Monte Carlo Simulation of Short Chain Branched Polyolefins in the Molten State

Ramos, Javier; Peristeras, Loukas D.; Theodorou, Doros N.

doi:10.1021/ma071615k

Cited by 93 publications

(134 citation statements)

References 43 publications

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“…The density profile within the interface for the linear PE system using the TraPPE-UA force field was slightly higher than that obtained using the PYS force field, while the density in the fully amorphous region was cor-respondingly a few percent lower, consistent with the results of Ramos et al for the amorphous melts. 48 In Fig. 3 we present the orientational order (P 2 ) profile along the z-axis for all of the systems.…”

Section: Resultsmentioning

confidence: 99%

“…Growing the branch site-by-site in this fashion introduced a bias that must be removed by including the corresponding Rosenbluth weight 47 in the final acceptance criterion for the trial branch, bonded interactions in the acceptance criteria also included the LJ interaction due to the mutation of both the old and new branch sites. In this work, a value of k=6 was used, as recommended by Ramos et al 48 For a typical production run at T=350K, the acceptance ratio of the branch migration move for systems containing methyl, ethyl or butyl branches was 0.48, 0.20 or 0.03, respectively.…”

Section: Methodmentioning

confidence: 99%

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Effect of Short Chain Branching on the Interlamellar Structure of Semicrystalline Polyethylene

2017

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We use molecular simulations with a united atom force field to examine the effect of short chain branching (SCB) on the noncrystalline, interlamellar structure typical of linear low density polyethylene (LLDPE). The model is predicated on a metastable thermodynamic equilibrium within the interlamellar space of the crystal stack and accounts explicitly for the various chain topologies (loops, tails, and bridges) therein. We examine three branched systems containing methyl, ethyl, and butyl side branches, and compare our results to high density polyethylene (HDPE), without branches. We also compare results for two united atom force fields, PYS and TraPPE-UA, within the context of these simulations. In contrast to conventional wisdom, our simulations indicate that the thicknesses of the interfacial regions in systems with SCB are smaller than those observed for a linear polyethylene without branches, and that branches are uniformly distributed throughout the interlamellar region. We find a prevalence of gauche states along the backbone due to the presence of branches, and an abrupt decrease in the orientational order in the region immediately adjacent to the crystallite.3 Introduction:

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Section: Resultsmentioning

confidence: 99%

Section: Methodmentioning

confidence: 99%

Effect of Short Chain Branching on the Interlamellar Structure of Semicrystalline Polyethylene

2017

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“…The self-diffusion coefficients, D 62,63 For each data point, atomic overlaps were eliminated by applying a conjugate gradient energy minimization method of 10 5 steps, followed by a short simulation of 5 ns in the canonical ensemble (NVT). A 25 ns simulation in the isobaric-isothermal ensemble (NPT) was then conducted and afterwards simulations of 20 ns were performed in the canonical ensemble (NVT) at the mean density, as obtained from the NPT simulations.…”

Section: Self-diffusion Coefficientsmentioning

confidence: 99%

Thermophysical properties of imidazolium tricyanomethanide ionic liquids: experiments and molecular simulation

Zubeir

Rocha

Vergadou

et al. 2016

Phys. Chem. Chem. Phys.

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The low-viscous tricyanomethanide ([TCM]À )-based ionic liquids (ILs) are gaining increasing interest as attractive fluids for a variety of industrial applications. The thermophysical properties (density, viscosity, surface tension, electrical conductivity and self-diffusion coefficient) of the 1-alkyl-3-methylimidazolium tricyanomethanide [C n mim][TCM] (n = 2, 4 and 6-8) IL series were experimentally measured over the temperature range from 288 to 363 K. Moreover, a classical force field optimized for the imidazolium-based[TCM] À ILs was used to calculate their thermodynamic, structural and transport properties (density, surface tension, self-diffusion coefficients, viscosity) in the temperature range from 300 to 366 K. The predictions were directly compared against the experimental measurements. The effects of anion and alkyl chain length on the structure and thermophysical properties have been evaluated. In cyano-based ILs, the density decreases with increasing molar mass, in contrast to the behavior of the fluorinated anions, being in agreement with the literature. The contribution per -CH 2 -group to the increase of the viscosity presents the following sequence: The experimentally determined self-diffusion coefficients of the cations are in good agreement with the molecular simulation predictions, in which a decrease of the self-diffusion of the cations with increasing alkyl chain length is observed with a simultaneous increase in viscosity and for the longer alkyl lengths the anion becomes more mobile than the cation.

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“…We mainly focus our attention on the ability of each FF to simulate complex phenomena as melt dynamics, glass transition and crystallization process. There are various reasons for choosing C 192 model: (i) the entanglement length of PE is about 60−160 carbons as determined by experiments and simulations 26 44 and of the crystallization and melting behavior of similar n-alkanes and PE samples. 39−43 The paper is organized as follows.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations for the Description of Experimental Molecular Conformation, Melt Dynamics, and Phase Transitions in Polyethylene

2015

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Long molecular dynamics simulations of the melt dynamics, glass transition and nonisothermal crystallization of a C 192 polyethylene model have been carried out. In this model, the molecules are sufficiently long to form entanglements in the melt and folds in the crystalline state. On the other hand, the molecules are short enough to enable the use of atomistic simulations on a large scale of time. Two force fields, widely used for polyethylene, are taken into account comparing the simulation results with a broad set of literature experimental data. Although both force fields are able to capture the general physics of the system, TraPPe-UA is in a better quantitative agreement with the experimental data. According with the simulation results some fundamental aspects of polyethylene physical parameters are discussed such as the characteristic ratio (C n = 8.2 and 7.6 at 500 K, for TraPPe-UA and PYS force fields, respectively), the isothermal compressibility (α = 8.57 × 10 −4 K −1 ), the static structure factor and the melt dynamics regimes corresponding to an entangled polymer. Furthermore, the simulated T g (187.0 K) obtained for linear PE is in a very good agreement with the extrapolated T g values (185−195 K) using the Gordon−Taylor equation. Finally, the simulation of the nonisothermal crystallization process supports the view of a mixed state of adjacent and nonadjacent re-entry model. The simulated two phase model reproduces very well the initial fold length expected for high supercoolings and the segregation of the system in ordered and disordered layers. The paper highlights the importance of combining simulation techniques with experimental data as a powerful means to explain the polymer physics.

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Monte Carlo Simulation of Short Chain Branched Polyolefins in the Molten State

Cited by 93 publications

References 43 publications

Effect of Short Chain Branching on the Interlamellar Structure of Semicrystalline Polyethylene

Effect of Short Chain Branching on the Interlamellar Structure of Semicrystalline Polyethylene

Thermophysical properties of imidazolium tricyanomethanide ionic liquids: experiments and molecular simulation

Molecular Dynamics Simulations for the Description of Experimental Molecular Conformation, Melt Dynamics, and Phase Transitions in Polyethylene

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