Strong memory of strain-induced copolymer crystallization as revealed by Monte Carlo simulations

Guan, Xinchao; Gao, Huanhuan; Zha, Liyun; Wu, Yixian; Hu, Wenbing

doi:10.1016/j.polymer.2016.06.040

Cited by 22 publications

(14 citation statements)

References 19 publications

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“…The lower the value of T s , the higher is the T c upon cooling from the melt, indicating a stronger nucleation effect. This peculiar nucleation effect has been termed in different ways in the literature: crystalline memory, ,,,− ,,,− melt memory, ,,,,− in some works both terms are used indistinctly, ,,,,,− and in other cases a more general term, memory effect, has been employed. ,,,− ,,− In this Perspective, we will use the term melt memory to emphasize that this effect occurs when, according to calorimetric evidence, there are no crystal fragments present in the melt (i.e., in the so-called Domain IIa ; see section ).…”

Section: Introduction and Phenomenology Of Self-nucleation And Melt M...mentioning

confidence: 99%

Self-Nucleation Effects on Polymer Crystallization

2020

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The existence of a "memory" of the previous crystalline state, which survives melting and enhances re-crystallization kinetics by a self-nucleation process, is wellknown in polymer crystallization studies. Despite being extensively investigated, since the early days of polymer crystallization studies, a complete understanding of melt memory effects is still lacking. In particular, the exact constitution of self-nuclei is still under debate. In this perspective, we provide a comprehensive and critical overview of melt memory effects in polymer crystallization. After the phenomenology of the process and some key concepts are introduced, the main experimental results of the last decades are summarized. Analogies and discrepancies of the melt memory characteristics of different polymeric systems are highlighted. Based on this background, the most significant interpretations and theories of melt memory effects are described; underlining that different interpretations may apply to various specific cases. Recent insights on self-nucleation, gained thanks to a multi-technique approach (combining calorimetry, rheology, infrared and dielectric spectroscopy), are presented. The role of intra/inter-chain segmental contacts in the strength of melt memory effects, and the differences between homopolymers and copolymers behavior, are discussed. Finally, we identify areas where further research in the field is needed to shed light on the longstanding questions regarding the origin of melt memory effects in semi-crystalline polymers.

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Section: Introduction and Phenomenology Of Self-nucleation And Melt M...mentioning

confidence: 99%

Self-Nucleation Effects on Polymer Crystallization

2020

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“…In addition, both the enhanced nucleation and growth of shish-like elongated nuclei under sufficiently fast flows were investigated by Graham et al , Dynamic Monte Carlo (MC) simulations demonstrated that long chains retain the orientation memory after shear cessation, and crystallize into shish in priority, which will induce short-chain kebabs later on . In addition, dynamic MC simulations of strain-induced polymer crystallization have been performed, − which improved our substantial understanding on flow-induced polymer crystallization. On the other hand, dynamic MC simulations were also employed to investigate shear-stress-induced coil deformation in the driven flows. − …”

Section: Introductionmentioning

confidence: 99%

Shish-Kebab Crystallites Initiated by Shear Fracture in Bulk Polymers

et al. 2018

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The study of shear-induced polymer crystallization has so far overlooked heterogeneous crystal nucleation of shish-kebab crystallites, which can be initiated by the stretched local polymer chains in the sporadic events of shear fracture upon sudden startup or cessation of polymer shear flow or in the memory of these events. We performed dynamic Monte Carlo simulations of a binary blend of short and long polymers and investigated the formation process of shish-kebab crystallites in a driven field with Poiseuille-flow-like gradient forces presumably generated around the shear layer of melt fracture. The results demonstrated the synergetic coil-extension and segregation behaviors of long-chain fractions upon precursor formation, which lead to a discontinuous crystalline structure along the shish. We found that the shear fracture hypothesis can reconcile several controversial experimental arguments on the precursor formation of shish-kebab crystallites in shear-induced polymer crystallization.

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“…It is reasonable to assume that when the crystallites of ethylene copolymers melt, clusters from the initial crystalline ethylene sequences remain in close proximity, because segmental melt diffusion to randomize all sequences is hampered by branches and the constrained intercrystalline topology. Although these remains of sequence partitioning can be taken as a weak phase separation in the melt, melts with this type of memory are metastable systems where the clusters are effective pre‐nuclei that only fully dissolve into a homogeneous melt at temperatures well above the equilibrium melting point . Segmented thermoplastic polyurethanes are also examples of systems with sequence selective crystallization, and have also shown relatively strong melt memory …”

Section: Introductionmentioning

confidence: 99%

Effect of annealing time and molecular weight on melt memory of random ethylene 1‐butene copolymers

Chen

Alamo

2018

Polymer International

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The effects of annealing time and molecular weight on the strong melt memory effect observed in random ethylene 1‐alkene copolymers are analyzed in a series of model ethylene 1‐butene copolymers with 2.2 mol% branches. Melt memory is associated with molten clusters of ethylene sequences from the initial crystals that remain in close proximity and are unable to diffuse quickly to the randomized melt state, thus increasing the recrystallization rate. Melt memory persists even for greater than 1000 min annealing indicating a long‐lived nature of the clusters that only fully dissolve at melt temperatures above a critical value (>160 °C). Below the critical melt temperature, molecular weight and annealing temperature have a strong influence on the slow kinetics of melt memory. For the copolymers analyzed, slow dissolution of clusters is experimentally observed only for Mw < 50 000 g mol−1. More stable clusters that survive higher annealing temperatures display slower dissolution rates than clusters remaining at lower temperatures. The threshold crystallinity level to enable melt memory (Xc,threshold) decreases with increasing molecular weight and decreasing annealing temperature similarly to the variation of the chain diffusivity in the melt. The process leading to melt memory is thermally activated as the variation of Xc,threshold with temperature follows Arrhenius behavior with high activation energy (ca 108 kJ mol−1) that is independent of molecular weight. © 2018 Society of Chemical Industry

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Strong memory of strain-induced copolymer crystallization as revealed by Monte Carlo simulations

Cited by 22 publications

References 19 publications

Self-Nucleation Effects on Polymer Crystallization

Self-Nucleation Effects on Polymer Crystallization

Shish-Kebab Crystallites Initiated by Shear Fracture in Bulk Polymers

Effect of annealing time and molecular weight on melt memory of random ethylene 1‐butene copolymers

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