Materials that can change their shape on demand have many applications, and, thanks to a team in the United States, an extra means of production. Christian Santangelo, Ryan Hayward and their colleagues at the University of Massachusetts at Amherst report that they have devised a way to produce polymer sheets that can transform into pre-determined three-dimensional shapes and back again.
The researchers created gel sheets from polymers of N-isopropylacrylamide and benzophenone, a molecule that creates crosslinking between polymers when exposed to ultraviolet (UV) light. These sheets swell in water, but shrink when heated.
The team patterned the gel using a mask and an initial low dose of UV to define the polymer's overall shape, then used a higher dose through a different mask to create highly crosslinked regions in which swelling is reduced. By allowing more swelling in some areas than others, the authors created objects that can switch between sheets and spheres when heated and cooled (pictured), as well as others that can reversibly form caps, cones and more-complex surfaces.
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A new way to 3D shapes. Nature 483, 249 (2012). https://doi.org/10.1038/483249d
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DOI: https://doi.org/10.1038/483249d
