Nonequilibrium Thermodynamics of Polymeric Liquids via Atomistic Simulation

Edwards, Brian J.; Sefiddashti, Mohammad Hadi Nafar; Khomami, Bamin

doi:10.3390/e24020175

Cited by 3 publications

(1 citation statement)

References 51 publications

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“…Second, a one-to-one comparison of these results with those obtained for the same PE melt undergoing PEF will be made over the same range of extension rates. The majority of the PEF simulation results presented below were taken from a series of papers of prior work on this subject [7,8,17,18,54].…”

Section: Introductionmentioning

confidence: 99%

Atomistic Simulation of Flow-Induced Microphase Separation and Crystallization of an Entangled Polyethylene Melt Undergoing Uniaxial Elongational Flow and the Role of Kuhn Segment Extension

2023

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Atomistic simulations of the linear, entangled polyethylene C1000H2002 melt undergoing steady-state and startup conditions of uniaxial elongational flow (UEF) over a wide range of flow strength were performed using a united-atom model for the atomic interactions between the methylene groups constituting the polymer macromolecules. Rheological, topological, and microstructural properties of these nonequilibrium viscoelastic materials were computed as functions of strain rate, focusing on regions of flow strength where flow-induced phase separation and flow-induced crystallization were evident. Results of the UEF simulations were compared with those of prior simulations of planar elongational flow, which revealed that uniaxial and planar flows exhibited essentially a universal behavior, although over strain rate ranges that were not completely equivalent. At intermediate flow strength, a purely configurational microphase separation was evident that manifested as a bicontinuous phase composed of regions of highly stretched molecules that enmeshed spheroidal domains of relatively coiled chains. At high flow strength, a flow-induced crystallization (FIC) occurred, producing a semicrystalline material possessing a high degree of crystallinity and primarily a monoclinic lattice structure. This FIC phase formed at a temperature (450 K) high above the quiescent melting point (≈400 K) and remained stable after cessation of flow for temperature at or below 435 K. Careful examination of the Kuhn segments constituting the polymer chains revealed that the FIC phase only formed once the Kuhn segments had become essentially fully extended under the UEF flow field. Thermodynamic properties such as the heat of fusion and heat capacity were estimated from the simulations and found to compare favorably with experimental values.

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Section: Introductionmentioning

confidence: 99%

Atomistic Simulation of Flow-Induced Microphase Separation and Crystallization of an Entangled Polyethylene Melt Undergoing Uniaxial Elongational Flow and the Role of Kuhn Segment Extension

2023

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Flow-induced phase phenomena in an entangled polyethylene/benzene solution under uniaxial elongational flow

Nafar Sefiddashti,

Edwards,

Khomami

2023

Rheol Acta

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Comparative analysis of fluctuations in viscoelastic stress: A comparison of the temporary network and dumbbell models

Winters,

Öttinger,

Vermant

2024

The Journal of Chemical Physics

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Traditionally, stress fluctuations in flowing and deformed materials are overlooked, with an obvious focus on average stresses in a continuum mechanical approximation. However, these fluctuations, often dismissed as “noise,” hold the potential to provide direct insights into the material structure and its structure-stress coupling, uncovering detailed aspects of fluid transport and relaxation behaviors. Despite advancements in experimental techniques allowing for the visualization of these fluctuations, their significance remains largely untapped as modeling efforts continue to target Newtonian fluids within the confines of Gaussian noise assumptions. In the present work, a comparative analysis of stress fluctuations in two distinct microstructural models is carried out: the temporary network model and the hydrodynamic dumbbell model. Despite both models conforming to the upper convected Maxwell model at a macroscopic level, the temporary network model predicts non-Gaussian fluctuations. We find that stress fluctuations within the temporary network model exhibit more pronounced abruptness at the local scale, with only an enlargement of the control volume leading to a gradual Gaussian-like noise, diminishing the differences between the two models. These findings underscore the heightened sensitivity of fluctuating rheology to microstructural details and the microstructure–flow coupling, beyond what is captured by macroscopically averaged stresses.

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Nonequilibrium Thermodynamics of Polymeric Liquids via Atomistic Simulation

Cited by 3 publications

References 51 publications

Atomistic Simulation of Flow-Induced Microphase Separation and Crystallization of an Entangled Polyethylene Melt Undergoing Uniaxial Elongational Flow and the Role of Kuhn Segment Extension

Atomistic Simulation of Flow-Induced Microphase Separation and Crystallization of an Entangled Polyethylene Melt Undergoing Uniaxial Elongational Flow and the Role of Kuhn Segment Extension

Flow-induced phase phenomena in an entangled polyethylene/benzene solution under uniaxial elongational flow

Comparative analysis of fluctuations in viscoelastic stress: A comparison of the temporary network and dumbbell models

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