Angew. Chem. Int. Edn doi:10.1002/anie.200900533 (2009)

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.