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Materials

A Quadruple Shape-Shifter

Nafion, the sulfonated fluoropolymer, can take on an unprecedented four different shapes as a shape-memory material

by Bethany Halford
March 15, 2010 | APPEARED IN VOLUME 88, ISSUE 11

Nafion, the sulfonated fluoropolymer, has a nifty, shape-shifting trick. Although it is best known for its use in proton-exchange membranes, Nafion is also a highly versatile shape-memory material, according to a discovery made by Tao Xie, a scientist at General Motors Research & Development Center, in Warren, Mich. (Nature 2010, 464, 267). Shape-memory materials can take on a temporary shape and then switch back to their original form when exposed to an external stimulus—in Nafion’s case, heat. A few instances of shape-memory polymers that switch between three different shapes have been reported, but Xie demonstrates that Nafion, also known as perfluorosulfonic acid ionomer, or PFSA, can move between four. No change in the material composition is required to elicit this quadruple shape-shifting behavior. Instead, Xie takes advantage of the material’s broad glass-transition temperature, from around 55 °C to 130 °C, fashioning each shape at well-separated intervals above the onset of the glass transition. “Other ionomers with broad glass transitions are likely to show similar shape-memory effects,” Xie notes.

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