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Polymer Films Bend In The Spotlight

Light-driven reversible isomerization of soft materials causes them to flex and bend

by Elizabeth K. Wilson
November 8, 2010 | A version of this story appeared in Volume 88, Issue 45

Light causes reversible trans-cis flipping by the 3-D material’s azobenzene units.
Light causes reversible trans-cis flipping by the 3-D material’s azobenzene units.

A polymer film that bends in response to light may provide engineers with a new class of soft materials for artificial muscles and other three-dimensional devices (Science 2010, 330, 808). Takuzo Aida of the University of Tokyo and colleagues fabricated the material, from a bottle-brush-shaped polymer sandwiched between two sheets of undirectionally stretched polytetrafluoroethylene (PTFE). The polymer consists of dense paraffinic side chains containing three light-sensitive azobenzene units wrapped around polymethacrylate backbones. When the stretched PTFE sheets are hot-pressed, the polymer is forced into a freestanding film: The backbones stand up perpendicularly to the plane of the PTFE sheets, and the bottle-brush “bristles” align along the stretched PTFE plane. When exposed to ultraviolet and visible light, the azobenzene units undergo trans-to-cis and cis-to-trans isomerization, respectively—exposure to the light causes the entire film to flex and bend. “The width of the film, fabricated by this easy processing, is in principle unlimited,” the researchers write.


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