From Nano-Crystals to Periodically Aggregated Assembly in Arylate Polyesters-Continuous Helicoid or Discrete Cross-Hatch Grating?

This work used several model arylate polymers with the number of methylene segment n = 3, 9, 10, and 12, which all crystallized to display similar types of periodically banded spherulites at various T-c and kinetic factors. Universal mechanisms of nano- to microscale crystal-by-crystal self-assembly to final periodic aggregates showing alternate birefringence rings were probed via 3D dissection. The fractured interiors of the birefringent-banded poly(decamethylene terephthalate) (PDT) spherulites at T-c = 90 degrees C revealed multi-shell spheroid bands composed of perpendicularly intersecting lamellae bundles, where each shell (measuring 4 mu m) was composed of the interior tangential and radial lamellae, as revealed in the SEM results, and its shell thickness was equal to the optical inter-band spacing (4 mu m). The radial-oriented lamellae were at a roughly 90 degrees angle perpendicularly intersecting with the tangential ones; therefore, the top-surface valley band region appeared to be a submerged U-shape, where the interior radial lamellae were located directly underneath. Furthermore, the universal self-assembly was proved by collective analyses on the three arylate polymers.

Automated summary

This study used different model arylate polymers to investigate their crystallization behavior, and found that they all formed periodically banded spherulites with similar characteristics. By dissecting these structures in 3D, the universal mechanisms of crystal-by-crystal self-assembly from the nano- to microscale were revealed, resulting in the formation of final periodic aggregates. Fracture analysis showed that the birefringent-banded poly(decamethylene terephthalate) (PDT) spherulites contained multi-shell spheroid bands composed of perpendicularly intersecting lamellae bundles.