Structure and properties of epoxy-siloxane-silica nanocomposite coatings for corrosion protection

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)methyl triethoxysilane (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 degrees C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the G Omega cm(2) range. (C) 2017 Elsevier Inc. All rights reserved.