Atomic-Force and Optical Microscopy Investigations on Thin-Film Morphology of Spherulites in Melt-Crystallized Poly(ethylene adipate)

Abstract

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 (Tc = 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 edge-on 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 Tc = 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.