How to build doughnuts with Lego blocks (Vol. 43 No. 1)

image A mix of two chemically discordant polymers with strong bonds creates previously unseen nanoscale assemblies

The present work reveals how nature minimises energy costs in rings of liquids with an internal nanostructure made of two chemically discordant polymers joined with strong bonds, or di-blocks, deposited on a silicon surface.

The authors first created rings of di-block polymers that they liken to building doughnuts from Lego blocks due to the nature of the material used, which has an internal structure discretised like Lego blocks, resulting in rings approximating the seamless shape of a doughnut (see photo).

The dynamics of interacting edges in ring structures that display asymmetric steps, i.e., different spacing inside and outside the ring, when initially created, has been measured. It is found that the interaction shaping the ring over time is the repulsion between edges. The source of this repulsion is intuitive: an edge is a defect which perturbs the surface profile with an associated cost to the surface energy.

These edges could be considered as defects in a material with an otherwise perfect order at the nanoscale. Thus, research based on the elucidation of defect interactions could help scientists trying to eliminate such defects by understanding how these materials self-assemble. Such systems could also provide an ideal basis for creating patterns on the nanoscale, data storage, and nanoelectronics.

Dynamics of interacting edge defects in copolymer lamellae
J. D. McGraw, I. D. W. Rowe, M. W. Matsen and K. Dalnoki-Veress, Eur. Phys. J. E, 34, 131 (2011)
[Abstract]