Barrier properties of high performance PMMA-silica anticorrosion coatings

[Display omitted] •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.