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Organic-inorganic coatings based on polymethyl methacrylate (PMMA)–silica–lithium are an efficient alternative to protect metals against corrosion. Although the preparation methodology is established and the thin coatings (~10 µm) are highly protective, the use of an environmentally friendly solvent has not yet been addressed. In this work, PMMA–silica coatings were synthesized using 2-propanol as a solvent and deposited on aluminum alloy AA7075, widely used in the aeronautical industry. Different concentrations of lithium carbonate (0–4000 ppm) were incorporated into the hybrid matrix to study the structural and inhibitive effects of Li+ in terms of barrier efficiency of the coatings in contact with saline solution (3.5% NaCl). Structural and morphological characterization by low-angle X-ray scattering, X-ray photoelectron spectroscopy, atomic force microscopy, thermogravimetric analysis, thickness, and adhesion measurements, showed for intermediate lithium content (500–2000 ppm) the formation of a highly polymerized PMMA phase covalently cross-linked by silica nodes, which provide strong adhesion to the aluminum substrate (15 MPa). Electrochemical impedance spectroscopy (EIS) results revealed an excellent barrier property in the GΩ cm2 range and durability of more than two years in a 3.5% NaCl solution. This performance can be attributed to the formation of a highly reticulated phase in the presence of Li, which hinders the permeation of water and ions. Additionally, the self-healing ability of scratched samples was evidenced by EIS assays showing a fast Li-induced formation of insoluble products in damaged areas; thus, constituting an excellent eco-friendly solution for corrosion protection of aerospace components. [ABSTRACT FROM AUTHOR]

• Development of covalently bonded PMMA-cerium oxide hybrid anticorrosive coatings. • Homogeneous distribution of cerium oxide nanoparticles in PMMA matrix. • Transparent and defect free coatings with excellent anticorrosive performance. • Extended coating lifetime by active corrosion protection. • Efficient, environmentally compliant and active protection of metallic surfaces. Metallic alloys are extensively used in many technological applications, however their susceptibility to corrosion causes huge economical losses and can result in failure of critical components. Aiming to obtain environmentally friendly, self-healing and high efficient anticorrosive coatings, organic-inorganic hybrids consisting of poly(methyl methacrylate) (PMMA) covalently bonded to CeO 2 /Ce 2 O 3 nanoparticles have been synthetized by the sol–gel process. Cerium oxide nanoparticles were covalently conjugated with the coupling agent 2-hydroxyethyl methacrylate (HEMA) and different proportions of methyl methacrylate (MMA), and subsequently the hybrid solutions were used to deposit films on A1020 carbon steel by dip-coating. The coatings are transparent, homogeneous, free of pores, have low surface roughness (<1.6 nm), and present good thermal stability (>220 °C). Excellent anticorrosive efficiency and durability was obtained by the nanoscale dispersion of cerium oxide nanoparticles into PMMA matrix, achieving for the sample with molar ratio of 1Ce:2HEMA:25MMA an impedance modulus up to 290 GΩ cm2, 8 orders of magnitude higher than the bare carbon steel, remaining essentially unchanged during 6 months exposure to saline solution. A detailed analysis of scratched coatings evidenced that Ce ions act as self-healing agents inhibiting the progression of the corrosion process. This work demonstrates that the active corrosion inhibition and environmental compliance make these PMMA-cerium oxide coatings a very promising alternative for the conventional protection systems. [ABSTRACT FROM AUTHOR]

Hypothesis The fraction of the silica/siloxane phase is a crucial parameter, which determines the structure and thus the properties of epoxy-siloxane-silica hybrid coatings. A careful adjustment of the colloidal precursor formulation allows tuning the nanostructure towards a highly condensed and cross-linked hybrid nanocomposite, suitable as an efficient anticorrosive coating. Experiments Novel epoxy-siloxane-silica hybrids have been prepared through the curing reaction of poly(bisphenol A-co-epichlorohydrin) (DGEBA) with diethyltriamine (DETA) and (3-glycidoxypropyl)methyltriethoxysilane (GPTMS), followed by hydrolytic condensation of tetraethoxysilane (TEOS) and GPTMS. At a constant proportion of the organic phase, the effects of the varying molar proportions of siloxane (GPTMS) and silica (TEOS) on the film properties have been investigated. Findings A detailed structural analysis suggests for intermediate TEOS to GPTMS ratios a structure of highly condensed silica-siloxane domains covalently bonded to the embedding epoxy phase. The homogeneous distribution of the quasi-spherical sub-nonmetric silica-siloxane nodes is in agreement with low surface roughness (<5 nm), observed by atomic force microscopy. This dense nanostructure results in high thermal stability (>300 °C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the GΩ cm 2 range. [ABSTRACT FROM AUTHOR]

