scholarly journals Monodisperse Polymer Melts Crystallize via Structurally Polydisperse Nanoscale Clusters: Insights from Polyethylene

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 447 ◽  
Author(s):  
Kyle Wm. Hall ◽  
Timothy W. Sirk ◽  
Simona Percec ◽  
Michael L. Klein ◽  
Wataru Shinoda
Keyword(s):  
Large Scale ◽  
Polymer Melts ◽  
Polymeric Materials ◽  
Crystalline Polymer ◽  
Crystal Nucleation ◽  
Stem Length ◽  
Polymer Crystal ◽  
Polyethylene Melts ◽  
Nanoscale Clusters ◽  
Entangled Polymer Melts

This study demonstrates that monodisperse entangled polymer melts crystallize via the formation of nanoscale nascent polymer crystals (i.e., nuclei) that exhibit substantial variability in terms of their constituent crystalline polymer chain segments (stems). More specifically, large-scale coarse-grain molecular simulations are used to quantify the evolution of stem length distributions and their properties during the formation of polymer nuclei in supercooled prototypical polyethylene melts. Stems can adopt a range of lengths within an individual nucleus (e.g., ∼1–10 nm) while two nuclei of comparable size can have markedly different stem distributions. As such, the attainment of chemically monodisperse polymer specimens is not sufficient to achieve physical uniformity and consistency. Furthermore, stem length distributions and their evolution indicate that polymer crystal nucleation (i.e., the initial emergence of a nascent crystal) is phenomenologically distinct from crystal growth. These results highlight that the tailoring of polymeric materials requires strategies for controlling polymer crystal nucleation and growth at the nanoscale.

Polymer Nucleation under High-Driving Force, Long-Chain Conditions: Heat Release and the Separation of Timescales

2019 ◽  
Author(s):  
Kyle Hall ◽  
Simona Percec ◽  
Michael Klein
Keyword(s):  
Driving Force ◽  
Polymer Melts ◽  
Early Stage ◽  
Polymer Crystallization ◽  
Crystal Nucleation ◽  
Crystal Formation ◽  
Local Structures ◽  
Entangled Polymer ◽  
Entangled Polymer Melts ◽  
Chain Level

This study reveals important features of polymer crystal formation at high-driving forces in entangled polymer melts based on simulations of polyethylene. First and in contrast to small-molecule crystallization, the heat released during polymer crystallization does not appreciably influence structural details of early-stage, crystalline clusters (crystal nuclei). Second, early-stage polymer crystallization (crystal nucleation) can occur without substantial chain-level relaxation and conformational changes. This study's results indicate that local structures and environments guide crystal nucleation in entangled polymer melts under high-driving force conditions. Given that such conditions are often used to process polyethylene, local structures and the separation of timescales associated with crystallization and chain-level processes are anticipated to be of substantial importance to processing strategies. This study highlights new research directions for understanding polymer crystallization.

scholarly journals Simple, Accurate and User-Friendly Differential Constitutive Model for the Rheology of Entangled Polymer Melts and Solutions from Non-Equilibrium Thermodynamics

2020 ◽  
Author(s):  
Pavlos Stephanou ◽  
Ioanna Tsimouri ◽  
Vlasis Mavrantzas
Keyword(s):  
Large Scale ◽  
Polymer Melts ◽  
Second Law Of Thermodynamics ◽  
Equilibrium Thermodynamics ◽  
High Shear Rates ◽  
Entangled Polymer ◽  
Conformation Tensor ◽  
Entangled Polymer Melts ◽  
User Friendly ◽  
Non Equilibrium

In a recent reformulation of the Marrucci-Ianniruberto constitutive equation for the rheology of entangled polymer melts in the context of non-equilibrium thermodynamics, rather large values of the convective constraint release parameter \beta_{ccr} had to be used in order not to violate the second law of thermodynamics. In this work, we present an appropriate modification of the model which avoids the splitting of the evolution equation for the conformation tensor into an orientation and a stretching part. Then, thermodynamic admissibility dictates simply that \beta_{ccr}≥ 0, thus allowing for more realistic values of \beta_{ccr} to be chosen. Moreover, and in view of recent experimental evidence for a transient stress undershoot (following the overshoot) at high shear rates whose origin may be traced back to molecular tumbling, we have incorporated in the model additional terms accounting, at least in an approximate way, for non-affine deformation through a slip parameter \xi. Use of the new model to describe available experimental data for the transient and steady-state shear and elongational rheology of entangled polystyrene melts and solutions shows close agreement. Overall, the modified model proposed here combines simplicity with accuracy, which renders it an excellent choice for managing complex viscoelastic fluid flows in large-scale numerical calculations.

