Mechanistic elucidation of the molecular weight dependence of corrosion inhibition afforded by polyetherimide coatings
Tiffany E. Sill, Victor Ponce, Carlos A. Larriuz, Ron Chertakovsky, Caroline G. Valdes, Torrick Fletcher, Jakob Nielsen, Kerry Fuller, Homero Castaneda, Rachel D. Davidson, Peter M. Johnson, Sarbajit Banerjee
Abstract
Corrosion of critical metal components exacts a heavy toll in terms of maintenance and replacement costs and damage to ecosystems upon failure. Polymeric barrier coatings protect against corrosion; however, design principles for modulating polymer structure to improve corrosion inhibition remain contested and elusive. Here, we examine molecular-weight-dependent differences in the efficacy of corrosion inhibition on aluminum substrates afforded by polyetherimide (PEI) coatings. Analyses of coated substrates evidence a clear trend denoting improved corrosion inhibition for higher weighted-average molecular weight ( M W ) PEI. The more rigid and entangled macromolecular network of higher- M W variants exhibit stable impedance values, |Z| 0.01 Hz ca. 10 10 Ω/cm 2 , upon extended immersion in brine media, whereas lower- M W variants are readily hydrated and disentangled resulting in a significant reduction in impedance values. Results illuminate mechanistic understanding of molecular-weight-dependence in corrosion inhibition, advance a framework for considering the dynamical evolution of secondary structure, and exemplify generalizable design principles for corrosion inhibition.