Article
Polymer Science
Seung Heum Jeong, Soowon Cho, Chunggi Baig
Summary: This study presents a detailed analysis of the scaling behavior of chain rotation dynamics in shear flow for melt and dilute linear polymer systems. The results show that dilute systems with hydrodynamic interaction (HI) and excluded volume (EV) effects exhibit two distinct scaling behaviors of chain rotation time between the intermediate and strong flow regimes. In contrast, free-draining dilute polymer systems display a simpler single-scaling behavior throughout the intermediate-to-strong flow regimes. The combined HI and EV effects weaken the structural change of polymer chains and enhance chain rotation dynamics by disturbing chain stretch and alignment to the flow direction. The presence of intermolecular interactions between chains in melt systems leads to two distinct scaling behaviors of chain rotation time as well. The overall scaling behavior of chain rotation is determined by the kinematically stable angular regions near the flow direction, while the kinematically unstable angular regions exhibit affine chain rotation dynamics. This study provides important insights into the understanding of chain rotation dynamics in shear flow.
Article
Mechanics
Mandi Boudaghi, M. Hadi Nafar Seddashti, Brian J. Edwards, Bamin Khomami
Summary: Dissipative particle dynamics (DPD) simulations replicate the coil-stretch transition (CST) and configurational relaxation of entangled polyethylene melts observed in planar elongational flow (PEF). The width of the CST hysteresis loop is larger for longer molecule liquids. Reducing the flow Deborah number results in a two-stage relaxation process, with initial stratification followed by configurational relaxation.
JOURNAL OF RHEOLOGY
(2022)
Article
Mechanics
Manfred H. Wagner, Esmaeil Narimissa, Qian Huang
Summary: The study extends the criterion for brittle fracture of entangled polymer liquids by considering the effects of finite chain extensibility and polymer concentration. Experimental data and models support the finding that crack initiation originates from the rupture of C-C bonds, leading to the fracture of polymer chains and crack propagation.
JOURNAL OF RHEOLOGY
(2021)
Review
Polymer Science
Daniele Parisi, Jiho Seo, Richard P. Schaake, Alicyn M. Rhoades, Ralph H. Colby
Summary: This study focuses on the shear-induced isotropic-nematic transition exhibited by PEEK melts, revealing a relationship between zero-shear viscosity and molecular weight. The shear-induced I-N transition is characterized by three distinct regimes in the flow curves, providing insights into this intriguing phenomenon.
PROGRESS IN POLYMER SCIENCE
(2021)
Article
Chemistry, Physical
Alexander Ya Malkin, Igor' Gumennyi, Ali D. Aliev, Anatoly E. Chalykh, Valery G. Kulichikhin
Summary: The study analyzed the evolution of the morphology of two incompatible polymer melts in a capillary flow using analytical electron microscopy. The spatial distribution and orientation of the polymers were found to be minimally affected by the specified shear rate, with a thin boundary layer formed by the low-viscosity LC polymer being the only significant change observed.
JOURNAL OF MOLECULAR LIQUIDS
(2021)
Article
Polymer Science
Daniele Parisi, Salvatore Costanzo, Youncheol Jeong, Junyoung Ahn, Taihyun Chang, Dimitris Vlassopoulos, Jonathan D. Halverson, Kurt Kremer, Ting Ge, Michael Rubinstein, Gary S. Grest, Watee Srinin, Alexander Y. Grosberg
Summary: Experimental, simulation, and theoretical studies on the steady-state shear viscosity of unconcatenated ring polymer melts show weaker shear thinning compared to linear polymers, with a power law relationship between shear viscosity and shear rate independent of chain length.
Article
Polymer Science
Wei Li, Pritam K. Jana, Alireza F. Behbahani, Georgios Kritikos, Ludwig Schneider, Patrycja Polinska, Craig Burkhart, Vagelis A. Harmandaris, Marcus Mueller, Manolis Doxastakis
Summary: A hierarchical triple-scale simulation methodology is applied to investigate the dynamics of cis-1,4 polyisoprene melts, showing good agreement with experimental data, especially for highly entangled polymer melts. The study provides parameter-free predictions on the dynamics of polymeric materials.
Article
Polymer Science
Yexin Zheng, Mesfin Tsige, Shi-Qing Wang
Summary: In this study, molecular dynamics simulations were used to investigate the entanglement lockup phenomena in the uniaxial melt stretching of entangled polymer melts. The results revealed that under high strains, the entanglement network became increasingly tighter, leading to chain tension and the formation of network junctions. It was hypothesized that the interchain entanglement at junctions can lockup as long as certain conditions are met. This study provides insights into the mechanical properties of polymer materials.
