Polymorphism and grating assembly with unique iridescence features in periodically banded poly(ethylene adipate)

Poly(ethylene adipate) (PEA) forms either ring-banded spherulites (RBS) crystallized between T_c = 20–32 °C, or ringless spherulites (RLS) if crystallized away from this range. Morphologies differ correspondingly in their interior structures, as well as polymorphism in that α-form crystal is packed in RLS but combination of α, β crystals are dominantly in ring-banded one. Internal structure of banded spherulites is determined by dissection analyses. Interior lamellae of the banded PEA spherulites are assembled as discontinuous concentric-shell structures with concave shapes like cut onions. The radial-direction plate-like lamellae intersection constitutes each shell with the tangential cilia-like lamellae. Interior tangential lamellae bend or branch out perpendicularly at 90° angle in the radial direction to merge with the radial plate-like lamellae. Through designing optimal regularly-banded morphologies, prominent photonic iridescence is attained in the PEA banded spherulites. Moreover, the PEA banded spherulitic morphology can structured the light with circular pattern by laser interference. Light-interfering grating structures for iridescence applications can be achieved by custom-designing the PEA-RBS assemblies.