil were reported • The structural properties of the fabricated coatings were analyzed • The wettability properties with the surface free energy and optical properties were determined • The modification of properties depending on the content of fluorinated carbons was shown

Silica-based hybrids for adhesive coatings and their anti-salt damage in the protection of ancient sandstone

Hybrid coatings have been used as the protective materials on sandstone monuments for many decades. But the protective performance is strongly depended on the adhered interface between protective coating and matrix. To find out how the hybrid coatings affect the adhesive performances and anti-salt damage behaviors during Na2SO4 salt-loaded hygrothermal aging (SLHA) cycles, the surface/mechanical properties of three silica-based hybrid coatings (S1-S3) and their anti-salt damage results (surface weathering appearance, mass change, porosity, water absorption and morphology of pore structures) of the sandstones adhered by these hybrid coatings have been evaluated and discussed. The results reveal that dendritic Na2SO4 crystals cover on the sand grains in both natural and hydrophilic silica/PVA (S1) adhered sandstones, which makes the adhered sandstone perform the least damage. Owing to the high adhesive and mechanical strength, S1-adhered sandstones perform the best anti-salt damage during Na2SO4 SLHA cycles. While the needle-like and cumulate ellipsoidal Na2SO4 crystals precipitate in the pores and interstices result to much severe salt damaged in adhered sandstones by hydrophobic P(GMA-MAPOSS) (S2) and PGMA-g-P(MA-POSS) (S3) during Na2SO4 SLHA cycles, although they enhanced the strength of adhesive pore walls. Actually, the macro salt damage behaviors on the sandstones treated by different hybrid coatings are proved to be a competition result of different crystallization patterns. Therefore, the pore interface adjusted by protective coatings should be one of the decisive factors for anti-salt damage during the sandstone protection.

Optimized silica-based hybrid coatings for the protection of aluminum against chloride-rich environment

Sol–gel hybrid coatings have become one of the dominant platforms intended for anticorrosion applications. In this study, hybrid (silica/epoxy) ceramic coatings were designed and prepared using the sol–gel technique. 3-Glycidyloxypropyl trimethoxysilane and diglycidyl ether of bisphenol A (epoxy) were used as the main precursors, while 3-Aminopropyl triethoxysilane was involved as a coupling agent (linker) in different ratios along with diethylenetriamine as a tertiary hardener responsible for the hybrids curing. The formation of the silica as an inorganic network, epoxy as an organic network, and the interconnection between them was confirmed using FTIR. The scanning electron microscopy was utilized for investigating the morphology of the processed coatings. Moreover, the adhesion and the hardness of the formed coatings were evaluated as critical features for epoxy. Besides, thermogravimetric analysis was used to assess the thermal properties in order to overcome one of the disadvantages of epoxy coatings. Electrochemical Impedance Spectroscopy was performed in order to measure the capability of each combination for protection against corrosion. It was proven that the morphology of the product would vary in a great deal depending on the silica content, which plays a vital role in determining the mechanical and thermal properties of these coatings. Improvements could be witnessed by increasing the silica content up to a specific limit (ranging from 15 to 20%). However, a further increase in the silica content will lead to a noticeable drop in the corrosion resistance capability.

Anti-corrosion properties of oligoaniline modified silica hybrid coatings for low-carbon steel

Novel electroactive silica-based hybrid coatings were synthesized on the surface of Q235 low carbon steel via one-step electrodeposition and were analyzed by FTIR, UV-vis, SEM, OCA20 contact angle (CA) analyzer and CHI-660E electrochemical workstation, respectively. The CA test indicated, in comparison with bare Q235 substrate, the silica hybrid material modified by N, N'-Bis(4′-(3-triethoxysilylpropylureido)-phenyl)-1,4- quinonenediimine (TSUPQD) exhibited an excellent hydrophobic properties. More importantly, the deposition potential significantly affected the corrosion resistance of TSUPQD modified silica hybrid material. By comparing with various deposition potentials (−1.1, −1.3, −1.5, −1.7V) under the deposition time of 500s, the coating prepared under the potential of −1.5V presented the best anti-corrosion performance for Q235 steel in 3.5wt.% NaCl solution. The XRD and SEM analysis of corrosion product beneath the hybrid coatings showed that the redox catalytic capability of aniline trimer unit induced the Q235 substrate to form the passive films which mainly consisted of α-Fe2O3 and Fe3O4.