MACROMOLECULAR RAPID COMMUNICATIONS
(2023)
Review
Polymer Science
Yumi Matsumiya, Hiroshi Watanabe
Summary: The rheological behavior of polymeric liquids was traditionally believed to be universally determined by a few time-independent molecular parameters, but recent studies have shown non-universality under extensional flow conditions. A key concept is the reduction of segmental friction of highly oriented/stretched polymer chains, which changes with the chemical structure of the polymer and solvent as well as the polymer concentration.
PROGRESS IN POLYMER SCIENCE
(2021)
Article
Polymer Science
Heyi Liang, Kenji Yoshimoto, Masahiro Kitabata, Umi Yamamoto, Juan J. de Pablo
Summary: In this study, a multiscale simulation method is used to investigate the rheological properties of entangled Nylon 6 melts. The calculated results agree reasonably with experiments, showing the potential of this approach for designing polymeric materials based on purely molecular models.
JOURNAL OF POLYMER SCIENCE
(2022)
Article
Physics, Applied
Ji-Xuan Hou
Summary: In this paper, a coarse-graining method is presented to obtain the primitive chain from a polymer chain configuration in the entangled polymer melt by eliminating high-frequency Rouse modes. Theoretical demonstration shows that the tube step length is twice the tube diameter using this coarse-graining procedure. Additionally, a simple method to visualize the tube by adding high-frequency modes to the primitive chain is also provided.
MODERN PHYSICS LETTERS B
(2023)
Article
Chemistry, Physical
I. V. Brekotkin, N. F. Fatkullin, K. Lindt, C. Mattea, S. Stapf
Summary: This article introduces the spatial displacements of spins and their impact on the DQ Hamiltonian in a double-quantum nuclear magnetic resonance pulse sequence. It provides a simple expression for estimating and controlling the contributions to the initial rise of the DQ build-up function by varying experimental parameters. The application of polymers is also discussed.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Mahdi Boudaghi, Brian J. J. Edwards, Bamin Khomami
Summary: The evolution of shear banding under startup of shear flow was simulated for different molecular weight polyethylene melts. It was found that shear stress was dominated by segmental orientation at low shear rates, but flow-induced disentanglement resulted in the onset of chain tumbling and reduced shear stress at a critical shear rate. During shear flow startup, distinct fast and slow bands formed, consisting of more disentangled and extended chains and relatively entangled and coiled molecules, respectively. The simulation results showed temporary reverse flow, consistent with earlier experiments and theoretical results. The phenomenon of shear banding appeared to arise from flow-induced disentanglement and differential stretching of individual chains, resulting in the formation of slow and fast bands.
Article
Polymer Science
Heyi Liang, Kenji Yoshimoto, Phwey Gil, Masahiro Kitabata, Umi Yamamoto, Juan J. de Pablo
Summary: A multiscale computational method is proposed for predicting the viscoelastic properties of entangled homopolymer melts with high glass transition temperatures. The method combines atomistic, coarse-grained, and slip-spring representations to achieve accurate predictions of the melt's linear rheology.
Article
Chemistry, Physical
Kanjana Sirirak, Visit Vao-soongnern
Summary: The stiffness of polymer chains is closely related to the macroscopic properties of polymeric materials. This study aims to investigate the role of chain stiffness in controlling polymer crystallization. Molecular simulations show that the rate of structural formation and the degree of crystallinity are influenced by the chain stiffness parameter.
