CAMBRIDGE, Mass. January 8, 2008 From the structure of DNA to nautical rope to distant spiral galaxies, helical forms are as abundant as they are useful in nature and manufacturing alike. Researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have discovered a way to synthesize and control the formation of nanobristles, akin to tiny hairs, into helical clusters and have further demonstrated the fabrication of such highly ordered clusters, built from similar coiled building blocks, over multiple scales and areas.
The finding has potential use in energy and information storage, photonics, adhesion, capture and release systems, and as an enhancement for the mixing and transport of particles. Lead authors Joanna Aizenberg, Gordon McKay Professor of Materials Science at SEAS and the Susan S. and Kenneth L. Wallach Professor at the Radcliffe Institute for Advanced Study, and L Mahadevan, Lola England de Valpine Professor of Applied Mathematics at SEAS, reported the research in the January 9 issue of Science.
"We demonstrated a fascinating phenomenon: How a nanobristle immersed in an evaporating liquid self-assembles into an ordered array of helical bundles. This is akin to the way wet, curly hair clumps together and coils to form dreadlocksbut on a scale 1000 times smaller," said Aizenberg.
To achieve the "clumping" effect, the scientists used an evaporating liquid on a series of upright individual pillars arrayed like stiff threads on a needlepoint canvas. The resulting capillary forcesthe wicking action or the ability of one substance to draw another substance into itcaused the individual strands to deform and to adhere to one another like braided hair, forming nanobristles.
"Our development of a simple theory allowed us to further characterize the combination of geometry and material properties that favor the adhesive, coiled self-organization of bundles and enabled us to quantify the conditions f
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