The thin-film morphologies of double-ring-banded and ringless spherulites in melt-crystallized poly(ethylene adipate) (PEA) were examined using atomic-force microscopy (AFM) and polarizing optical microscopy techniques with phase image and depth profiles. For the PEA ring-banded spherulites (T c ) 30 °C), edge-on lamellae, with top views shaped like a figure 8, are arranged in an orderly fashion on the ridges of ring bands, and the valley region of the ring bands is filled mainly with flat-on oval-shaped platelets. Between the edgeon and flat-on band regions, some ribbonlike long lamellae are present that propagate across these two regions. However, these three lamellar types are discrete, discontinuous, and independent, and they are not necessarily inter-related by physical turning. By contrast, in the ringless Maltese-cross spherulite (PEA crystallized at T c ) 35 °C), similarly figure-8-shaped edge-on lamellae and flat-on platelets are also present, but they are scattered randomly, and no long lamellae are present. Near or within the edge-on lamellae, cavities are present as a result of densification and/or reorientation. In contrast with some single-banded spherulites where the valleys usually have a featureless amorphous texture, the valleys in the double-ring-banded PEA spherulites are filled with plateletlike lamellae, whereas the ridges contain mainly figure-8-shaped lamellae.

In‐depth interpretation of ring‐banded spherulitic morphology, crystals, polymorphism, and complex melting behavior in poly(1,4‐butylene adipate) (PBA) were analyzed via a procedure of designing composite core‐shell spherulites, in which two lamellar patterns (ring‐band vs. ringless) were packed by subjecting to crystallization at two‐step temperature schemes with specific temperatures and times. By heating to 52 °C and holding at that temperature for 30 min annealing, the core can be stripped off by melting, and analysis specifically on the ring‐shell portion (with the ringless core stripped by controlled melting) proves that the highest melting peak (P4 at 55–57 °C) is likely associated with melting of the ring‐band lamellae. Furthermore, the unusually complex multiple melting in PBA can be attributed to all three widely proposed mechanisms: (1) multiple types of lamellae preexisting in crystallized PBA, (2) scan/heating induced remelting/reorganization, and (3) polymorphism of dual crystal cells. In addition, this study evidently shows that the extinction rings within the ring‐banded shell, regardless of alternate edge‐on and flat‐on mechanism or alternative origins, can be of all singly α‐crystal form, either initially or upon postheating temperature‐induced transformation. Thus, the type of crystal forms (α or β) in polymorphic PBA is mainly associated with temperature of crystallization (Tc = 28 or 35 °C), and not likely with lamellar orientation (flat‐on or edge‐on). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 892–899, 2008

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Nature tends to assemble hierarchical structures in similar ways to achieve compactness and functions. This work probes the interior lamellae assembly of crystalline spherulites of poly­(ethylene adipate) (PEA) with striking birefringence patterns versus some known biological structures for optical color diffraction. Three-dimensional dissecting onto interior lamellar structures of spherulites in poly­(ethylene adipate) (PEA) in bulk forms crystallized at 28 ± 3 °C were studied in correlation with thin-film forms. Interior morphology in bulk PEA samples revealed periodic hemisphere or arc-shaped layers resembling corrugate boards with liner-flute medium alteration. Interior spherulites clearly expose that the lamellae within the intralayer are kebabs (plates) in the radial direction while the interlayer region are thin sheaths (fibrils) composed of cilia-like lamellae in the tangential direction. The interior repetitive lamellar assembly of PEA banded spherulites in displaying periodic optical birefringence patterns is proven to highly resemble those in many biological structures for iridescence light interference.