Rhythmic Growth Combined with Lamellar Twisting Induces Poly(ethylene adipate) Nested Ring-Banded Structures

Previously, poly(epsilon-caprolactone) (PCL) classical ring banded spherulites with periodic twisted lamellae and nonclassical concentric ringed structures induced by rhythmic growth were obtained by modulating the competition between diffusion flux and spherulitic growth. In this study, the modulation of diffusion flux and spherulitic growth on ring-banded structures is further studied, and hierarchical nested ring-banded patterns with a banded structure nested in the ridge rings of the other concentric ringed structure are prepared during slow solvent evaporation in poly(ethylene adipate) (PEA) solution films. The structural characterizations reveal that the big concentric ringed structure derives from periodic variation of thicknesses and that the small inner banded structure consists of periodic twisted lamellae. A diffusion-induced rhythmic growth mechanism and an unbalanced surface stress induced lamellar twisting model are proposed to illustrate the formation of the big concentric and the inner banded structures, respectively.