Branching and Higher Order Structure in Banded Polyethylene Spherulites

Toda, Akihiko; Okamura, Mari; Taguchi, Ken; Hikosaka, Masamichi; Kajioka, Hiroshi

doi:10.1021/ma702267e

Cited by 81 publications

(114 citation statements)

References 72 publications

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“…In our previous papers, we have reported successful confirmation of the predicted square root dependence of m on VD À1 (or V) in terms of the temperature dependence for polyethylene 16 and polybutene-1, 17 irrespective of the higher order structures of banded and non-banded spherulites. For the banded spherulites of polyethylene, the proportional relationship between P and m in eq 1 has also been confirmed.…”

Section: 2mentioning

confidence: 54%

“…[18][19][20] We have recently suggested a splaying instability due to a gradient field of free energy at the growth front and experimentally confirmed the predicted dependence for the case of banded polyethylene spherulites and non-banded polybutene-1 spherulites. 16,17 As the splaying instability of growth front, we have suggested two possibilities of the gradient in free energy at the growth front formed by (1) compositional gradient of non-crystallizing fractions (MullinsSekerka's type 21,22 ) and by (2) pressure gradient due to the difference in densities of the crystal and the melt (SaffmanTaylor's type 23,24 ). The gradient in free energy accelerates the fluctuation of the growth front and the surface tension suppresses the fluctuation; the balance of those two effects determines the critical lateral width, m .…”

Section: 2mentioning

confidence: 99%

“…We have examined the banded spherulites of polyethylene and non-banded spherulites of polybutene-1 in our recent studies. 16,17 The present paper is therefore for the further confirmation of the following proposed mechanism on the banded spherulites of poly(vinylidene fluoride), PVDF.In our proposed modeling of the branching and reorientation of lamellar crystals, we have suggested the possibility of a splaying instability of the growth front as the source of branching; the lateral width of each lamellar crystal is limited at a critical width, i.e., maximum lateral width, above which the crystal splays into branches. After the branching, the branches will be spontaneously re-oriented due to torsional inherent stress in the case of banded spherulites.…”

mentioning

confidence: 99%

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Branching and Higher Order Structure in Banded Poly(vinylidene fluoride) Spherulites

Toda

Taguchi

Hikosaka

et al. 2008

Polym J

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The formation mechanism of banded spherulites of poly(vinylidene fluoride) has been examined experimentally by optical and atomic force microscopies. We have confirmed the proportional relationship between the band spacing and the maximum lateral width of lamellar crystals at the growth front, and the square root dependence of the maximum width and the band spacing on the growth rate. The square root dependence suggests a splaying instability of the growth front regulated by a gradient of free energy in the liquid side, and the proportional dependence suggests the dominant effect of torsional reorientation on the occasion of splaying in the period determination of band spacing.KEY WORDS: Spherulites / Poly(vinylidene fluoride) / Branching / Crystallization of polymers from the melt evolves as a higher-order structure of spherulite with radiating and space filling branches. A number of polymer spherulites accompany concentric ring pattern in them and are called banded (or ringed) spherulite. The formation mechanism of spherulites in general and that of banded spherulites specifically have been studied for many years, but the fundamental mechanism of the pattern formation has not been clarified yet. 1,2The concentric ring pattern in polymer spherulites is caused by an optical birefringence of lamellar crystallites which have twisting correlation along the radial axis.3-10 Concerned with the origin of the torsional stress, folded chains in the upper and lower surface regions of lamellar crystals are supposed to give rise to a residual asymmetric stress which has non-zero component of the torsional stress. The stress is called unbalanced surface stresses 11 and can get stronger by the reorganization of folding surfaces with lamellar thickening.12 The molecular origin of the torsional stress is therefore dependent on the specific nature of each polymer, such as molecular chirality 13 or asymmetric higher-order structures of the crystals. 14,15 In our recent studies, we have been focusing not on the molecular origin of the inherent stress but on the mechanism of the structural formation of spherulites in a mesoscopic scale, i.e., the mechanism of branching and re-orientation of lamellar crystals in the spherulites. We have examined the banded spherulites of polyethylene and non-banded spherulites of polybutene-1 in our recent studies. 16,17 The present paper is therefore for the further confirmation of the following proposed mechanism on the banded spherulites of poly(vinylidene fluoride), PVDF.In our proposed modeling of the branching and reorientation of lamellar crystals, we have suggested the possibility of a splaying instability of the growth front as the source of branching; the lateral width of each lamellar crystal is limited at a critical width, i.e., maximum lateral width, above which the crystal splays into branches. After the branching, the branches will be spontaneously re-oriented due to torsional inherent stress in the case of banded spherulites. Then, the reorientation results in the independent growth...

