Inhibition of Steel Corrosion and Alkaline Zinc Oxide Dissolution by Dicarboxylate Bola-Amphiphiles: Self-Assembly Supersedes Host-Guest Conception

Abstract

For many decorative applications like industrial and architectural paints, prevention of metal substrates from corrosion is a primary function of organic coatings. Triggered release of inhibitor species is generally accepted as a remedy for starting corrosion in case of coatings damage. A polyurethane based coating, doped with bola-amphiphiles of varying molecular weight but with a common head group motif that stems from ring-opened alkenyl succinic anhydride, enables passivation of the defect and mitigates cathodic delamination, if applied on cold rolled steel. An antagonistic effect results from the intercalation of the bola-amphiphiles into layered double hydroxide Zn2Al(OH)6 and subsequent incorporation of the hybrid phase into the organic matrix. In particular higher molecular weight bola-amphiphiles get immobilized through alkaline degradation of the layered framework in the basic milieu at the cathode. By means of sediments from colloidal states it is demonstrated that in-situ formed zinc oxide encapsulates the hybrid phase, evidenced by impeded dissolution of the ZnO based shell into caustic soda. While inhibition of steel corrosion results from a Donnan barrier layer, impeded zinc oxide dissolution is rooted in zinc catalyzed bola-amphiphile hydrolysis and layered deposition of the crystalline spacer diol hydrogenated bisphenol-A.

Tailoring Hybrid Layered Double Hydroxides for the Development of Innovative Applications

“…[147b,199] Corrosion inhibition in terms of performance is measured by direct current (DC) polarization experiments through the anodic and cathodic Tafel coefficients, enabling the determination of polarization resistance and inhibitor efficiency; the underlying corrosion process is measured by electrochemical impedance spectroscopy. The intricate and indirect role of bola‐amphiphile and acetate–ZnAl LDH embedded in a polyurethane‐based coating was recently reported in the context of steel corrosion inhibition . The passivation of the metal defect substrate is explained by the in situ hydrolysis of bola‐amphiphile and by the degradation of LDH into a ZnO phase near the cathodic sites, catalyzing the hydrolysis.…”

Epoxy coating with self‐healing capability based on a 2‐mercaptobenzothiazole‐loaded CeO2nanocontainer

“…To prevent agglomeration, the embedding of organic inhibitors in these materials has been reported to be an effective approach. The direct addition of organic inhibitors into coating formulations can lead to the fast exhaustion of the active anticorrosion potential and the osmotic blistering of the EP film under the uncontrollable release of organic inhibitors . The encapsulation of active materials and the preparation of nanocontainers have been introduced in the controllable release of organic inhibitors and the improvements of the lifetime and anticorrosive resistance of EP coatings .…”