Molecular dynamics simulations of nucleation details in stretched polyethylene

Liu, Zongfa; Zhou, Zhiping; Ming, Yongqiang; Zhang, Shuihua; Hao, Tongfan; Nie, Yijing

doi:10.1016/j.polymer.2020.122442

Cited by 26 publications

(46 citation statements)

References 67 publications

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“…Liu and co‐workers studied the nucleation details by stretching the same monodisperse PE systems to different strains using MD simulations. They observed a multistep nucleation process focusing mainly on the nucleation and crystallization process of the stretched PE 29 . Sliozberg and co‐workers studied ordering and crystallization of entangled PE melts under uniaxial tension using different strain rates as well, showing that chain ends are expelled from nascent polymer crystals 30 .…”

Section: Previous Work On Crystallizationmentioning

confidence: 99%

Molecular dynamics simulations of stretch‐induced crystallization in layered polyethylene

Romanos

Megariotis

Theodorou

2021

Polymer Crystallization

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We study, via united atom molecular dynamics (MD) simulations, the crystallization of six polyethylene (PE) systems, each consisting of alternating layers of molten linear polymer of two different degrees of polymerization, under stretch, while at the same time comparing against the corresponding results from two homogeneous monodisperse systems. The “slab,” out of which the model bidisperse layered systems are formed by applying periodic boundary conditions, is comprised of two different molten film subsystems, both of initial thickness 3.66 nm in the z‐direction, adhering to each other; in the first the chain length is 200 carbon atoms and in the second 400 carbon atoms. Following a short pre‐equilibration at 350 K and 1 bar, a stretching simulation is conducted in the NėxxLyPzzT ensemble, with the engineering strain rate ėxx fixed in the machine (pulling) direction x, parallel to the interfaces; the width of the films Ly fixed in the transverse direction; and the pressure Pzz normal to the interfaces fixed at 1 bar. The temperature during stretching is held constant at T = 300 K, corresponding to more than 100 K subcooling for both molar masses. Deformation to a stretch ratio of Lxx/Lxx,0 = 2.6 within 120 ns is followed by annealing according to two different protocols. In the first protocol, stretching is stopped and the systems allowed to relax in the NLxLyPzzT ensemble under Pzz = 1 bar for 60 ns. In the second protocol, stretching is continued at a rate 10 times lower than the initial one for 60 ns and then stopped, letting the systems relax for 100 ns. Crystallization is observed following both protocols. A nucleus of ordered material emerges early on during the first stage of stretching at a deformation rate of 0.05 nm/ns. The crystalline structure is sharper and more extended following the second, slower protocol. Crystallized macromolecules lie in planes almost parallel to the interface, forming a tilt angle of 20° to 24° with the pulling direction. Long and short chains co‐crystallize into lamellae, which are slightly more extended in the long‐chain regions. This study sheds light on the morphology expected to be developed in monomaterial packaging consisting of oriented bidisperse PE layers, designed to combine low permeability with recyclability and low‐environmental impact.

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Section: Previous Work On Crystallizationmentioning

confidence: 99%

Molecular dynamics simulations of stretch‐induced crystallization in layered polyethylene

Romanos

Megariotis

Theodorou

2021

Polymer Crystallization

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“…Due to the limitation of the experimental observation scale, the micro crystallization process of cyclic polymer and the carbon nanotube‐grafted molecular chains blend system has not been observed, such as the micro mechanism of molecular chains dynamic behaviors, nucleation and crystal growth have not been revealed. Nowadays, computer simulation can effectively describe the structural characteristics and mechanical properties of materials at the micro‐scale, and then reveal the relationship between the microstructure and macro properties of polymer materials 34–43 . Previously, our research group has successfully studied the nucleation process of polyethylene systems by using molecular dynamics simulations, and revealed the microscopic mechanism of the formation of precursors by the aggregation of oriented segments with trans conformation in local regions 34 .…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulation on the crystallization behavior of cyclic polyethylene affected by functionalized carbon nanotubes

