Unusually negative, single ring-banded spherulites of poly(ethylene adipate) formed via controlled stepwise evaporative crystallization

Abstract

Double ring-banded poly(ethylene adipate) (PEA) spherulites consisting of periodically twisted lamellae were usually observed. In this work, besides the usually positive and negative spherulites, we report a novel transitional morphology of negatively birefringent, single ring-banded PEA spherulites formed in solution-cast films via controlled stepwise evaporative crystallization. The periodic structure shows a nature of rhythmic change of thickness deriving from alternating stacks of lamellar crystals with tilted or even edge-on orientations, and its negative birefringence is attributed to the coupling of spherulite radius of the a*-axis and the strongly oblique orientation of the lamellae in ridges. We believe that such evaporative-flow-induced rhythmic crystal growth into ringed structures can be observed for most crystallizable polymers under suitable crystallization conditions.