Epicycloid extinction-band assembly in Poly(decamethylene terephthalate) confined in thin films and crystallized at high temperatures

This work utilized an in-house synthesized aryl polyester, poly (decamethylene terephthalate) (PDT), to investigate the crystal assembly of unique camellia-flower-like extinction bands periodically assembled in spherulites formed at specific T_c's or driven by other kinetic factors. These extinction PDT bands at high T_c's (110–125 °C) and confined in thin films are packed by parallel flat plates of single-crystal-like dimensions in nanometer to micrometer scales (measuring 4 μm × 4 μm x 20 nm) self-assembled as terrace-like shingles that are bordered with an optically extinct boundary. The valley corresponds to where most amorphous ingredients accumulate and the growth precipitates suddenly from tip of ridge to near the substrate, resulting in an optical extinction border. All ridges (convex bands) are composed of discrete crystal plates aligned as roof-shingle stacks along the circumferential bands, and the crystals do not traverse across the bands. These lamellae on ridge bands are discrete and do not twist at all or rotate 360° angle continuously extending from nucleus to periphery. The circular-extinction bands of PDT of nanometer films (300–400 nm) are composed of parallel lamellae with the terrace alignment pointing along the circumferential direction; the epicycloid-extinction bands of thicker PDT specimens (2000–3000 nm) are assembled with single-crystal plates of lozenge shapes and aligned in growth-preferred directions to form petal-like tips.