Polymorphism and Melting in Crystalline Polyethylene and Alkanes: Molecular Dynamics Simulations

Zubova, E. A.

doi:10.1007/978-3-642-37179-0_29-1

Cited by 6 publications

(10 citation statements)

References 60 publications

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“…From the quiescent MD simulations of the entangled C 1000 H 2002 melt [50], the disengagement time τ d was determined as 5270 ns, the number of entanglements per chain) Z (via the Z1 code [63]) was 12.9, and the fully trans conformation chain end-to-end distance was 1290.2 Å. Toda [68] measured a melting point (T m ) of 398-403 K for quiescently grown single crystals of a linear PE with molar mass 13 600 g/mol, which is fairly close to the C 1000 H 2002 (M w = 14 002 g/mol) linear PE examined herein. Although it has thus far been impossible to determine a precise T m range for quiescent PE systems via MD, the accrued evidence to date suggests that a viable range would be 385-400 K [37,41,44,45,69]. Hence, the simulated melt temperature (450 K) used in this study is likely greater than 50 K above the values of T m as determined via experiment and equilibrium MD.…”

Section: Resultsmentioning

confidence: 84%

Flow-induced crystallization of a polyethylene liquid above the melting temperature and its nonequilibrium phase diagram

Sefiddashti

Edwards

Khomami

2020

Phys. Rev. Research

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Manufacturing of plastics is typically performed via flow processing of a polymer melt. Semicrystalline polymers, such as polyethylene (PE), play a critical role in the global plastics markets, but fundamental understanding of how process flow conditions affect their properties is lacking. Nonequilibrium molecular dynamics of a PE liquid above its melting point revealed reversible transitions from coiled, biphasic, stretched, pretransitional, and crystalline phases with applied stress in elongational flow. A nonequilibrium phase diagram was developed for the thermodynamic state space.

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Section: Resultsmentioning

confidence: 84%

Flow-induced crystallization of a polyethylene liquid above the melting temperature and its nonequilibrium phase diagram

Sefiddashti

Edwards

Khomami

2020

Phys. Rev. Research

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“…As seen in Figure , the temperature of the transition from the β to the condis phase in MD simulations ( T C ∼ 650 K) is approximately 2 times higher than the temperature where the maximal electrocaloric effect is experimentally observed for terpolymers ( T ∼ 300 K). Such a discrepancy in the MD prediction of the first-order phase transition temperature is known in the polymer literature and is partly attributed to the small time scale achieved in the MD simulation . That is, the expansion of the system with a subsequent phase transition requires a very long MD simulation time if the temperature is not much higher than the actual transition temperature.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Such a discrepancy in the MD prediction of the first-order phase transition temperature is known in the polymer literature and is partly attributed to the small time scale achieved in the MD simulation. 41 That is, the expansion of the system with a subsequent phase transition requires a very long MD simulation time if the temperature is not much higher than the actual transition temperature. Consequently, when heated, the system remains in the metastable β phase for a long time until the temperature reaches a high value, sufficient for a rapid transition to the condis phase.…”

Section: Model and Simulation Methodsmentioning

confidence: 99%

Microscopic Mechanism of the Large Electrocaloric Effect in Vinylidene Difluoride-Based Polymers

et al. 2021

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The molecular mechanism of the large electrocaloric effect in ferroelectric vinylidene difluoride-based polymers was proposed. The mechanism involves the electric field-induced phase transition between the ferroelectric β-phase and the paraelectric conformationally disordered (condis) phase. The condis phase is characterized by the absence of a three-dimensional crystallographic order: there is only two-dimensional translational symmetry in the plane perpendicular to the chain direction. Due to conformational disorder, the entropy of the condis phase is higher than that of the β-phase. A high entropy change at the transition from the β to the condis phase causes a large electrocaloric effect. Molecular dynamics simulations of the poly(vinylidene fluoride-co-trifluoroethylene) (poly(VDF-co-TrFE)) copolymer and poly(vinylidene fluoride–ter–trifluoroethylene–ter–chlorofluoroethylene) (poly(VDF-ter-TrFE-ter-CFE)) and poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) (poly(VDF-ter-TrFE-ter-CTFE)) terpolymers were performed. The electrocaloric effect was determined from simulations using two techniques: (i) direct calculation of the temperature drop in adiabatic conditions and (ii) calculation of the entropy difference between β and condis phases from the pair histograms of dihedral angles. Both techniques predict similar temperature drops that validate the proposed molecular mechanism.

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“…The polymorphism of PE has been studied by molecular modeling and all‐atom MD simulations based on experimental results . A recent all‐atom MD simulation studied the anomalous chain mobility in the condis phase of PE .…”

Section: Current Advances and The Futurementioning

confidence: 99%

“…However, most of the reported simulations studying polymer crystallization are based on models ignoring some molecular details to boost simulations, resulting in faster crystallization but incorrect crystalline structure. So far, the reported simulations of polymorphism in polymers are limited as few studies of PE using all‐atom models, of iPP using fine united‐atom or all‐atom models, and of molecular modelings of specific polymers with experimental data …”

Section: Introductionmentioning

confidence: 99%

A challenging topic of computer simulations: Polymorphism in polymers

Luo

2020

Polymer Crystallization

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To predict crystalline structures and respective mechanic properties of polymers are the long-term target of computer simulations. The simulation of polymorphism in polymers requires the all-atom model with proper force field. The all-atom model can provide correct crystalline structure and the respective properties, but results in extremely slow dynamics in simulations. The conventional molecular dynamics (MD) using the all-atom model could be applied to the study of polymorphism of simple polymers without side chain groups such as polyethylene. For more complex polymers with side chain groups, the conventional MD using the all-atom models are too slow and accelerating methods must be used to boost the slow chain dynamics. The metadynamics and hybrid dynamics might be used in the future simulations of polymorphism. K E Y W O R D S all-atom model, computer simulation, hybrid dynamics, metadynamics, polymer crystallization, polymorphism

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Polymorphism and Melting in Crystalline Polyethylene and Alkanes: Molecular Dynamics Simulations

Cited by 6 publications

References 60 publications

Flow-induced crystallization of a polyethylene liquid above the melting temperature and its nonequilibrium phase diagram

Flow-induced crystallization of a polyethylene liquid above the melting temperature and its nonequilibrium phase diagram

Microscopic Mechanism of the Large Electrocaloric Effect in Vinylidene Difluoride-Based Polymers

A challenging topic of computer simulations: Polymorphism in polymers

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