Hybrid Halloysite Nanotubes as Smart Carriers for Corrosion Protection

Novel hybrid halloysite nanotubes (HHNTs) were developed and used as smart carriers for corrosion protection of steel. For this purpose, as-received halloysite nanotubes (HNTs) were loaded with a corrosion inhibitor, imidazole (IM), by vacuum encapsulation. In the next step, a layer by layer technique was employed to intercalate another inhibitor, dodecylamine (DDA), in the polyelectrolyte multilayers of polyethylenimine and sulfonated polyether ether ketone, leading to the formation of HHNTs. During this process, IM (5 wt %) was successfully encapsulated into the lumen of HNTs, while DDA (0.4 wt %) was effectively intercalated into the polyelectrolyte layers. Later, the HHNTs (3 wt %) were thoroughly dispersed into the epoxy matrix to develop smart hybrid self-healing polymeric coatings designated as hybrid coatings. For a precise evaluation, epoxy coatings containing as-received HNTs (3 wt %) without any loading denoted to as reference coatings and modified coatings containing HNTs loaded with IM-loaded HNTs (3 wt %) were also developed. A comparative analysis elucidates that the hybrid coatings demonstrate decent thermal stability, improved mechanical properties, and promising anticorrosion properties compared to the reference and modified coatings. The calculated corrosion inhibition efficiencies of the modified and hybrid coatings are 92 and 99.8%, respectively, when compared to the reference coatings. Noticeably, the superior anticorrosion properties of hybrid coatings can be attributed to the synergetic effect of both the inhibitors loaded into HHNTs and their efficient release in response to the localized pH change of the corrosive medium. Moreover, IM shows an active release in both acidic and basic media, which makes it suitable for the protection of steel at the early stages of damage, while DDA being efficiently released in the acidic medium may contribute to impeding the corrosion activity at the later stages of deterioration. The tempting properties of hybrid coatings demonstrate the beneficial role of the development of novel HHNTs and their use as smart carriers in the polymeric matrix for corrosion protection of steel.