Shapeshifting Material Unfolds with Time


A new hydrogel material can change shape on its own schedule.

The hydrogel — vividly demonstrated in a blushing pink flower that opens its petals gradually over two hours — is the first shapeshifting material that changes in response to an internal clock, rather than an external trigger. In this case, that clock is the lifetime and concentration of temporary hydrogen bonds within the gel.

The hope, says Sergei Sheiko, a professor of chemistry at the Univ. of North Carolina at Chapel Hill, is to use the concept in applications where one would like to change the properties of a material but setting an external trigger like light or thermal change is tough: for example, four miles deep in an oil-well borehole or inside the human body, where temperature and darkness are constant.

“In many practical situations, it is sometimes impossible to apply any trigger,” Sheiko says.

Sheiko and his colleagues created the hydrogel by copolymerizing N,N-dimethylacrylamide (DMAA) and methacrylic acid (MAAc). The resulting copolymer is linked by two types of bonds. The first, present in low concentrations, are permanent covalent bonds. In addition to these permanent crosslinks, the hydrogel contains a higher concentration of temporary links — hydrogen bonds that act as the...

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