Surface-engineered nanocontainers for entrapment of corrosion inhibitors

The release properties and reloading ability of polyelectrolyte-modified halloysite nanotubes, polyelectrolyte-modified SiO2 nanoparticles, and polyelectrolyte capsules are studied. Three containers are distinguished by keeping the low-molecular-weight corrosion inhibitor benzotriazole in a hollow lumen inside or within the polyelectrolyte matrix and allowing release in either one direction or into all space dimensions. Polyelectrolyte shells, which modify the outer surface of the nanocontainers, are fabricated by using layer-by-layer assembly of poly (diallyldimethylammonium chloride)/poly(styrene sulfonate), poly(allylamine hydrochloride)/poly(styrene sulfonate), and poly(allylamine hydrochloride)/poly(methacrylic acid) polyelectrolyte bilayers. All nanocontainers reveal an increase of the benzotriazole release in aqueous solution at alkaline or acidic pH. The highest reloading efficiency (up to 80%) is observed for halloysite-based nanocontainers; however, after five reloading cycles the efficiency decreases to 20%. The application of appropriate nanocontainers depends on the demands required from feedback-active anticorrosion coatings. For coatings where the immediate release of the inhibitor is necessary, SiO2-based or halloysite-based nanocontainers with a shell consisting of weak polyelectrolytes are preferable. When continuous, gradual release is required, halloysite-based nanocontainers with a shell consisting of one weak and one or two strong polyelectrolytes are preferable.