Monodispersed Nanodiamonds for Enhanced Anticorrosion of Waterborne Epoxy Coatings

Nanodiamonds (NDs) prepared by the explosion method possess very large surface energies, resulting in serious agglomerates, limiting their further application. Herein, we employed the strong shearing action of hydroxyl ion (OH-) to induce the hydrolysis of esters between the ND primary particles, generating the carboxyl and hydroxyl groups, breaking hard agglomeration of NDs, and successfully constructed electrical double layers on the surface of NDs via deprotonation of surface oxygen-containing groups induced by the strong shearing action of hydroxyl ion (OH-), leading to a significant increase of zeta potential absolute value (-54.2 mV), achieving the long-term stable (200 days) monodispersion of NDs (m-NDs). The as-obtained m-NDs, as efficient nanofillers, were added into the waterborne epoxy (WEP) to produce a composite coating of m-NDs/WEP, displaying a considerable improvement in anticorrosion performance. The results of electrochemical impedance spectroscopy show that the |Z| (f = 0.01 Hz) of m-NDs/WEP is nearly 3 orders of magnitude higher than that of pure WEP after 168 h of immersion. The excellent anticorrosion performance of m-NDs/WEP can be ascribed to the excellent compatibility, electrical insulation property, and physical barrier behavior of m-NDs, inhibiting the infiltration of corrosive medium. The molecular dynamics simulation reveals that m-NDs have good barrier properties against a corrosive medium.