Lamellae Assembly in Dendritic Spherulites of Poly(l-lactic Acid) Crystallized with Poly(p-Vinyl Phenol)

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.

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

The self-assembly structures of lamellae in optical ring bands have a critical effect on their optical and physical arrangements. Two different types of dendritic banded spherulites (namely ring-banded and zigzag ring-banded) are formed in poly(ε-caprolactone)/poly (phenyl methacrylate) blend at crystallization temperatures of 42 and 46 °C, respectively. The difference in optical birefringence of ring bands in two types of spherulites is resolved by means of direct morphological comparison. Banded spherulites are fractured carefully to facilitate lamellar orientation analyses of both the top surface and the interior surface. The results have revealed the existence of tree-like dendritic fractal growth lamellar assemblies in both banded spherulites. The optical ring patterns of the banded spherulites are differentiated mainly by the fractal orientation of the edge-on crystal branches in the ridge region. On the basis of detailed morphological analysis, 3D-lamellar assembly mechanisms are proposed to explain the growth of dendritic ring-banded spherulites at 42 °C and dendritic zigzag ring-banded spherulites at 46 °C.

Periodic Fractal-Growth Branching to Nano-Structured Grating Aggregation in Phthalic Acid

Small-molecule phthalic acid (PA), confined in micrometer thin films, was crystallized in the presence of strongly interacting tannic acid (TA) to investigate crystal assembly and correlation between banded patterns and branching structures. Several compositions of the mixture of ethanol/water solutions and evaporation temperatures were also manipulated to investigate the kinetic effects on the morphology of PA crystals. With increasing evaporation rate, the morphology of PA crystals systematically changes from circular-banded spherulites to highly ordered grating-banded patterns. A unique periodic fractal-branch pattern with contrasted birefringent bands exists at intermediate evaporation rate, and this unique grating architecture has never been found in other banded crystals. Crystal assembly of these three periodic morphologies was analyzed by utilizing atomic-force microscopy (AFM) and scanning electron microscopy (SEM) to reveal the mechanisms of formation of hierarchical structures of PA. The detailed growth mechanisms of the novel fractal-branching assembly into circular- or grating-banded patterns are analyzed in this work.