As boring as . . .

Gregory Nemec

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When people ask Eric Dufresne '96 what he does for a living, he sometimes tells them that he watches paint dry.

But the associate professor of engineering is not making a crack about how boring his job is: he's speaking literally. As it turns out, watching paint dry can be quite interesting. When paint dries, it sometimes cracks. This problem is common to all coatings, in fact. (Consider the aging nonstick pan whose Teflon surface fails, ruining your scrambled eggs.) A coating is bound to the surface beneath by an adhesive force, but over time stresses on the coating overpower the adhesion—resulting in fractures.

Understanding what causes cracks could help engineers prevent them. But until now the process behind fracture has been elusive. Researchers had been able to quantify forces averaged out over the entire coating, but that generalized approach "gives a terrible picture of how fracture actually works," says Dufresne, who set out to get a clearer view.

To study forces at the site of the cracking, his team applied a layer of paint-like coating to a piece of rubber. This wasn't ordinary rubber, though: the researchers had embedded in it microscopic fluorescent beads. By tracking the way those beads were displaced while the coating dried and cracked, Dufresne and his colleagues were able to map the forces at work around the sites of fracture.

What they found was striking: "the mechanical stress at the tip of the crack is just much, much higher than everywhere else," says Dufresne. The research was published in the Proceedings of the National Academy of Sciences. "The hope is," says Dufresne, "we can use this to make more robust coatings." Further studies could examine different coatings under varied stresses, which might yield industrial applications, says Elizabeth Jerison '10, a coauthor on the study.

Will any scientists be eager to take the next shift of paint-watching duty? It may sound boring, says Jerison, enthusiastically, "but there are actually incredibly interesting unanswered questions."