scholarly journals Simple, Accurate and User-Friendly Differential Constitutive Model for the Rheology of Entangled Polymer Melts and Solutions from Nonequilibrium Thermodynamics

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2867 ◽  
Author(s):  
Pavlos S. Stephanou ◽  
Ioanna Ch. Tsimouri ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Large Scale ◽  
Nonequilibrium Thermodynamics ◽  
Polymer Melts ◽  
Fluid Flows ◽  
Second Law Of Thermodynamics ◽  
High Shear Rates ◽  
Entangled Polymer ◽  
Conformation Tensor ◽  
Entangled Polymer Melts ◽  
User Friendly

In a recent reformulation of the Marrucci-Ianniruberto constitutive equation for the rheology of entangled polymer melts in the context of nonequilibrium thermodynamics, rather large values of the convective constraint release parameter βccr had to be used in order for the model not to violate the second law of thermodynamics. In this work, we present an appropriate modification of the model, which avoids the splitting of the evolution equation for the conformation tensor into an orientation and a stretching part. Then, thermodynamic admissibility simply dictates that βccr ≥ 0, thus allowing for more realistic values of βccr to be chosen. Moreover, and in view of recent experimental evidence for a transient stress undershoot (following the overshoot) at high shear rates, whose origin may be traced back to molecular tumbling, we have incorporated additional terms into the model accounting, at least in an approximate way, for non-affine deformation through a slip parameter ξ. Use of the new model to describe available experimental data for the transient and steady-state shear and elongational rheology of entangled polystyrene melts and concentrated solutions shows close agreement. Overall, the modified model proposed here combines simplicity with accuracy, which renders it an excellent choice for managing complex viscoelastic fluid flows in large-scale numerical calculations.

Polymer Nucleation under High-Driving Force, Long-Chain Conditions: Heat Release and the Separation of Timescales

2019 ◽  
Author(s):  
Kyle Hall ◽  
Simona Percec ◽  
Michael Klein
Keyword(s):  
Driving Force ◽  
Polymer Melts ◽  
Early Stage ◽  
Polymer Crystallization ◽  
Crystal Nucleation ◽  
Crystal Formation ◽  
Local Structures ◽  
Entangled Polymer ◽  
Entangled Polymer Melts ◽  
Chain Level

This study reveals important features of polymer crystal formation at high-driving forces in entangled polymer melts based on simulations of polyethylene. First and in contrast to small-molecule crystallization, the heat released during polymer crystallization does not appreciably influence structural details of early-stage, crystalline clusters (crystal nuclei). Second, early-stage polymer crystallization (crystal nucleation) can occur without substantial chain-level relaxation and conformational changes. This study's results indicate that local structures and environments guide crystal nucleation in entangled polymer melts under high-driving force conditions. Given that such conditions are often used to process polyethylene, local structures and the separation of timescales associated with crystallization and chain-level processes are anticipated to be of substantial importance to processing strategies. This study highlights new research directions for understanding polymer crystallization.

scholarly journals Environmental Assessment of Large Scale Production of Magnetite (Fe3O4) Nanoparticles via Coprecipitation

2019 ◽  
Vol 9 (8) ◽  
pp. 1682 ◽  
Author(s):  
Steffy J. Arteaga-Díaz ◽  
Samir I. Meramo-Hurtado ◽  
Jeffrey León-Pulido ◽  
Antonio Zuorro ◽  
Angel D. González-Delgado
Keyword(s):  
Environmental Assessment ◽  
Magnetite Nanoparticles ◽  
Large Scale ◽  
Polymeric Materials ◽  
Scale Production ◽  
Large Scale Production ◽  
Magnetite Fe3o4 ◽  
Key Characteristics ◽  
Important Challenge ◽  
Negative Impacts

Nanoparticles are materials with special properties that can be applied in different fields, such as medicine, engineering, food industry and cosmetics. The contributions regarding the synthesis of different types of nanoparticles have allowed researchers to determine a special group of nanoparticles with key characteristics for several applications. Magnetite nanoparticles (Fe3O4) have attracted a significant amount of attention due to their ability to improve the properties of polymeric materials. For this reason, the development of novel/emerging large scale processes for the synthesis of nanomaterials is a great and important challenge. In this work, an environmental assessment of the large scale production of magnetite via coprecipitation was carried out with the aim to evaluate its potential impact on the environment at a processing capacity of 806.87 t/year of magnetite nanoparticles. The assessment was performed using a computer-aided tool based on the Waste Reduction Algorithm (WAR). This method allows us to quantify the impacts generated and classify them into eight different categories. The process does not generate any negative impacts that could harm the environment. This assessment allowed us to identify the applicability of the large scale production of magnetite nanoparticles from an environmental viewpoint.

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