image: Researchers have determined how to control the shape of a polymer system at the micro-scale with a technique akin to half-tone printing. The polymer they use swells like a microscopic sponge when exposed to water, however printing "resist dots" in the polymer substrate creates points that will not swell (1). When all resist dots in one area are the same size, the area undergoes uniform expansion and the structure remains flat (2). When the dot size changes, however, buckling occurs from the mismatch in growth from one area to another (3). With a proper half-tone pattern of resist dots, almost any 3-D shape can be achieved. The illustration shows a square piece of polymer. Each side of the square is roughly the width of a mechanical pencil lead. If it were possible to draw a world map on this square, we could watch the map warp and wrap itself into almost a perfect sphere, a micro-globe. view more
Credit: Zina Deretsky, National Science Foundation
Christian Santangelo, Ryan Hayward and colleagues at the University of Massachusetts Amherst recently employed photographic techniques and polymer science to develop a new technique for printing two-dimensional sheets of polymers that can fold into three-dimensional shapes when water is added. The technique may lead to wide ranging practical applications from medicine to robotics
The journal Science publishes the research in its March 9 issue.
Researchers used a photomask and ultraviolet (UV) light to "print" a pattern onto a sheet of polymers, a technique called photolithography. In the absence of UV exposure, the polymer will swell and expand uniformly when exposed to water, however when polymer molecules within the sheet were exposed to UV light they became crosslinked--more rigidly linked together at a number of points--which prevented them from expanding when water was added. Patterning the amount of crosslinking across an entire sheet allowed researchers to control how much each area swelled. A second exposure to a carefully selected pattern of UV light allowed them to create specific 3-D shapes.
The work, supported by National Science Foundation (NSF) Faculty Early Career Development and Materials Research Science and Engineering Centers awards, is a collaborative effort between polymer engineering and physics, with both theoretical and experimental aspects.
"This paper reports an interesting fusion of experimental technique and theory to develop an innovative method for making self-actuating materials that will assume a desired three-dimensional shape," said Daryl Hess, a program director in the division of materials research at NSF.
For more information on this discovery, read the news release from the University of Massachusetts Amherst.
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Science