Lamellar Assembly Mechanism on Dendritic Ring-Banded Spherulites of Poly(ε-caprolactone)

Grating Assembly Dissected in Periodic Bands of Poly (Butylene Adipate) Modulated with Poly (Ethylene Oxide)

Polarized optical microscopy (POM), scanning electron microscopy (SEM), and synchrotron microbeam wide-angle X-ray diffraction (WAXD) were used to investigate the mechanisms of periodic assemblies leading to ring-banded crystal aggregates with light-grating capacity for iridescence in poly (1,4-butylene adipate) (PBA) modulated with poly (ethylene oxide) (PEO). A critical finding is that the PBA crystal assembly on the top surface and in the interior constitutes a grating architecture, with a cross-bar pitch equaling the inter-band spacing. The inner lamellae are arranged perpendicularly to the substrate under the ridge region, where they scroll, bend, and twist 90° to branch out newly spawned lamellae to form the parallel lamellae under the valley region. The cross-hatch grating with a fixed inter-spacing in the PBA aggregated crystals is proved in this work to perfectly act as light-interference entities capable of performing iridescence functions, which can be compared to those widely seen in many of nature’s organic bio-species or inorganic minerals such as opals. This is a novel breakthrough finding for PBA or similar polymers, such as photonic crystals, especially when the crystalline morphology could be custom-made and modulated with a second constituent.

Unique Periodic Rings Composed of Fractal-Growth Dendritic Branching in Poly(p-dioxanone)

Amorphous poly(p-vinyl phenol) (PVPh) was added into semicrystalline poly(p-dioxanone) (PPDO) to induce a uniquely novel dendritic/ringed morphology. Polarized-light optical, atomic-force and scanning electron microscopy (POM, AFM, and SEM) techniques were used to observe the crystal arrangement of a uniquely peculiar cactus-like dendritic PPDO spherulite, with periodic ring bands not continuingly circular such as those conventional types reported in the literature, but discrete and detached to self-assemble on each of the branches of the lobs. Correlations and responsible mechanisms for the formation of this peculiar banded-dendritic structure were analyzed. The periodic bands on the top surface and interior of each of the cactus-like lobs were discussed. The banded pattern was composed of feather-like lamellae in random fractals alternately varying their orientations from the radial direction to the tangential one. The tail ends of lamellae at the growth front spawned nucleation cites for new branches; in cycles, the feather-like lamellae self-divided into multiple branches following the Fibonacci sequence to fill the ever-expanding space with the increase of the radius. The branching fractals in the sequence and the periodic ring-banded assembly on each of the segregated lobs of cactus-like dendrites were the key characteristics leading to the formation of this unique dendritic/ringed PPDO spherulite.

In-Situ Growth of Nucleus Geometry to Dual Types of Periodically Ringed Assemblies in Poly(nonamethylene terephthalate)

Monitoring of nucleus geometry and growth into dual types of periodically ring-banded morphology in poly(nonamethylene terephthalate) (PNT), respectively, Type-1 and Type-2, are done with detailed analyses using polarized-light optical microscopy (POM) in-situ CCD recording; the periodic assembly morphologies are characterized using atomic-force microscopy (AFM) and scanning electron microscopy (SEM). Different annealing treatments (Tmax = 110, 120, 130 °C) are accomplished at a crystallization temperature of 85 °C; effects on the nucleus geometry, number (25–10%) and volume fractions (33–15%) of Type-2 among two types of banded PNT spherulites are expounded. Growth of a specific type of periodically banded PNT spherulite is initiated from either highly elongated sheaf-like or well-rounded nuclei, with the final grown lamellae being self-packed as multi-shell structures. Nucleation geometry and crystallization parameters collectively lead to development of multiple types of banded PNT spherulites of different relative fractions.