Fig. 4: A mechanistic view of the effect of molecular weight on the efficacy of corrosion inhibition of PEI coatings. | npj Materials Degradation

Fig. 4: A mechanistic view of the effect of molecular weight on the efficacy of corrosion inhibition of PEI coatings.

From: Mechanistic elucidation of the molecular weight dependence of corrosion inhibition afforded by polyetherimide coatings

Fig. 4

The figure sketches the molecular-weight-dependent evolution of polymer packing and entanglements, which in turn governs diffusion-related permeation and selective ion retention. a Schematic illustration of the free volume and chain-packing density of short-chain, lower-molecular-weight variants of PEI; b schematic illustration of hydration of the polymer backbone and stabilization of water clusters, resulting in chain separation, and creation of void space. The resulting channels permit transport of corrodent species to the coating/metal interface wherein they can initiate corrosion processes and solubilize the corrosion product based on ligand-exchange; c schematic illustration of increased entanglement and chain-packing density of longer-chain higher-molecular-weight PEI coating variants. d Permeation of water but sequestration of ions mediated by the more rigid glass matrix formed by higher-molecular-weight variants of PEI coatings on AA 7075 substrates, which thereby preserve interfacial adhesion and show greater efficacy of corrosion inhibition.

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