Roughening Transition and Quasi-continuous Melting of Monolayers of Ultra-long Alkanes: Why Bulk Polymer Melting Is Strongly First-Order

Zhang, Ruibin; Fall, William S.; Hall, Kyle Wm.; Gehring, G. A.; Zeng, Xiangbing; Ungar, Goran

doi:10.1021/acs.macromol.1c01377

Cited by 8 publications

(6 citation statements)

References 70 publications

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“…Evaluating the overall crystallinity of each system requires a suitably defined order parameter. Previous studies of PE have employed the second Legendre polynomial, ,,,,, defined as P 2 = (3⟨cos 2 θ i , j ⟩ – 1)/2, where θ i , j is the angle between the backbone of two given CG beads and the angular brackets indicate averaging over all beads within a predefined cutoff distance r c ; for details, see the Supporting Information. The second minimum of the radial distribution function is used as the cutoff distance (∼1.6σ) corresponding to the next nearest neighbor; see Figure S3.…”

Section: Methodsmentioning

confidence: 99%

Role of Short Chain Branching in Crystalline Model Polyethylenes

et al. 2022

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The role of short chain branches (SCBs) (C4H9) on the melt and crystalline properties of monodisperse polyethylene systems (C400H802) is investigated, using molecular dynamics simulations of a coarse-grained united-monomer model that represents a chemical monomer as one particle. A method is introduced, whereby SCBs are grown out of the linear backbone to minimize computational expense. Here, this concept is proven by introducing differing numbers (N b = 0, 1, 2, 4, 10, and 20) of regularly spaced SCBs along the chain backbones and studying their influence on the melt and crystalline properties. By growing SCBs into the melt phase, it is demonstrated that they marginally perturb the original topology, justifying a relatively short equilibration time after growth. Upon crystallization, however, each system’s behavior differs considerably. Cooling and heating cycles are performed to study crystallization and melting at progressively slower rates. The crystalline morphology is observed to depend strongly on both cooling rate and number of branches along the linear backbone. In particular, the lamella thickness decreases systematically with both faster cooling and increasing SCB content. At the highest branch content, of one per 20 backbone carbons (N b = 20), crystallization is almost entirely suppressed, whereas a small number of branches allows control over the average lamellar thickness. This observation, combined with a prudent method for equilibrating systems with SCBs, opens up opportunities to study more complex chain architectures and mimic industrial polyethylene morphologies.

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Section: Methodsmentioning

confidence: 99%

Role of Short Chain Branching in Crystalline Model Polyethylenes

et al. 2022

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“…To further interrogate the morphology of the different crystalline forms, the stem length distribution and structure factors are examined in Figure . Stem length distributions are calculated by examining the local alignment of bond vectors using the local P 2 order parameter, commonly employed to assess the crystallinity in simulations of PE crystallization, ,,,, which may be defined as P 2 = ⟨ 3 ⁡ cos 2 ⁡ θ i , j − 1 2 ⟩ where θ i , j is the angle between an arbitrary bond i with all neighboring bonds j in the immediate vicinity. The neighboring cutoff is chosen identical to our previous work, for further details see ref .…”

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confidence: 99%

“…19 To further interrogate the morphology of the different crystalline forms, the stem length distribution and structure factors are examined in Figure 4. Stem length distributions are calculated by examining the local alignment of bond vectors using the local P 2 order parameter, commonly employed to assess the crystallinity in simulations of PE crystallization, 2,13,14,19,33 which may be defined as…”

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confidence: 99%

Molecular Simulations of Controlled Polymer Crystallization in Polyethylene

et al. 2023

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Multilamella polymer crystals are grown from the melt for the first time, in molecular dynamics simulations of a united-monomer model, with in excess of 1500000 unitedmonomers. Two-component systems comprised of equal weight fractions of 2000 united-monomer long chains and 200 unitedmonomer short chains are considered, with varying numbers of short butyl branches placed along the long chains. Utilizing two different cooling protocols, continuous-cooling and self-seeding, drastically different multilamella structures are revealed, which depend heavily on the branch content and crystallization protocol used. By self-seeding, well-aligned multilamella crystals are grown, which more clearly reveal the subtle alterations an increasing number of branches create on the size and shape of the crystallites in the early stages of spherulite formation. Under continuous cooling, this observation is almost completely obscured. At maximum thickness, chain portions as long as 100 united-monomers (200 carbons) are extended inside the crystalline lamella.

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“…Adjacent all‐trans methylene groups in PA 66 α ‐phase are 0.254 nm apart, while the centers of two neighboring six‐membered rings of CNT are 0.246 nm apart. [ 39 ] For the remainder of the studies, CNT loading levels of 0.01%, 0.1%, and 1% CNT will be analyzed, as isothermal crystallization kinetics show 1% CNT is above the saturation limit for crystallization. Non‐isothermal crystallization was analyzed at cooling rates ranging from 1 to 4000 K s −1 in the quiescent nanocomposite systems.…”

Section: Resultsmentioning

confidence: 99%

Competition between Heterogeneous Nucleation and Flow‐Induced Crystallization of Polyamide 66 and Its Carbon Nanotube Composites

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Zhang

McHale

et al. 2022

Macromol. Rapid Commun.

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Both heterogeneous nucleation and flow‐induced entropy reduction are the two well‐known factors that accelerate polymer crystallization. However, the interplay of nucleation and flow‐induced acceleration is still poorly understood. This work investigates the nucleating effect of carbon nanotubes (CNT) on both the quiescent and flow‐induced crystallization kinetics of polyamide 66 (PA 66). The quiescent crystallization study indicates that CNT acts as a powerful nucleant, as suggested by the fact that the critical cooling rate to bypass crystallization and create the amorphous glassy state changes from 1000 K s−1 in PA 66 neat resin to a rate faster than 4000 K s−1 in the PA 66 nanocomposites. The flow‐induced crystallization study indicates PA 66 onset crystallization time and morphology depend on the shear work introduced by rotational rheometry. A combined acceleration effect from CNT nucleants and flow‐induced crystallization (FIC) persists when the CNT loading is under the saturation limit. However, if CNT loading meets the saturation limit, specific shear work shows no impact on the crystallization time, providing evidence that the role of the FIC acceleration effect no longer exists when nucleant acceleration dominates the crystallization of PA 66.

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Roughening Transition and Quasi-continuous Melting of Monolayers of Ultra-long Alkanes: Why Bulk Polymer Melting Is Strongly First-Order

Cited by 8 publications

References 70 publications

Role of Short Chain Branching in Crystalline Model Polyethylenes

Role of Short Chain Branching in Crystalline Model Polyethylenes

Molecular Simulations of Controlled Polymer Crystallization in Polyethylene

Competition between Heterogeneous Nucleation and Flow‐Induced Crystallization of Polyamide 66 and Its Carbon Nanotube Composites

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