Anti-Corrosion Silica-Based Hybrid Coatings for the Protection of AA2024 Alloy

Anti-Corrosion Silica-Based Hybrid Coatings for the Protection of AA2024 Alloy

Anti-Corrosion Silica-Based Hybrid Coatings for the Protection of AA2024 Alloy

In this work, design and preparation of different hybrid ceramic coatings based on Diglycidyl ether of Bisphenol A (Epoxy) and 3-Glycidyloxypropyl trimethyloxysilane (GLYMO) by sol-gel technique was studied. The obtained hybrids coatings were cured by using different hardners. Microstructure assessment of the prepared hybrids was investigated using FTIR. The morphology of the hybrid (silica/epoxy) coatings has also been studied by scanning electron microscopy (SEM). Evaluation of selected mechanical properties (adhesion, and hardness) were performed. In addition, the thermal properties were investigated using thermogravimetric analysis (TGA). The investigation of the different prepared coatings for protection against corrosion were studied based on EIS measurements. The results showed that the silica content plays an important role in determining the morphology as well as the mechanical and thermal properties of the coatings. The EIS results showed an improvement in the corrosion resistance of the hybrid coatings with increasing the silica content up to a certain extent. However, further increase in the silica content, leads to a descent in the corrosion resistance.

Thermal properties of silica-based hybrids with different alkyl chains

The thermal properties of silica-based hybrid coatings containing alkyl chains of varying lengths were examined. The hybrid coatings with alkyl chains showed a higher thermal diffusivity than silica-only coatings. The thermal diffusivity increased with the mobility of the alkyl chains, which depended on their number of carbon in the alkyl chain. An Increasing the total number of alkyl chains led to improvements in the thermal properties of the coatings.

Corrosion protection of carbon steel by silica-based hybrid coatings containing cerium salts: Effect of silica nanoparticle content

One strategy for minimising corrosive attack on carbon steel involves the application of hybrid coatings rich in rare earths, on the basis of their low toxicity and environmental sustainability. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were each used here as precursors, together with various quantities of colloidal silica suspension, to improve barrier properties of the coatings. Ce(NO3)3·6H2O was added as a source of Ce(III) for further inhibition of corrosion. The corrosion resistance of each kind of sample was evaluated using potentiodynamic polarisation measurements and electrochemical impedance spectroscopy (EIS) in 0.35wt.% NaCl solution. The electrochemical behaviour at various immersion times was modelled by equivalent circuits to demonstrate the effect of silica nanoparticle loading on corrosion. Additional testing was performed under harsh conditions of salt spray chamber. The microstructure and composition of sol–gel coatings were characterised by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), focused-ion beam SEM/EDS analysis, X-ray photoelectron spectroscopy and confocal microscopy.

Solid State NMR and EIS Examination of SiO<sub>2</sub>-Epoxy Hybrid Coatings on Stainless Steel

Sol-gel SiO2 and hybrid films were deposited on 316L stainless steel by the dip process. Epoxy bisglycidyl hydroquinone (EBH) was used as an organic component in hybrid films. Both coatings were uniform and homogeneous and displayed good adhesion to the substrates. The thickness of hybrid coatings was greater than that of SiO2 coatings. Thermal condition preparation has significant influence on spectroscopic properties of samples. These features are due to changes of morphology of epoxy-silica hybrid compared to unmodified silica-gels and are related to decomposition at higher temperature. The corrosion behaviour of 316L stainless steel samples coated with SiO2 and hybrid films was studied in Ringer’s solution by electrochemical impedance spectroscopy. SiO2 and silica-based hybrid coatings produced by the sol-gel method offers a good protection against corrosion of stainless steel in Ringer’s solution. In contrast to the SiO2-coated samples and the hybrid coating heated to 200°C, the behaviour of the hybrid coating heated to 300°C changed from resistive to a barrier-like one during exposure to the solution. This change was found to be a transient effect only. During 1-month exposure to Ringer’s solution the coating lost its barrier properties.

A parametric study on processing of scratch resistant hybrid sol–gel silica coatings on polycarbonate

Scratch resistant silica-based hybrid coatings on polycarbonate substrates were formed by dip-coating of acid-catalyzed tetramethyl ortohosilicate (TMOS):diethylenetriamine (DETA):H2O:2-propanol sols. The sol formulation and dip-coating process parameters on microstructural and performance properties—here optical transmittance and scratch resistance—of the coatings were evaluated. The effect of water quantity, total aqueous component (H2O+2-propanol) amount and relative proportion of TMOS:DETA on film formation behavior and on performance properties have been investigated in a systematic way. It was found that an effectively polymerized hybrid coating rich in silica content, as realized for high TMOS or abundant water containing sols, resulted in defective films with microcracking and adhesion problems. High 2-propanol content on the other hand led to incomplete film coverage. It was shown that 5±1μm-thick, scratch resistant and pristine coatings exhibiting a visible transmittance of 86–88% can be formed with a single deposition process using an optimized sol formulation of TMOS:DETA:H2O:2-propanol of 30:30:20:20 in wt.%. Meanwhile, the hardness of the PC has increased from an initial value of 13.9±2 to 70±25 (Vickers hardness, HV1) upon coating. A surface hardness approaching to 250 HV1 can be attained by for the thicker coatings (8±1μm) deposited at higher withdrawal speeds. However, such films suffered from non-uniform coverage and poor surface/optical quality. The transmittance values reduced by a factor of 20–30% for thicker coatings.