JOURNAL OF MOLECULAR LIQUIDS
(2023)
Article
Chemistry, Physical
Mohammad Hadi Nafar Sefiddashti, Brian J. Edwards, Bamin Khomami, Eric S. G. Shaqfeh
Summary: Recent NEMD simulations have shown that extensional flow of entangled polymer melts can lead to the coexistence of separate domains consisting primarily of either coiled or stretched chain-like macromolecules. This flow-induced phase separation results in bimodal configurational distributions, which are only possible when the CCR parameters are consistent with the rate of flow-induced disentanglement.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Chemistry, Physical
Brian J. Edwards, M. Hadi Nafar Sefiddashti, Bamin Khomami
Summary: The quantification of configurational entropy in polymeric liquids presents a challenge in nonequilibrium thermodynamics. Theoretical calculations based on three-dimensional probability distributions can provide insight into entropy values but require significant computational resources and face challenges in relating atomic positions to configurational mesostates.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Mechanics
Jiaxing Song, Fenghui Lin, Nansheng Liu, Xi-Yun Lu, Bamin Khomami
Summary: The flow physics of inertio-elastic turbulent Taylor-Couette flow with a radius ratio of 0.5 in the Reynolds number range of 500 to 8000 was investigated through direct numerical simulation. The study revealed two distinct regimes of turbulence dynamics as Reynolds number increases, with either nonlinear elastic forces or inertial forces dominating the flow physics in the low and high Reynolds number regimes, impacting the flow structures in the bulk and near-wall regions differently. Examination of the flow-microstructure coupling analysis showed the triggering of elastic Gortler instability in the near-wall region, leading to the formation of small-scale elastic vortical structures known as elastic Gortler vortices with longer average life span compared to their Newtonian counterparts.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jiaxing Song, Zhen-Hua Wan, Nansheng Liu, Xi-Yun Lu, Bamin Khomami
Summary: A high-order transition route has been discovered in Taylor-Couette flows of polymeric solutions, transitioning from inertial to elasticity-dominated turbulence via direct numerical simulations. This two-step transition route involves stabilizing inertial turbulence to laminar flow resembling modulated wavy vortex flow, then destabilizing the laminar flow state to elasticity-dominated turbulence. This transition is achieved by enhancing the extensional viscosity and hoop stresses of the polymeric solution.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Multidisciplinary
Brian Joseph Edwards, Mohammad Hadi Nafar Sefiddashti, Bamin Khomami
Summary: This study tackles the challenge of calculating nonequilibrium entropy in polymeric liquids undergoing flow by extending equilibrium thermodynamics and applying it to nonequilibrium conditions. By introducing internal variables that quantify the internal microstructure of chain-like macromolecules and assuming an evolution of quasi-equilibrium states, the authors were able to determine the nonequilibrium entropy at different levels of coarse-graining.
Article
Mechanics
Brian J. Edwards, M. Hadi Nafar Sefiddashti, Bamin Khomami
Summary: This retrospective covers the growth and application of atomistic simulations of alkanes and polyethylenes over a 50-year period, focusing on the development of accurate potential models and the application of molecular dynamics methodology. The authors summarize the results of simulations from the past 50 years, providing a coherent history of the subject and highlighting the significant impacts on the field of polymer rheology.
JOURNAL OF RHEOLOGY
(2022)
Article
Mechanics
Mandi Boudaghi, M. Hadi Nafar Seddashti, Brian J. Edwards, Bamin Khomami
Summary: Dissipative particle dynamics (DPD) simulations replicate the coil-stretch transition (CST) and configurational relaxation of entangled polyethylene melts observed in planar elongational flow (PEF). The width of the CST hysteresis loop is larger for longer molecule liquids. Reducing the flow Deborah number results in a two-stage relaxation process, with initial stratification followed by configurational relaxation.
JOURNAL OF RHEOLOGY
(2022)
Article
Mechanics
Jiaxing Song, Nansheng Liu, Xi-Yun Lu, Bamin Khomami
Summary: Three-dimensional elastic turbulence in Taylor-Couette flows of dilute polymer solutions has been achieved and studied through direct numerical simulations. A novel flow transition pathway from elastically dominated turbulence to solitary vortex pairs and eventually to purely elastic turbulence is observed by decreasing fluid inertia. The dominant flow features in the elastic turbulence regime are large-scale unsteady vortex pairs and small-scale traveling waves. Furthermore, the study concludes that the production of turbulent kinetic energy in purely elastic turbulence is solely due to the stochastic nature of polymer stretch/relaxation.
JOURNAL OF FLUID MECHANICS
(2022)
Review
Multidisciplinary Sciences
Jiaxing Song, Yabiao Zhu, Fenghui Lin, Nansheng Liu, Bamin Khomami
Summary: This retrospective aims to present a coherent history of important findings in direct numerical simulations and experiments in turbulent Taylor-Couette flow of dilute polymeric solutions in the last decade. Specifically, the article discusses the sequence of flow transitions due to an increase in fluid elasticity, including drag modification, flow structures, statistics, and mechanisms of turbulence, as well as a comparison with curvilinear and rectilinear shear flows. This article is part of a theme issue on Taylor-Couette and related flows.
