Concentric ring-banded spherulites of six-arm star-shaped poly(ε-caprolactone) via subcritical CO2

Abstract

Birefringent Maltese-cross concentric ring-banded spherulites with radial periodic variation of thicknesses grown from six-arm star-shaped poly(ε-caprolactone) (PCL) under the condition of subcritical CO₂ were observed in this study. The structure of unique unclassical ring-banded spherulites was found to be different from that of traditional ring-banded spherulites which formed by periodic twisting of lamellar crystals along the spherulite radial direction. Laser scanning confocal microscopy, atomic force microscopy and scanning electronic microscopy images revealed that the ring-banded structure consisted of alternating periodically ridge and valley bands with continuous edge-on lamellae. A two-steps growth mechanism of ring-banded spherulites has been proposed to explain the development of central crystals and periodic ring-bands via CO₂.