Wei

Zhou

Hao

et al. 2022

J of Applied Polymer Sci

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In this work, the effects of functionalized carbon nanofillers (i.e., CNT‐g‐PE prepared by carbon nanotubes grafted with linear polyethylene) on the crystallization of cyclic polyethylene were revealed by molecular dynamics simulation, and compared with that of pure cyclic polyethylene(C‐PE) and carbon nanotube / cyclic polyethylene blends(C‐PE/CNT). The simulation results show that the CNT‐g‐PE has an anti‐nucleation effect on the cyclic polyethylene, the crystallinity and crystallization rate of the C‐PE/CNT‐g‐PE system are significantly lower than those of the other systems. This phenomenon can be explained by the topological effect when linear polyethylene chains grafted on carbon nanotubes are mixed with cyclic polyethylene. It is observed from the micro‐scale that when the linear polyethylene chains are in contact with cyclic polyethylene, the cyclic chains are passed through by the linear chains to form a transient entanglement network, further affecting the dynamic process of the molecular chains. The diffusion and orientation of the cyclic polyethylene molecular chain are inhibited. This limits the crystal nucleation efficiency and growth kinetics. These simulation results not only support some experimental findings, but also confirm some microscopic phenomena that are difficult to observe in the experiment, which provides some inspirations for the experimental design of high‐performance nanocomposite materials.

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“…Nowadays, with the fast developments of computer technology, computer simulation has been widely used in scientific researches. Some research groups have studied the crystallization behaviors of various polymers based on molecular simulations, and discovered interesting phenomena that are difficult to observe in experiments 44–51 . For instance, Gee et al used MD simulations to investigate the structural changes of polymer melts in the early ordering stages before crystallization, and successfully observed the spinodal phase separation preceding polymer crystallization 52 .…”

Section: Introductionmentioning

confidence: 99%

“…Some research groups have studied the crystallization behaviors of various polymers based on molecular simulations, and discovered interesting phenomena that are difficult to observe in experiments. [44][45][46][47][48][49][50][51] For instance, Gee et al used MD simulations to investigate the structural changes of polymer melts in the early ordering stages before crystallization, and successfully observed the spinodal phase separation preceding polymer crystallization. 52 Compared with experimental researches, molecular simulations provide the possibility to directly explore the details of molecular motions, and thus it can also be used to study the formation mechanisms of nanohybrid structures in polymer nanocomposites.…”

mentioning

confidence: 99%

Simulations on polymer nanocomposite crystallization

Liu

Nie

Ming

et al. 2021

Polymer Crystallization

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Polymer nanocomposites are widely used in industry due to their excellent mechanical properties. Polymer crystallization in polymer nanocomposites can effectively enhance the interfacial interactions between polymer matrix and nanofillers, thereby providing new ideas for preparing high-performance polymer materials. In recent years, molecular simulation has gradually become a powerful research tool for the investigation of polymer materials and physics. In this article, the latest simulation research progress on the crystallization behaviors of polymer nanocomposites under different conditions is reviewed, and the influences of various factors on the crystallization behaviors of homopolymers, copolymers, and oriented polymers filled with nanofillers, as well as polymers grafted on nanofillers are summarized and discussed.It is highly expected that the current review can supply some new insights into the development and design of new nanohybrid structures and then the control of the physical properties of polymer nanocomposites.

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Molecular dynamics simulations of nucleation details in stretched polyethylene

Cited by 26 publications

References 67 publications

Molecular dynamics simulations of stretch‐induced crystallization in layered polyethylene

Molecular dynamics simulations of stretch‐induced crystallization in layered polyethylene

Molecular dynamics simulation on the crystallization behavior of cyclic polyethylene affected by functionalized carbon nanotubes

Simulations on polymer nanocomposite crystallization

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