Figure 4. Fiber energy and structure.

(a) Hexagon, pentagon and octagon bulk structures used to compute the bulk energy e_b—and thus the rescaled tension σ̃—with unit cells outlined in orange (see Methods). Their structures are inspired by aggregates grown under high tensions. The two octagon bulks have identical energies per particle; note that while their polygons superficially appear to have only six sides on the figure, they are actually octagons with two pairs of perfectly aligned sides appearing as longer sides. (b) The energy per particle of infinite fibers based on those shown in Fig. 3 is higher that of the bulk, implying that they are nonequilibrium structures. (c) Defects, i.e., four-coordinated and two-coordinated vertices, are apparent upon closer inspection of some fibers from Fig. 3 (arrows).