The Smart Paint Patrol

Materials science: Searching for coatings that change colors and touch themselves up.

The U.S. military has launched an offensive against one of its most stubborn enemies -- rust. The Army spends $10 billion a year dealing with it. Scraping and repainting is not only expensive, it requires the use of hazardous chlorinated solvents. So the Pentagon has funded a project, headed by the New Jersey Institute of Technology, that aims to create coatings that inhibit corrosion and virtually eliminate the need to repaint tanks. This "smart paint" would detect cracks when they occur in the coating and seal those cracks automatically -- and, on top of that, it would allow operators to change colors at the push of a button.

To understand what makes smart paint so smart, consider normal dumb paint, typically made up of two components: pigment particles, which provide color, and a polymer, which functions both as a dispersant (keeping the particles from clumping) and a glue. When water seeps underneath a coat of paint, the underlying metal corrodes. But smart paints prevent seepage and NJIT scientists are considering several strategies for creating them. One of the most promising would involve embedding minuscule carbon nanotubes in the polymer to make it electrically conductive. Also embedded in the polymer would be tiny paint-filled capsules, a micron or so wide. A crack in the paint surface would change
its electrical properties. Built-in sensors would pinpoint the problem and the capsules would open automatically, flowing into the crack and sealing the surface from further damage. To make color change possible, the scientists would add specially designed molecules that are sensitive to electrical signals. Send the right signal and these molecules would light up, overriding the background color -- say, brown -- with their own green or red hue.

All of this isn't as far-fetched as it may sound. Smart Coatings Program Leader Dan Watts of NJIT says most smart paint ingredients have already been developed. Making the nanotube-polymer hybrid is likely to be the biggest challenge, as both components are tough to manipulate. And nanotubes cost $1 million per pound. Nonetheless, the team hopes to have a prototype by 2005.