Ultrathin Transparent Nanobrick Wall Anticorrosion Coatings

It is important to find environmentally friendly replacements for chromate conversion coatings (CCCs) that are effective anticorrosion layers. In this work, high corrosion resistance is demonstrated with ultrathin (and transparent) multilayer coatings deposited on an aluminum alloy. Cationic polyurethane (PU) and anionic vermiculite clay (VMT) multilayer films were deposited from aqueous solutions using layer-by-layer assembly. The combination of relatively hydrophobic polyurethane and highly aligned clay platelets leads to excellent barrier properties for the PU/VMT coating in an aqueous environment. A 30 bilayer PU/VMT coating, with a thickness of only 300 nm, provides 2 orders of magnitude improvement in impedance and imparts corrosion protection for 5 days. Another advantage of this unique coating system is that no surface treatments are required prior to coating due to the strong adhesion of polyelectrolytes to the metal. The work demonstrates the use of novel LbL assembled nanocoatings as a potential replacement for chromate conversion pretreatments.