Materials Science

Aperiodic Polymer Tiles

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Science  01 Jun 2007:
Vol. 316, Issue 5829, pp. 1255
DOI: 10.1126/science.316.5829.1255b

Quasicrystals have sufficient long-range order to produce a diffraction pattern, but do not show the three-dimensional translational periodicity found in normal crystals. They have been observed in metallic and small molecular systems, often through small compositional changes in the materials, although in many cases the quasicrystals are of poor quality and stability. Hayashida et al. show this sort of patterning over a much larger length scale in three-arm block copolymers made of polyisoprene (I), polystyrene (S), and poly(2-vinylpyridine) (P) mixed with a polystyrene homopolymer. Previously this system has been shown to form the (3.3.4.3.4) Archimedean tiling structure, with every vertex surrounded by a pattern of triangle (3) and square (4) cells. Upon changing the I:S:P ratio, the ratio of triangles to squares shifted from the Archimedian value of 2 to 2.305, and a dodecagonal quasicrystal pattern emerged. The tiling, however, was not perfect: Transition regions led to sections showing sixfold symmetry and a triangle-to-square ratio of 8:3. When the composition of the blend was changed further, the overall quasiperiodicity of the triangles and squares was lost. Thus, it may be possible to tune the tiling patterns through small changes in the polymer composition. MSL

Phys. Rev. Lett. 98, 195502 (2007).

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