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Full-Text Articles in Engineering
Dynamics Of Individual Molecules Of Linear Polyethylene Liquids Under Shear: Atomistic Simulation And Comparison With A Free-Draining Bead-Rod Chain, J. M. Kim, B. J. Edwards, David J. Keffer, B. Khomami
Dynamics Of Individual Molecules Of Linear Polyethylene Liquids Under Shear: Atomistic Simulation And Comparison With A Free-Draining Bead-Rod Chain, J. M. Kim, B. J. Edwards, David J. Keffer, B. Khomami
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
Nonequilibrium molecular dynamics (NEMD) simulations of a dense liquid composed of linear polyethylene chains were performed to investigate the chain dynamics under shear. Brownian dynamics (BD) simulations of a freely jointed chain with equivalent contour length were also performed in the case of a dilute solution. This allowed for a close comparison of the chain dynamics of similar molecules for two very different types of liquids. Both simulations exhibited a distribution of the end-to-end vector, |Rete|, with Gaussian behavior at low Weissenberg number (Wi). At high Wi, the NEMD distribution was bimodal, with two peaks …
Rheological And Structural Studies Of Linear Polyethylene Melts Under Planar Elongational Flow Using Nonequilibrium Molecular Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran, V. A. Harmandaris
Rheological And Structural Studies Of Linear Polyethylene Melts Under Planar Elongational Flow Using Nonequilibrium Molecular Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran, V. A. Harmandaris
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
We present various rheological and structural properties of three polyethylene liquids, C50H102, C78H158, and C128H258, using nonequilibrium molecular dynamics simulations of planar elongational flow. All three melts display tension-thinning behavior of both elongational viscosities, η1 and η2. This tension thinning appears to follow the power law with respect to the elongation rate, i.e., η ∼ Eb, where the exponent b is shown to be approximately −0.4 for η1 and η2. More specifically, b of η1 is shown to be …
A Validation Of The P-Sllod Equations Of Motion For Homogeneous Steady-State Flows, David J. Keffer, B. J. Edwards, C. Baig
A Validation Of The P-Sllod Equations Of Motion For Homogeneous Steady-State Flows, David J. Keffer, B. J. Edwards, C. Baig
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
A validation of the p-SLLOD equations of motion for nonequilibrium molecular dynamics simulation under homogeneous steady-state flow is presented. We demonstrate that these equations generate the correct center-of-mass trajectory of the system, are completely compatible with (and derivable from) Hamiltonian dynamics, satisfy an appropriate energy balance, and require no fictitious external force to generate the required homogeneous flow. It is also shown that no rigorous derivation of the SLLOD equations exists to date.
A Comparison Of Simple Rheological Models And Simulation Data Of N-Hexadecane Under Shear And Elongational Flows, David J. Keffer, C. Baig, B. Jiang, B. J. Edwards, H. D. Cochran
A Comparison Of Simple Rheological Models And Simulation Data Of N-Hexadecane Under Shear And Elongational Flows, David J. Keffer, C. Baig, B. Jiang, B. J. Edwards, H. D. Cochran
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
The microscopic origins of five rheological models are investigated by comparing their predictions for the conformation tensor and stress tensor with the same tensors obtained via nonequilibrium molecular dynamics simulations for n-hexadecane. Steady-state simulations were performed under both planar Couette and planar elongational flows, and the results of each are compared with rheological model predictions in the same flows, without any fitting parameters where possible. The use of the conformation tensor for comparisons between theory and experiment/simulation, rather than just the stress tensor, allows additional information to be obtained regarding the physical basis of each model examined herein. The character …
An Examination Of The Validity Of Nonequilibrium Molecular-Dynamics Simulation Algorithms For Arbitrary Steady-State Flows, David J. Keffer, Brian J. Edwards, Chunggi Baig
An Examination Of The Validity Of Nonequilibrium Molecular-Dynamics Simulation Algorithms For Arbitrary Steady-State Flows, David J. Keffer, Brian J. Edwards, Chunggi Baig
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
Nonlinear-response theory of nonequilibrium molecular-dynamics simulation algorithms is considered under the imposition of an arbitrary steady-state flow field. It is demonstrated that the SLLOD and DOLLS algorithms cannot be used for general flows, although the SLLOD algorithm is rigorous for planar Couette flow. Following the same procedure used to establish SLLOD as the valid algorithm for planar Couette flow [ D. J. Evans and E. P. Morriss, Phys. Rev. A 30, 1528 (1984) ], it is demonstrated that the p-SLLOD algorithm is valid for arbitrary flows and produces the correct nonlinear response of the viscous pressure tensor.
Rheological And Structural Studies Of Liquid Decane, Hexadecane, And Tetracosane Under Planar Elongational Flow Using Nonequilibrium Molecular-Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran
Rheological And Structural Studies Of Liquid Decane, Hexadecane, And Tetracosane Under Planar Elongational Flow Using Nonequilibrium Molecular-Dynamics Simulations, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
We report for the first time rheological and structural properties of liquid decane, hexadecane, and tetracosane using nonequilibrium molecular-dynamics (NEMD) simulations under planar elongational flow (PEF). The underlying NEMD algorithm employed is the so-called p-SLLOD algorithm [ C. Baig, B. J. Edwards, D. J. Keffer, and H. D. Cochran, J. Chem. Phys. 122, 114103 (2005) ]. Two elongational viscosities are measured, and they are shown not to be equal to each other, indicating two independent viscometric functions in PEF. With an appropriate definition, it is observed that the two elongational viscosities converge to each other at very low elongation …
A Proper Approach For Nonequilibrium Molecular Dynamics Simulations Of Planar Elongational Flow, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran
A Proper Approach For Nonequilibrium Molecular Dynamics Simulations Of Planar Elongational Flow, David J. Keffer, C. Baig, B. J. Edwards, H. D. Cochran
Faculty Publications and Other Works -- Chemical and Biomolecular Engineering
We present nonequilibrium molecular dynamics simulations of planar elongational flow (PEF) by an algorithm proposed by Tuckerman et al. [J. Chem. Phys. 106, 5615 (1997)] and theoretically elaborated by Edwards and Dressler [J. Non-Newtonian, Fluid Mech. 96, 163 (2001)], which we shall call the proper-SLLOD algorithm, or p-SLLOD for short. [For background on names of algorithms see W. G. Hoover, D. J. Evans, R. B. Hickman, A. J. C. Ladd, W. T. Ashurst, and B. Moran, Phys. Rev. A 22, 1690 (1980) and D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984).] We show that there …