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• 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]

• Novel covalently bonded PMMA-TiO 2 and PMMA-ZrO 2 hybrid nanocomposites. • Homogeneous distribution of fiber-like TiO 2 structures and ZrO 2 nanodomains. • Transparent and defect free coatings with excellent anticorrosive performance. • Elevated thermal stability and high coating adhesion to steel substrate. • Efficient environmentally compliant protection of metallic surfaces. The covalent conjugation between the phases of organic-inorganic nanocomposites and the careful tuning of the proportion of the colloidal precursors are essential to yield homogeneous, cross-linked and dense coatings that are able to protect metallic alloys against corrosion. In this work, the sol-gel route was used to prepare organic-inorganic hybrid coatings based on poly(methyl methacrylate) (PMMA) covalently bonded to TiO 2 or ZrO 2 nanoparticles through the coupling agent 2-hydroxyethyl methacrylate (HEMA), applied for the first time as anticorrosive coatings for metallic alloy. Different formulations of the hybrids were prepared by varying the proportion of titanium isopropoxide or zirconium propoxide, methyl methacrylate and benzoyl peroxide, and applied on carbon steel by dip-coating. The optimized parameters yielded for the two hybrids transparent and homogeneous coatings, with a thickness less than 3 μm, low surface roughness (<1.8 nm) and elevated thermal stability (>200 °C). Electrochemical impedance spectroscopy assays showed that PMMA-ZrO 2 and PMMA-TiO 2 coatings exhibit corrosion resistance up to 10 GΩ cm2, 7 orders of magnitude higher than the bare carbon steel, remaining essentially unchanged for PMMA-TiO 2 during 14 days exposure to 3.5 % saline solution. The results suggest that PMMA-ZrO 2 and PMMA-TiO 2 nanocomposites are suitable for application as environmentally compliant highly efficient anticorrosive coatings. [ABSTRACT FROM AUTHOR]

• High performance methyl methacrylate-silica anticorrosive coatings with long-term stability. • Correlation of structural characteristics with electrochemical barrier properties. • Modeling of the electrolyte permeation using the two-layer Young approach. • Comparison of electrical equivalent circuits using constant phase element and Young model. This work reports a detailed investigation of the structural and electrochemical barrier properties of PMMA-silica coatings. Hybrid nanocomposites were prepared by combining the sol-gel method with the polymerization of methyl methacrylate (MMA), using the thermal initiator benzoyl peroxide (BPO), followed by the hydrolytic condensation of tetraethoxysilane (TEOS) and 3-(trimethoxysilyl)propyl methacrylate. Raman spectroscopy and thermal analysis showed that the fine-tuning of the BPO amount, a critical synthesis parameter, improved the polymerization efficiency of MMA, leading to a highly cross-linked hybrid structure. The homogeneous coatings prepared under optimized synthesis conditions presented elevated thermal stability due to improved polymerization of the organic phase. Electrochemical impedance spectroscopy (EIS) showed a quasi-ideal capacitive impedance response in 3.5% NaCl solution, with low frequency impedance modulus of up to 10 GΩ cm2, which remained essentially unchanged during 19 months of immersion. This notable barrier property was modeled by fitting the EIS curves assuming slowly expanding electrolyte uptake, using the two-layer Young approach, and by comparison with the standard equivalent electrical circuit (EEC/CPE) model. The Young model provided valuable information on the time evolution of physical parameters including the thickness of the uptake zone, the conductivity depth-profile and the dielectric constant, among others, evidencing the high performance of the coatings. [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]