CHEMISTRY: A Reservoir to Reduce Rust

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Science  21 Jul 2006:
Vol. 313, Issue 5785, pp. 274c
DOI: 10.1126/science.313.5785.274c

Many coatings that effectively impede the corrosion of metal surfaces contain chromates, which pose a substantial toxicity hazard. Conversely, passive polymer coatings can be damaged, and thus allow corrosive species to penetrate through to the metal surface. A polymer coating can be augmented using sol-gel techniques to add a thin organic or hybrid film that acts as a second barrier and also improves adhesion. Such layers are even more effective when doped with active corrosion inhibitors, but, over time, the inhibitors can weaken the structural integrity of the film. An appealing solution would be to use nanometer-scale reservoirs that bind corrosion inhibitors and release them in active form upon changes in pH, light, or humidity.

Shchukin et al. used layer-by-layer deposition to prepare reservoirs with pH-responsive storage and release characteristics for aluminum surface protection. They coated silica nanoparticles with alternating poly(ethylene imine) and poly(styrene sulfonate) layers that entrapped a benzotriazole inhibitor and rendered it compatible with a zirconia/silica-based sol-gel coating. Electrochemical impedance measurements revealed that the corrosion resistance of films loaded with these reservoirs was comparable to that of the undoped sol-gel film and superior to that of sol-gel films treated with free benzotriazole. When the coatings were damaged with a microneedle before the measurements, the reservoir-doped films evinced a self-healing capacity and much longer-lasting corrosion resistance. — MSL

Adv. Mater. 18, 1672 (2006).

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