A Coating That Heals Itself

The life of underground pipelines, deep-sea oil well platforms, and sea-faring ships could be extended thanks to newly developed self-healing coatings that repair scratches, staving off corrosion. No external stimulus, such as UV light, is needed to initiate the healing process. This makes these coatings particularly attractive for preventing corrosion in hard-to-reach places, where replacing hardware or repairing surfaces is a major undertaking, said Paul V. Braun, a materials science professor at the University of Illinois, Urbana-Champaign, who led the research effort.

"Others have demonstrated self-healing coatings that repair superficial damage; however, ours is the first that can protect the substrate even when the damage goes all the way to the substrate," Braun said. The new coating's repair mechanism relies on tiny capsules—roughly 90 µm in diameter—that hold either a siloxane monomer or a catalyst made from tin or titanium salts. Damage to the coating causes these little balloons to burst, bleeding their contents into the damaged region, where they mix, polymerize, and repair the surface (Adv. Mater. 2009, 21, 645).

"You can take these capsules and add them to any coating," Braun noted. "The contents of the capsules are protected by the shell, so it's not critical that the coating be engineered to be nonreactive with the catalyst." He presented the research at the American Chemical Society's national meeting in Salt Lake City on March 25, during a session sponsored by the Division of Polymeric Materials: Science & Engineering.

Braun's new coatings "constitute a giant step toward winning the battle against corrosion," commented Christopher W. Bielawski, a chemistry professor at the University of Texas, Austin, who studies self-healing materials. "Surfaces coated with these materials not only show an outstanding resistance toward degradation under realistic conditions, but actually repair themselves upon being deliberately damaged. Another remarkable aspect of this work is the level of characterization and testing that was employed. It is clear that these self-healing coatings are the real deal," he told C&EN.