Rubber bands may provide important clues for fabricating a variety of 3D shapes from flat parts, according to results published April 23, 2014, in the open access journal PLOS ONE by Jia Lui from Harvard and colleagues.
While setting out to fabricate new springs to support a cephalopod-inspired imaging project, the scientists stumbled upon the hemihelix, a shape rarely seen in nature. Helices are 3D spiral structures, much like a corkscrew or a slinky toy. Hemihelices form when the direction or handedness in which the spiral turns—known as the chirality—changes or reverses periodically along the helix's length. To better understand whether the observed 3D structures were randomly occurring, or whether specific factors controlled their formation, scientists stretched, joined, and then released rubber strips, and then numerically simulated and analyzed the shape-forming process.
By testing differences in the aspect ratio, or the width-to-height ratio of the rubber strips, the authors discovered that when a strip is wide relative to its height, it produces a helix. Further measurements revealed that there may be a critical value of the aspect ratio at which the shape transitions from a helix to a hemihelix, with periodic reversals of chirality. The authors suggest that this phenomenon has not yet been observed because other classes of materials simply break when stretched to the mismatched strains used in these tests.
Knowing precisely how to make the structures predictably and consistently may enable scientists to mimic these geometrical features in new molecules that may eventually lead to advances in modern nanodevices, including sensors, resonators, and electromagnetic wave absorbers.
"Once you are able to fabricate these complex shapes and control them, the next step will be to see if they have unusual properties; for example, to look at their effect on the propagation of light," says co-author Dr. Katia Bertoldi, Associate Professor at Harvard.
Adapted by PLOS ONE from release provided by Paul Karoff, (617) 496-0450
Citation: Liu J, Huang J, Su T, Bertoldi K, Clarke DR (2014) Structural Transition from Helices to Hemihelices. PLoS ONE 9(4): e93183. doi:10.1371/ journal.pone.0093183
Financial Disclosure: This work was supported by the Materials Research Science and Engineering Center under NSF Award No. DMR-0820484. K.B. also acknowledges support from the National Science Foundation (CMMI-1149456-CAREER) and the Wyss institute through the Seed Grant Program. D.R. acknowledges funding from the National Science Foundation (CMMI-1333835). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interest Statement: The authors have declared that no competing interests exist.
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