Nano-Coatings Developed by Pitt Professor Keep Surface Cracks From Spreading

PITTSBURGH—Today at the American Chemical Society (ACS) Annual Meeting in San Diego, a University of Pittsburgh professor will present research on healing surface defects with nanocomposite coatings. Her research could help manufacturers prevent material failure caused by nanoscale cracks.

In the session "Polymer Nanocomposites," Anna C. Balazs, Robert Von der Luft Professor in the Pitt's Department of Chemical and Petroleum Engineering and a researcher in Pitt's Institute of NanoScience and Engineering, will discuss nanocomposite materials she has developed that can stop propagation of tiny cracks that start as nanoscale scratches. The application of such nanocomposite coatings could potentially yield defect-free surfaces that exhibit enhanced mechanical properties.

When products are manufactured in a mold, nanoscale nicks and scratches frequently result that have high concentrations of stress at their tips. "The material has been broken into, and it wants to relieve that stress, which leads to further propagation of the cracks and failure of the material," said Balazs.

To keep cracks from spreading, Balazs's idea was to add a polymer coat containing nanoparticles to the components after they came out of the mold. "We hypothesized, for entropic reasons, that the particles would migrate into the crack," she said. Her team generated simulations from equations, and their results were verified experimentally by Thomas Russell of the University of Massachusetts Amherst. In further tests, Balazs found that once the particles were in the crack, the particles relieved the stress of the crack and prevented it from propagating.

Balazs's method is convenient in that it doesn't rely on chemistry, but simply the physical law of entropy, for pushing particles into the cracks. "People have known about that in solvents, but what we found that is new is that the same is true in a polymer 'melt,'" she said.

Pitt's Institute of NanoScience and Engineering is an integrated, multidisciplinary organization that brings coherence to the University's research efforts and resources in the fields of nanoscale science and engineering.

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3/15/05/tmw