Silica-based hybrid coatings for corrosion protection of carbon steel. Part I: Effect of pretreatment with phosphoric acid

This work studies the synthesis and characterization of hybrid organic–inorganic coatings based on silica to improve the corrosion resistance of carbon steel. Hybrid organic–inorganic silica sol–gel coatings were obtained by dipping in an organically modified silica sol synthesized through hydrolysis and condensation of 3-glicidoxipropyl-trimetoxisilano (GPTMS) and tetraethoxysilane (TEOS) in acidic catalysis. The coatings were doped with a cerium salt (Ce(NO3)3·6H2O) and loaded with silica nanoparticles in order to improve both barrier effect and the anticorrosive behavior of the coatings by the inhibitory effect of cerium. Prior to the application of the coating, some samples were treated with a phosphoric acid 2% v/v in order to improve coating adherence. A two layered coating was applied onto AISI 1010 carbon steel, the outer containing with a cerium salt and the inner one with silica nanoparticles without the cerium salt, producing homogeneous and cracks-free films. Raman spectroscopy was used to characterize the compounds present in the surface of steel after pretreatment with phosphoric acid. Microstructural characterization of coatings was performed by means of scanning electron microscopy (SEM).The evolution with time of the protective properties of films was studied by electrochemical impedance spectroscopy (EIS), providing quantitative information of the role of the pre-treatment. Electrochemical behavior in each stage of the corrosion processes was modeled by equivalent circuits. Additionally, films adhesion was evaluated by nano-scratch demonstrating that the phosphate treatment improves adhesion of the hybrid coating.

Silica-based hybrid coatings

Organosilica coatings obtained by the versatile sol–gel process are finding applications of great environmental and economic impact, such as in the case of new antifouling and anticorrosive paints entirely devoid of harmful effects. Whether as undoped ORMOSIL (organic modified silicates) or as doped silica/polymer composites, potent nanomaterials are obtained in which chemical and physical protection of the coated surfaces often accompany other functions. We investigate the principles behind this remarkable field of nanochemistry.

Sol-Gel-Derived Hybrid Coatings for Corrosion Protection

The corrosion resistance of sol-gel-derived, organic-inorganic, silica-based hybrid coatings was studied. Hybrid sols were prepared by copolymerizing tetraethylorthosilicate (TEOS) and 3-methacryloxypropyltrimethoxysilane (MPS) with a two-step acid-catalyst process. Hybrid coatings were dip-coated on 304 and 316 stainless steel substrates and annealed at 300°C for 30 minutes. The adhesion, flexibility, and biocompatibility of the coatings were examined. Hybrid coatings were found to be relatively dense, uniform and defect free. Electrochemical analyses showed that the coatings provided excellent corrosion protection by forming a physical barrier, which effectively separated the anode from the cathode. In addition, further experimental results revealed that the corrosion patterns are strongly dependent on the nature of the stainless steel substrates. Some possible mechanisms for corrosion breakdown associated with each type of substrate are also introduced.

Organic–inorganic hybrid coatings for corrosion protection

The corrosion resistance of sol–gel derived, organic–inorganic, silica-based hybrid coatings with various amounts of organic content was studied. Hybrid sols were prepared by copolymerizing tetraethylorthosilicate (TEOS) and 3-methacryloxypropyltrimethoxysilane (MPS) with a two-step acid-catalyst process. Hybrid coatings were dip-coated on 304 stainless steel substrates and annealed at 300 °C for 30 min. Such prepared hybrid coatings were found to be relatively dense, uniform and defect free. The adhesion and flexibility of the coatings were characterized. The influences of the amount of organic component incorporated into the coatings and the aging of sols on corrosion protection were studied. Electrochemical analyses showed that the relatively dense hybrid coatings provided excellent corrosion protection by forming a physical barrier, which effectively separated the anode from the cathode. Some preliminary biocompatibility tests were also conducted on the hybrid coatings.