Ti6Al4V is the mostly applied metallic alloy for orthopedic and dental implants, however, its lack of osseointegration and poor long-term corrosion resistance often leads to a secondary surgical intervention, recovery delay and toxicity to the surrounding tissue. As a potential solution of these issues poly(methyl methacrylate)-silicon dioxide (PMMA-silica) coatings have been applied on a Ti6Al4V alloy to act simultaneously as an anticorrosive barrier and bioactive film. The nanocomposite, composed of PMMA covalently bonded to the silica phase through 3-(trimethoxysilyl)propyl methacrylate (MPTS), has been synthesized combining the sol-gel process with radical polymerization of methyl methacrylate. The 5 μm thick coatings deposited on Ti6Al4V have a smooth surface, are homogeneous, transparent, free of pores and cracks, and show a strong adhesion to the metallic substrate (11.6 MPa). Electrochemical impedance spectroscopy results proved an excellent anticorrosive performance of the coating, with an impedance modulus of 26 GΩ cm2 and long-term durability in simulated body fluid (SBF) solution. Moreover, after 21 days of immersion in SBF, the PMMA-silica coating presented apatite crystal deposits, which suggests in vivo bone bioactivity. This was confirmed by biological characterization showing enhanced osteoblast proliferation, explained by the increased surface free energy and protein adsorption. The obtained results suggest that PMMA-silica hybrids can act in a dual role as efficient anticorrosive and bioactive coating for Ti6Al4V alloys. Unlabelled Image • Conjugation of silica and PMMA yielded homogeneous and adherent hybrid coatings. • PMMA-silica coatings provide efficient corrosion protection for a Ti6Al4V alloy. • Apatite formation in SBF solution predicts bone-bonding ability. • The coatings promote osteoblastic proliferation. • Effective protection metallic implants by bioactive anticorrosion coatings [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid coatings deposited on different types of metallic alloys have shown outstanding anticorrosive performance. The incorporation of osteoconductive additives such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) into organic-inorganic hybrid coatings is promising to improve the osseointegration and corrosion resistance of Ti6Al4V alloys, which are the most widely used metallic orthopedic and dental implant materials today. Therefore, this study evaluated the capability of poly(methyl methacrylate) (PMMA)-TiO 2 and PMMA-ZrO 2 hybrid coatings modified with HA and β-TCP to act as bioactive and corrosion protection coatings for Ti6Al4V alloys. In terms of cell growth and mineralization, osteoblast viability, Ca+2 deposition and alkaline phosphatase assays revealed a significant improvement for the HA and β-TCP modified coatings, compared to the bare alloy. This can be explained by an increase in nanoscale roughness and associated higher surface free energy, which lead to enhanced protein adsorption to promote osteoblast attachment and functions on the coatings. The effect of HA and β-TCP additives on the anticorrosive efficiency was studied by electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) solution. The coatings presented a low-frequency impedance modulus of up to 430 GΩ cm2, 5 decades higher than the bare Ti6Al4V alloy. These findings provide clear evidence of the beneficial role of HA and β-TCP modified hybrid coatings, improving both the biocompatibility and corrosion resistance of the Ti6Al4V alloy. Unlabelled Image • Modification of PMMA-TiO 2 and PMMA-ZrO 2 coatings with hydroxyapatite and β-TCP • The coatings provided effective corrosion protection for a Ti6Al4V alloy • Osteoblastic growth and mineralization were enhanced with calcium phosphate addition • Higher surface free energy and roughness promoted osteoblast proliferation • Achievement of a bioactive and anticorrosive coating for metallic implants [ABSTRACT FROM AUTHOR]