CALL it the yoga polymer: Nafion, a material used in some fuel cells, has an unrivalled memory for contortions.
Tao Xie at General Motors in Warren, Michigan, has twisted and stretched a Nafion strip into three distinct shapes, and found that it will revert to each shape at the appropriate temperature.
Nafion becomes softer as it is heated. At 140 °C Xie stretched it into a particular shape, which was locked in the polymer’s “memory” as it cooled to 107 °C and stiffened. Stretching and cooling it twice more allowed two other shapes to be memorised, so that when heated…
