Structured growth from sheaf-like nuclei to highly asymmetric morphology in poly(nonamethylene terephthalate)

Thorough microscopy analyses are done on dissecting 3D interiors of poly(nonamethylene terephthalate) (PNT) banded spherulites. Growth of a specific type (Type-I) of banded spherulites is initiated from highly elongated sheaf-like nuclei, with asymmetrically grown lamellae packed as a multi-shell structure, leading to resemblance of a dual-face spheroid. Top-surface bands are characterized with discrete/ unconnected dots of crystals aligned as zig-zag circles, which correspond to interior layered lamellae ends surfacing to top. Thus, the banded spherulites display not only inter-band discontinuity, but also discontinuity among the dotted crystals aligned on the top-surface ridges. 3D analysis exhibits that the banded spherulites possess a Janus-face morphology of compounded shell-and-kink lamellae assembly with dual discontinuities.