Release kinetics study and anti-corrosion behaviour of a pH-responsive ionic liquid-loaded halloysite nanotube-doped epoxy coating

This study focuses on the release kinetics of inhibitor-loaded nanocontainers and the anti-corrosive properties of epoxy coatings doped and undoped with the nanocontainers. In this work, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] was loaded into halloysite nanotubes (HNTs), and the loaded HNTs were encapsulated with polyethyleneimine (PEI)/polyacrylic acid (PAA) and poly(diallyldimethylammonium chloride) (PDADMAC)/polyacrylic acid (PAA) to allow controlled release upon pH stimuli. The polyelectrolyte layer deposition was characterized using zeta potential analysis, and the release profiles were evaluated in neutral, acidic, and alkaline media. The release kinetics was studied and found to conform to the Ritger-Peppas and Korsmeyer-Peppas model, and the results proved that the combination of weak polyelectrolytes (PEI and PAA) provided a good response for up to 50% release of [Bmim][Cl] in acidic and alkaline media after 72 hours. The loaded HNTs encapsulated with the PEI/PAA combination were incorporated into an epoxy coating matrix and applied on an X52 steel substrate. The corrosion resistance of the coated and uncoated substrates was evaluated using electrochemical impedance spectroscopy (EIS) after immersion in a 3.5 wt% NaCl solution up to 72 hours. An artificial defect was created on the coating prior to immersion to evaluate the active corrosion inhibition ability. The coating doped with the smart pH-responsive halloysite nanotubes showed promising results in corrosion protectiveness even after 72 hours of exposure to a salt solution through EIS and SEM. Enhanced corrosion resistance was obtained for steel coated with epoxy resin doped with pH-responsive halloysite nanotubes loaded with ionic liquid.