Sophisticated dual-discontinuity periodic bands of poly(nonamethylene terephthalate)

Crystallized poly(nonamethylene terephthalate) (PNT) displays mirror-image and Fermat's-spiral ring-banded spherulites, respectively. The interior anatomy by SEM and AFM microscopic analyses shows that the lamellar arrangement of grating-board structures inside the 3D bulk banded PNT is correlated to top-surface topography of alternate ridge and valley bands. For the banded spherulites, tangential-oriented lamellae under the ridges and radial-oriented lamellae under the valleys are collectively arranged into mirror-image or spiral symmetry, where the tangential lamellae intersect at 90° angle with the branching radial lamellae. Moreover, the grating-layered structures of the tangential lamellae are viewed as the shish-crystals from which the kebab side-branches grow outwards in the radial direction. 3D models are proposed to illustrate the lamellar assemblies in both types of periodic bands. Morphological evolution and lamellar assembly with dual discontinuity are addressed to further establish 3-D models.