Tuning Radial Lamellar Packing and Orientation into Diverse Ring-Banded Spherulites: Effects of Structural Feature and Crystallization Condition

Abstract

Spherulite morphologies of a highly asymmetrical double crystallizable poly(epsilon-caprolactone-b-ethylene oxide) diblock copolymer in solution-cast films were explored from a unified standpoint of tuning radial lamellar organization via controlled evaporation. Besides Maltese cross spherulites, three kinds of ring-banded spherulites that display non- and half-birefringent concentric ringed features as well as extinction banding were first encountered in the same polymer. Structural analyses based on atomic force microscopy, transmission electron microscopy, and grazing incidence X-ray technique revealed that concentric ringed spherulites possess the nature of a rhythmic variation of the radial lamellar packing and extinction banded spherulites have the origin of a periodic change of the radial lamellar orientation. Morphological transitions among different kinds of spherulites were achieved by altering the drying condition. PEO segment crystallized at low temperatures even if it is being confined by PCL lamellae. Combined with poly(e-caprolactone) and poly(ethylene adipate), the influences of structural feature and crystallization condition on radial lamellar organization of polymer spherulites were discussed. These present findings are encouraged to enhance our understanding and then governing generation of expected polymer crystal morphology for special material performance.