Molecular Conformation at the Crystal–Amorphous Interface in Polyethylene

Savage, Rebecca C.; Mullin, Nic; Hobbs, Jamie K.

doi:10.1021/ma5025736

Cited by 49 publications

(66 citation statements)

References 30 publications

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“…The PE sample used for high-resolution imaging was prepared by the procedure published by Mullin and Hobbs. 35 A small amount of 82.9 kDa polyethylene (PSS-pe83k, Polymer Standards Service USA, Amherst, MA) was heated on a glass slide and then mechanically sheared as the sample cooled 24 c. Polydimethylsiloxane (PDMS)…”

Section: B Polyethylene (Pe)mentioning

confidence: 99%

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

et al. 2017

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Tapping mode atomic force microscopy (AFM), also known as amplitude modulated (AM) or AC mode, is a proven, reliable and gentle imaging mode with widespread applications. Over the several decades that tapping mode has been in use, quantification of tip-sample mechanical properties such as stiffness has remained elusive. Bimodal tapping mode keeps the advantages of single-frequency tapping mode while extending the technique by driving and measuring an

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Section: B Polyethylene (Pe)mentioning

confidence: 99%

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

et al. 2017

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“…Thus, their accurate determinations have been key to revealing the relationship between structure and properties. Generally, they can be determined by atomic force microscopy (AFM) (Mullin & Hobbs, 2011;Savage et al, 2015;Wang et al, 2018) and transmission electron microscopy (TEM) (Rastogi et al, 1997;Maiti et al, 2000;Yamada et al, 2003) in real space, or smallangle X-ray scattering (SAXS) in reciprocal space (Strobl & Schneider, 1980;Hashida et al, 2010;Wang et al, 2014). Compared with AFM and TEM, SAXS has been the most powerful tool to observe structural evolution on the nanoscale, due to its higher time-resolving capability and lower requirements for sample preparation.…”

Section: Introductionmentioning

confidence: 99%

A new small-angle X-ray scattering model for polymer spherulites with a limited lateral size of the lamellar crystals

Li¹,

Ding²,

Liu³

et al. 2019

Int Union Crystallogr J

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As is well known, polymers commonly form lamellar crystals, and these assemble further into lamellar stacks and spherulites during quiescent crystallization. Fifty years ago, Vonk and Kortleve constructed the classical small-angle X-ray scattering theory (SAXS) for a lamellar system, in which it was assumed that the lamellar stack had an infinite lateral size [Vonk & Kortleve (1967), Kolloid Z. Z. Polym. 220, 19–24]. Under this assumption, only crystal planes satisfying the Bragg condition can form strong scattering, and the scattering from the lamellar stack arises from the difference between the scattering intensities in the amorphous and crystalline layers, induced by the incident X-ray beam. This assumption is now deemed unreasonable. In a real polymer spherulite, the lamellar crystal commonly has dimensions of only a few hundred nanometres. At such a limited lateral size, lamellar stacks in a broad orientation have similar scattering, so interference between these lamellar stacks must be considered. Scattering from lamellar stacks parallel to the incident X-ray beam also needs to be considered when total reflection occurs. In this study, various scattering contributions from lamellar stacks in a spherulite are determined. It is found that, for a limited lateral size, the scattering induced by the incident X-ray beam is not the main origin of SAXS. It forms double peaks, which are not observed in real scattering because of destructive interference between the lamellar stacks. The scattering induced by the evanescent wave is the main origin. It can form a similar interference pattern to that observed in a real SAXS measurement: a Guinier region in the small-q range, a signal region in the intermediate-q range and a Porod region in the high-q range. It is estimated that, to avoid destructive interference, the lateral size needs to be greater than 11 µm, which cannot be satisfied in a real lamellar system. Therefore, SAXS in a real polymer system arises largely from the scattering induced by the evanescent wave. Evidence for the existence of the evanescent wave was identified in the scattering of isotactic polypropylene. This study corrects a long-term misunderstanding of SAXS in a polymer lamellar system.

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“…The model in Fig. 6B may seem to lack the roughness of crystallite surfaces observed experimentally (37). We propose that chain ends are only moderately disordered because we attribute the roughness mostly to the complex connectivity of chains across the crystallinenoncrystalline interface, resulting in tight folds for adjacent reentry, loops for nonadjacent reentry, entangled loops, tie molecules, crowding problems (1), etc.…”

Section: Probing the Spatial Distribution Of Chain Ends By 1 H And 13mentioning

confidence: 87%

Immobilized ¹³ C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR

Yuan

Schmidt‐Rohr

2020

Sci. Adv.

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A comprehensive 13C nuclear magnetic resonance (NMR) approach for characterizing the location of chain ends of polyethers and polyesters, at the crystallite surface or in the amorphous layers, is presented. The OH chain ends of polyoxymethylene are labeled with 13COO-acetyl groups and their dynamics probed by 13C NMR with chemical shift anisotropy (CSA) recoupling. At least three-quarters of the chain ends are not mobile dangling cilia but are immobilized, exhibiting a powder pattern characteristic of the crystalline environment and fast CSA dephasing. The location and clustering of the immobilized chain ends are analyzed by spin diffusion. Fast 1H spin diffusion from the amorphous regions shows confinement of chain ends to the crystallite surface, corroborated by fast 13C spin exchange between chain ends. These observations confirm the principle of avoidance of density anomalies, which requires that chains terminate at the crystallite surface to stay out of the crowded interfacial layer.

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Molecular Conformation at the Crystal–Amorphous Interface in Polyethylene

Cited by 49 publications

References 30 publications

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

A new small-angle X-ray scattering model for polymer spherulites with a limited lateral size of the lamellar crystals

Immobilized ¹³ C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR

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Molecular Conformation at the Crystal–Amorphous Interface in Polyethylene

Cited by 49 publications

References 30 publications

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

Fast, High Resolution, and Wide Modulus Range Nanomechanical Mapping with Bimodal Tapping Mode

A new small-angle X-ray scattering model for polymer spherulites with a limited lateral size of the lamellar crystals

Immobilized 13 C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR

Contact Info

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Resources

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Immobilized ¹³ C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR