A novel six-petal spherulite morphology composed of a combination of a central hexagonal core hexagon-shaped ring bands and six fibrous stalks is discovered in a low-molecular-weight polyl-lactide acid LMw-PLLA that is melt crystallized at a specific Tc 110 C and confined in thin films. The structures are analyzed by using polarized optical microscopy POM and atomic force microscopy AFM. Discrete lamellae consisting of sequenced wide and small lamellae all in flat-on orientation with periodically up-and-down topology are packed in a ring-banded alignment while continuous lamellae in flat-on tilted or edge-on orientations are arranged in the fibrous region. On the six corners of a symmetric hexagon-banded spherulite the radial fibrous lamellae overlap with ring-band lamellae to show a mixed combination of ring-banded and fibrous patterns. The formation of coexisting ring-banded and fibrous patterns in a mixed morphology is associated with the lamellar packing and orientation. The radial fibrous lamellae at the six corners favorably occur in the growth fronts which are closer to the reservoir of materials of diffusing species. Superimposed on the radial lamellae hexagon-shaped ring bands repeat themselves on the outskirts of the central hexagon nuclei. The geometry of the initial crystal is believed to be the influencing factors in final spherulite patterns.
PLLA; ring bands; fibrous lamellae; assembly; hexagon crystal.
: 660.284 298 Hik c
Source article of jurnals macromolecular chemistry and physics