In solution, block copolymers — different types of synthetic polymer linked together — spontaneously cluster into a dazzling variety of shapes, including spheres, cylinders, discs and helices. Lately, even ring doughnuts (toroids) have been observed — but never alone, and always of varying size.
Taihyun Chang and his colleagues at Pohang University of Science and Technology in Korea have now hit on a recipe of copolymer and solvent that for the first time produces pure, almost uniform toroids — all about 70 nanometres in diameter and with a ring about 30 nanometres thick in cross-section. They are stable in solution for several months.
It is not clear how these doughnuts form; potential applications include use as templates for nanometre-scale patterning. For example, the researchers use them as a template to grow rings of gold nanoparticles around the doughnuts' edges.
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Polymer chemistry: Doughnut machine. Nature 459, 143 (2009). https://doi.org/10.1038/459143b
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DOI: https://doi.org/10.1038/459143b