Zur Struktur des PolyÄthylens

Depletion-Induced Nonbirefringent Banding in Thin Isotactic Polystyrene Thin Films

“…These typical bands appear in sharp contrast under all specimen orientations of plane-polarized light but exhibit very poor contrast under unpolarized light. In contrast, in the 1950s, Schuur, 3 Schramm, 4 and Keith 5 reported observations of banded spherulites in which the bands appeared in sharp contrast in unpolarized light as well as under polarized light. Further, under plane-polarized light, the bands disappear when the plane of polarization is perpendicular to the bands.…”

Phase Behavior and Rhythmically Grown Ring-Banded Spherulites in Blends of Liquid Crystalline Poly(aryl ether ketone) and Poly(aryl ether ether ketone)

“…[26][27][28][29][30] It is generally believed that the extinction bands in spherulites are due to periodic twisting of lamellae along the radial growth direction of the spherulites. [31][32][33][34][35][36][37][38][39][40] However, in the 1950s, on the basis of the fact that the same concentric rings in polyethylene spherulites were observed under an unpolarized configuration, [41][42][43] Keith and Padden proposed that the lamellar twisting cannot be the only cause for the observed concentric ringed patterns in polymer spherulites, and the concentric ringed pattern is a consequence of structural discontinuities caused by rhythmic crystal growth as well. 44,45 Recently, rhythmic crystal growth of ring-banded spherulites in some blends of crystalline and amorphous polymers has been observed experimentally 46,47 and explained by simulation.…”

“…Ring-banded spherulites are often observed under polarized optical microscope in some semicrystalline homopolymers − and polymer blends. − It is generally believed that the extinction bands in spherulites are due to periodic twisting of lamellae along the radial growth direction of the spherulites. − However, in the 1950s, on the basis of the fact that the same concentric rings in polyethylene spherulites were observed under an unpolarized configuration, − Keith and Padden proposed that the lamellar twisting cannot be the only cause for the observed concentric ringed patterns in polymer spherulites, and the concentric ringed pattern is a consequence of structural discontinuities caused by rhythmic crystal growth as well. , Recently, rhythmic crystal growth of ring-banded spherulites in some blends of crystalline and amorphous polymers has been observed experimentally , and explained by simulation . Very recently, Schultz et al reported a depletion-induced nonbirefringent banding in isotactic polystyrene thin films, which is similar to the rhythmic crystallization processes …”

Crystallization in Polymer Thin Films: Morphology and Growth

“…In one case, Duan et al 47 and Wang et al 48 found concentric-ringed structures, similar to banded spherulites in the bulk and thin films. [48][49][50][51][52] The second case was originally discovered by Keith and coworkers 13 and later revisited by Zhang et al 39 This is the curved or scrolled crystals of PE. These dendritic crystals are curved along the long axis of the branches.…”