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Section: 2mentioning

confidence: 54%

Section: 2mentioning

confidence: 99%

mentioning

confidence: 99%

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Branching and Higher Order Structure in Banded Poly(vinylidene fluoride) Spherulites

Toda

Taguchi

Hikosaka

et al. 2008

Polym J

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“…This leads to poor cooperative packing of twisting lamellae and probably results in the irregular banded structure at high temperatures. Toda et al [50][51][52] have systematically revealed the role of macro screw dislocations in lamellar branching in the banded polymer spherulites.…”

Section: Organization Of Twisted Lamellae In Banded Spherulitesmentioning

confidence: 99%

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Zhang

et al. 2017

Crystals

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Abstract:In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under atomic force microscopy unveiled the fine details of lamellar twisting and branching in the banded spherulites of poly(R-3-hydroxybutyrate-co-17 mol % R-3-hydroxyhexanoate). Organization of the twisting lamellar crystals in the banded spherulites was revealed as well. The lamellar crystals change the orientation via twisting rather than the macro screw dislocations. In fact, macro screw dislocation provides the mechanism of synchronous twisting of neighboring lamellar crystals. The driving force of lamellar twisting is attributed to the anisotropic and unbalanced surface stresses. Besides molecular chirality, variation of the growth axis and the chemical groups on lamellar surface can change the distribution of the surface stresses, and thus may invert the handedness of lamellar twisting. Thus, based on both experimental results and physical reasoning, the relation between crystal chirality and chemical molecular structures has been suggested, via the bridge of the distribution of surface stresses. The factors affecting band spacing are briefly discussed. Some remaining questions and the perspective of the topic are highlighted.Keywords: banded polymer spherulite; ringed spherulite; lamellar twisting; organization of lamellar crystals; surface stresses; chirality When crystallized from quiescent melt or concentrated solution, polymer chains usually form spherulites consisted of multiple lamellar crystals radiating from the spherulite center. Observed under polarized optical microscope (POM), a spherulite shows the characteristic Maltese-cross extinction. Besides the Maltese cross, some spherulites demonstrate alternative bright and dark bands under POM. These spherulites are termed as banded spherulites or ringed spherulites. The band structure with different light intensities may result from different thicknesses or different birefringences but similar thickness. In the former case, the bands are due to the periodical modulation of sample thickness and there is no variation of refractive index in the spherulite. These nonbirefringent banded spherulites have been observed in some polymer single crystals formed from thin melt films [1] or solutions [2] and are reviewed by Li et al. [3] in this special issue. In the latter case, the birefringent bands can result from the wavy bending growth or twisting growth of crystals. The wavy bands have been reported in sheared liquid crystals [4,5], which do not form spherulites under the condition. In this mini-review, we focus on the birefringent banded spherulites, which consist of synchronously twisted lamellar crystals. The organization of the twisted lamellar crystals in the banded spherulites and the driving force for lamell...

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“…[99,165,167,267,[274][275][276] Allgemein ist noch keine Theorie der Organisation verwundener Lamellen in Sphärolithen verfügbar. Aus Beobachtungen an Poly(l-milchsäure), [120] Poly(ethylen), [124,125] Poly(R-3-hydroxybutyrat) [148] und Poly(vinylidenfluorid) [166] sowie aus unseren eigenen Beobachtungen an Mannit und Tetraphenylblei (Abbildung 1 f) ist bekannt, dass gut organisierte gebänderte Muster nur bei kleinen Verwindungsperioden entstehen. Starke Verwindung scheint alle anderen Inhomogenitäten zu unterdrücken.…”

Section: Morphologie Von Individuenunclassified

Wachstumsinduziertes Biegen und Verwinden von Einkristallen

et al. 2014

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Kristalle von verschiedenen Stoffen, z. B. von Elementen, Mineralien, einfachen Salzen, organischen Molekülkristallen und hochmolekularen Polymeren, können die Translationsfernordnung aufgeben, indem sie sich während des Wachstums verwinden und verbiegen. Diese Erscheinungen wurden bei Kristallen im Größenbereich von Nano‐ bis Zentimetern beobachtet. Wir analysieren, wie und warum viele Materialien solche oft drastischen nichtkristallographischen Verzerrungen wählen und betonen dabei die Kristallchemie, die zu Spannungen an Oberflächen von Kristalliten oder innerhalb des Volumens führt.

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Branching and Higher Order Structure in Banded Polyethylene Spherulites

Cited by 81 publications

References 72 publications

Branching and Higher Order Structure in Banded Poly(vinylidene fluoride) Spherulites

Branching and Higher Order Structure in Banded Poly(vinylidene fluoride) Spherulites

Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review

Wachstumsinduziertes Biegen und Verwinden von Einkristallen

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