Real-time atomic force microscopy observation was carried out during crystallization in
thin films of chiral poly(R-3-hydroxybutyrate-co-R-3-hydroxyhexanoate) copolymer, and the development
details of single lamellae in the banded spherulites are revealed for the first time. The lamellae exhibit
complicated growth behaviors: twisting, bending, backward growth, and branching. The lamellae
continuously twist to show alternating edge-on and flat-on views along the radii of the spherulites. Giant
screw dislocations bring forth to the birth of new lamellae. Interaction between the leading and trailing
lamellae contributes to cooperative stacking of the twisting crystals. The lamellae twist before screw
dislocations appear, demonstrating that screw dislocations are not causal of twisting. All the observed
twisting occurs in the right-handed sense, likely resulting from the chirality of the crystal structure.
Increased crystallization temperature results in decreased magnitude of lamellar twisting and bending.
Models for morphological development are discussed in the context of these observations.
The phase morphology and surface composition of ethylene−vinyl acetate (EVAc) and
polypropylene (PP) blends were investigated in this work. It was found that the 70/30 PP/EVAc blend
formed a gradient phase morphology in the cross section by annealing. The particle size of the EVAc
dispersed phase increased gradually along the direction vertical to the sample surface from the middle
to the surface with increasing annealing time and temperature. The EVAc component on the surface of
the blends after annealing was detected using Fourier transform infrared spectroscopy coupled with
attenuated total reflectance (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). The
oxygen consistent with the EVAc on the surface of the PP/EVAc blends (70/30) also increases with
increasing time and temperature. It means that the component of the EVAc accumulates on the surface
with the formation of the gradient phase morphology in the blends. No significant difference in the gradient
phase morphology was found for both the thin and thick PP/EVAc blend samples at the same annealing
conditions. Moreover, the EVAc copolymer was melt-grafted with acrylamide (AAm) and then blended
with PP. It was also found that PP/EVAc-g-AAm formed a gradient phase structure during annealing,
the same as that of a PP/EVAc blend. With the dispersed phase EVAc as a carrier, the grafted polar
groups were transported onto the surface of the blend sample with formation of an EVAc gradient dispersed
phase. Thus, the gradient phase structure control of blends is an effective method for the material surface
modification of materials.
Banded spherulites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-3HV)) random copolymer
were prepared by isothermal crystallization at 90 °C for 10 h. Using tapping-mode atomic force microscopy
(AFM), the concentric periodic ridges and valleys on the surface of the banded spherulites of this polymer
were found to consist of edge-on and flat-on lamellae, respectively. The periodic concentric ridges and
valleys observed by AFM corresponded to the periodic extinction rings observed by polarized optical
microscopy. AFM measurements showed that the interaction between the AFM probe and the sample
surface can be significantly influenced by lamellar orientation.
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