Аннотация:We report on the banded polymer morphology of several semicrystalline
commodity polymers such as high-density poly(ethylene), poly(trimethylene terephthalate),
poly(vinylidene fluoride), and poly(3-hydroxybutyrate). The internal
structural organization and 3D shape of the constitutive crystalline lamellae have
been topics of interest in polymer physics for the last 50 years. However, conventional
morphological characterization techniques (electron and/or optical microscopy)
can be misleading in such analyses and have resulted in wrong interpretations
of the twisted lamella growth mechanisms. We present nanofocus synchrotron
X-ray scattering experiments and describe the analysis used to interpret the arrays
of nanodiffractograms acquired along the spherulitic radii. It is shown that the
crystal twist occurring during radial outward growth is regular and uniform. The 3D
lamella shape is in most cases similar to the classic helicoid, whereas in other cases,
such as the lamellae of poly(propylene adipate), it corresponds to a spiral structure.
Access to comprehensive microstructural information about bulk samples makes it
possible to better understand the twisted growth mechanisms and check the premises
of the Keith and Padden model linking the direction of chain tilt and lamella
twist hand. It is demonstrated that this model cannot explain the banding behavior in poly(trimethylene terephthalate) and therefore needs reconsideration. In-depth
analysis of the microstructure allows more general conclusions to be drawn regarding
correlation of chiralities pertinent to different spatial scales, ranging from that
of the constitutive monomer to the supramolecular level of twisted lamellae.