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2023)
Article
Chemistry, Physical
Mahdi Boudaghi, Brian J. J. Edwards, Bamin Khomami
Summary: The evolution of shear banding under startup of shear flow was simulated for different molecular weight polyethylene melts. It was found that shear stress was dominated by segmental orientation at low shear rates, but flow-induced disentanglement resulted in the onset of chain tumbling and reduced shear stress at a critical shear rate. During shear flow startup, distinct fast and slow bands formed, consisting of more disentangled and extended chains and relatively entangled and coiled molecules, respectively. The simulation results showed temporary reverse flow, consistent with earlier experiments and theoretical results. The phenomenon of shear banding appeared to arise from flow-induced disentanglement and differential stretching of individual chains, resulting in the formation of slow and fast bands.
Article
Physics, Fluids & Plasmas
Jiaxing Song, Fenghui Lin, Yabiao Zhu, Zhen-Hua Wan, Nansheng Liu, Xi-Yun Lu, Bamin Khomami
Summary: Direct numerical simulation is used to identify the dominant flow structures in the Taylor-Couette flow of dilute polymer solutions. It is found that unsteady diwhirls and elastic waves play important roles in the formation of elastic turbulence. The interaction between these elements leads to stochastic or chaotic cycles that sustain the turbulent dynamics.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Mechanics
Yabiao Zhu, Zhenhua Wan, Fenghui Lin, Nansheng Liu, Xiyun Lu, Bamin Khomami
Summary: The existence of a maximum drag enhancement (MDE) asymptote at high rotation (Ro) and Weissenberg (Wi) numbers in turbulent viscoelastic spanwise-rotating plane Couette flow has been demonstrated. Above a critical Wi, drag enhancement plateaus and the MDE asymptote is realized in a broad range of Ro. The mean velocity profiles at MDE closely follow a log-law profile that has a nearly identical slope but different intercepts as a function of Ro. Moreover, the intriguing finding is that MDE occurs in the elasto-inertial turbulence (EIT) flow state and is mainly sustained by elastic forces like the MDR flow state. Hence, a universal picture of elastically induced drag modification asymptotes is emerging, where these asymptotic states are inherent to the elastically sustained EIT flow state.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Polymer Science
Mohammad Hadi Nafar Sefiddashti, Brian J. Edwards, Bamin Khomami
Summary: Atomistic simulations were performed on linear, entangled polyethylene melt under uniaxial elongational flow conditions. Flow-induced phase separation and crystallization were observed at intermediate and high flow strengths, respectively. The flow-induced crystallization occurred at a temperature higher than the quiescent melting point and remained stable after flow cessation. The results were consistent with experimental measurements of thermodynamic properties.
Article
Chemistry, Multidisciplinary
Mahshid Mokhtarnejad, Erick L. Ribeiro, Dibyendu Mukherjee, Bamin Khomami
Summary: In this study, hybrid nanocomposites (HNCs) based on manganese oxides (MnOx/Mn3O4) and reduced graphene oxide (rGO) were synthesized as active electrodes for energy storage devices. The active material was composed of MnOx/Mn3O4 nanorods and nanoparticles embedded in rGO nanosheets. The performance of the active layer was highly correlated with the MnOx/Mn3O4 to rGO ratio and the morphology of MnOx/Mn3O4 nanostructures in HNCs. Electrochemical characterizations showed that the MnOx/Mn3O4-rGO composite exhibited significantly higher specific capacitance compared to commercially available Mn3O4-graphene nanocomposites. The study has paved the way for the use of LASiS-based synthesized functional material in combination with additive manufacturing techniques for all-printed electronics with superior performance.
Article
Chemistry, Physical
Erick L. Ribeiro, Elijah M. Davis, Mahshid Mokhtarnejad, Sheng Hu, Dibyendu Mukherjee, Bamin Khomami
Summary: This study presents a facile technique for synthesizing Pt-Co bimetallic nanoparticles with superior electrocatalytic activities for oxygen reduction reaction. By adjusting the precursor concentrations, a higher degree of Pt-Co alloying can be facilitated to enhance catalytic activities while maintaining long-term stabilities in highly concentrated alkaline media. The unique configurations of the Pt-Co nanoparticles coated with a graphitic shell and supported by Co3O4-decorated carbon matrix contribute to the outstanding performances.
CATALYSIS SCIENCE & TECHNOLOGY
(2021)