A challenging topic of computer simulations: Polymorphism in polymers

Luo, Chuanfu

doi:10.1002/pcr2.10109

Cited by 6 publications

(4 citation statements)

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“…Depending on processing conditions or thermal pathways, many crystallizable polymers have the ability to form various ordered structures, denoted as polymorphs and distinguished by differences in their crystal unit cell parameters. Within the different lattices, macromolecules may have the same or different stable conformations, characterizing packing or conformational polymorphism, respectively. − For example, poly(vinylidene fluoride) and isotactic polypropylene show five crystal forms, while isotactic poly(1-butene) exhibits at least four known structures. − …”

Section: Introductionmentioning

confidence: 99%

Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of Another One

et al. 2023

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We present investigations of the intricate crystallization and melting behavior of an alternating copolymer synthesized by photopolymerization of 2,2′-dimercaptodiethyl sulfide with di(ethylene glycol)divinyl ether. Upon increasing temperature, we observed the succession of two distinctly separated melting processes, which we related to the sequential formation and disappearance of two crystalline polymorphs. Due to their well-separated melting temperatures T m1 and T m2 , we labeled these polymorphs as LOW-T m -form and HIGH-T m -form, respectively. X-ray diffraction results confirmed differences in the parameters of the crystal unit cells. However, upon cooling from the isotropic melt, we never obtained the HIGH-T m -form and could only generate the LOW-T m -form characterized by spherulitic crystals that melted completely at T m1 . Surprisingly, simultaneously everywhere within these molten spherulites, a large number of needle-like crystals were growing as a function of the time the sample was kept (well) above T m1 . All crystals exhibited an orientation largely following the radial direction of the initial spherulites. This observation suggests that molten polymer chains remembered for some time their previous alignment within the crystalline LOW-T m -form. This memory assisted the nucleation and thus exclusively enabled the formation of the HIGH-T m -form. Only when partially crystallizing a sample aboveT m1 in the HIGH-T m -form and subsequently cooling it below T m1 allowed to achieve coexistence of both polymorphs. When heating such a sample of coexisting crystalline structures above T m1 , only the LOW-T m -form melted and the HIGH-T m -form remained. The generality of our findings has been demonstrated by similar results obtained for complementary alternating copolymers. Our study suggests that the otherwise impossible nucleation of polymorphs with a high melting temperature can be enabled by prior orientation of chains within another easily established polymorph characterized by a lower melting temperature.

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Section: Introductionmentioning

confidence: 99%

Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of Another One

et al. 2023

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“…Flow-induced polymorphism has been proved by recent works [80,83]. However, 'simulations on polymorphism in polymers is almost an untouched important topic so far' as described by Luo [212] in his recent perspective. For instance, various crystal structures of PE, i.e., hexagonal and orthorhombic [158,169], can be accurately predicted by modeling.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

“…But the micro-scale character makes it difficult to compare with experiments directly. For the bridging between MD and experiments, four main challenges need to be overcame, namely, high supercooling, polymorphism [212], high molecular weight and wide MWD [167].…”

Section: Comparison With Experimentsmentioning

confidence: 99%

“…For instance, the polymorphism of i-PP cannot be acquired in simulations with one more side methyl carbon added compared with PE. To solve this long-term challenge, accelerating algorithms, i.e., metadynamics and hybrid dynamics, may be a breakthrough [212], which is similar to that used in conquering the problem of supercooling.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

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Polymer crystallization under external flow

Sheng¹,

Chen²,

Cui³

et al. 2022

Rep. Prog. Phys.

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The general aspects of polymer crystallization under external flow, i.e., flow-induced crystallization (FIC) from fundamental theoretical background to multi-scale characterization and modeling results are presented. FIC is crucial for modern polymer processing, such as blowing, casting, and injection modeling, as two-third of daily-used polymers is crystalline, and nearly all of them need to be processed before final applications. For academics, the FIC is intrinsically far from equilibrium, where the polymer crystallization behavior is different from that in quiescent conditions. The continuous investigation of crystallization contributes to a better understanding on the general non-equilibrium ordering in condensed physics. In the current review, the general theories related to polymer nucleation under flow (FIN) were summarized first as a preliminary knowledge. Various theories and models, i.e., coil-stretch transition and entropy reduction model, are briefly presented together with the modified versions. Subsequently, the multi-step ordering process of FIC is discussed in detail, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline. These achievements for a thorough understanding of the fundamental basis of FIC benefit from the development of various hyphenated rheometer, i.e., rheo-optical spectroscopy, rheo-IR, and rheo-X-ray scattering. The selected experimental results are introduced to present efforts on elucidating the multi-step and hierarchical structure transition during FIC. Then, the multi-scale modeling methods are summarized, including micro/meso scale simulation and macroscopic continuum modeling. At last, we briefly describe our personal opinions related to the future directions of this field, aiming to ultimately establish the unified theory of FIC and promote building of the more applicable models in the polymer processing.

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Molecular Simulations of Polymer Crystallization

Nie

Jian-long

2023

Polymer Crystallization

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A challenging topic of computer simulations: Polymorphism in polymers

Cited by 6 publications

References 30 publications

Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of Another One

Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of Another One

Polymer crystallization under external flow

Molecular Simulations of Polymer Crystallization

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