1
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Stanković I, Dašić M, Jovanović M, Martini A. Effects of Water Content on the Transport and Thermodynamic Properties of Phosphonium Ionic Liquids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:9049-9058. [PMID: 38641549 DOI: 10.1021/acs.langmuir.4c00372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/21/2024]
Abstract
We present a numerical investigation of the influence of water content on the dynamic properties of a family of phosphonium-based room-temperature ionic liquids. The study presents a compelling correlation between structural changes in water-ionic liquid solutions and thermodynamic and transport properties across diverse systems. The results for phosphonium ionic liquids are compared with 1-butyl-3-methylimidazolium hexaphosphate ([bmim]PF6) as a reference. Through this approach, phosphonium cation structure-related characteristics can be identified and placed within the broader context of ionic liquids. These insights are underpinned by observed changes in interaction energy, boiling point, diffusion rate, and viscosity, highlighting the crucial role of water molecules in weakening the strength of interactions between ions within the ionic liquid. The investigation also explains temperature-dependent trends in phosphonium cations, showing that alkyl group length and molecular symmetry are important tuning parameters for the strength of Coulomb interactions. These results contribute to a refined understanding of phosphonium ionic liquid behavior in the presence of water, offering valuable insights for optimizing their use in diverse fields.
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Affiliation(s)
- Igor Stanković
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Miljan Dašić
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Mateja Jovanović
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Ashlie Martini
- Department of Mechanical Engineering, University of California, Merced, California 95343, United States
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2
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Moussavi A, Pal S, Wu Z, Keten S. Characterizing the shear response of polymer-grafted nanoparticles. J Chem Phys 2024; 160:134903. [PMID: 38573850 DOI: 10.1063/5.0188494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 03/18/2024] [Indexed: 04/06/2024] Open
Abstract
Grafting polymer chains to the surface of nanoparticles overcomes the challenge of nanoparticle dispersion within nanocomposites and establishes high-volume fractions that are found to enable enhanced material mechanical properties. This study utilizes coarse-grained molecular dynamics simulations to quantify how the shear modulus of polymer-grafted nanoparticle (PGN) systems in their glassy state depends on parameters such as strain rate, nanoparticle size, grafting density, and chain length. The results are interpreted through further analysis of the dynamics of chain conformations and volume fraction arguments. The volume fraction of nanoparticles is found to be the most influential variable in deciding the shear modulus of PGN systems. A simple rule of mixture is utilized to express the monotonic dependence of shear modulus on the volume fraction of nanoparticles. Due to the reinforcing effect of nanoparticles, shortening the grafted chains results in a higher shear modulus in PGNs, which is not seen in linear systems. These results offer timely insight into calibrating molecular design parameters for achieving the desired mechanical properties in PGNs.
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Affiliation(s)
- Arman Moussavi
- Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Subhadeep Pal
- Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Zhenghao Wu
- Department of Chemistry, Xi'an Jiaotong Liverpool University, Suzhou, People's Republic of China
| | - Sinan Keten
- Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, USA
- Department of Mechanical Engineering, Northwestern University, Evanston, Illinois 60208, USA
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3
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Singh P, Ranganathan R. Mechanical and Viscoelastic Properties of Stacked and Grafted Graphene/Graphene Oxide-Polyethylene Nanocomposites: A Coarse-Grained Molecular Dynamics Study. ACS OMEGA 2024; 9:9063-9075. [PMID: 38434848 PMCID: PMC10906040 DOI: 10.1021/acsomega.3c07690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 01/30/2024] [Accepted: 02/06/2024] [Indexed: 03/05/2024]
Abstract
High-performance natural materials with superior mechanical properties often possess a hierarchical structure across multiple length scales. Nacre, also known as the mother of pearl, is an example of such a material and exhibits remarkable strength and toughness. The layered hierarchical architecture across different length scales is responsible for the efficient toughness and energy dissipation. To develop high-performance artificial nacre-like composites, it is necessary to mimic this layered structure and understand the molecular phenomena at the interface. This study uses coarse-grained molecular dynamics simulations to investigate the structure-property relationship of stacked graphene-polyethylene (PE) nanocomposites. Uniaxial and oscillatory shear deformation simulations were conducted to explore the composites' mechanical and viscoelastic behavior. The effect of grafting on the glass-transition temperature and the mechanical and viscoelastic behavior was also examined. The two examined microstructures, the stacked and grafted GnP (graphene nanoplatelet)-PE composites, demonstrated significant enhancement in the Young's modulus and yield strength when compared to the pristine PE. The study also delves into the viscoelastic properties of polyethylene nanocomposites containing graphene and graphene oxide. The grafted composite demonstrated an increased elastic energy and improved capacity for stress transfer. Our study sheds light on the energy dissipation properties of layered nanocomposites through underlying molecular mechanisms, providing promising prospects for designing novel biomimetic polymer nanocomposites.
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Affiliation(s)
- Param
Punj Singh
- Department of Materials Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar 382355, India
| | - Raghavan Ranganathan
- Department of Materials Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar 382355, India
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4
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Lin X, Rondoni L, Zhao H. Fluctuation Relation for the Dissipative Flux: The Role of Dynamics, Correlations and Heat Baths. ENTROPY (BASEL, SWITZERLAND) 2024; 26:156. [PMID: 38392411 PMCID: PMC10887572 DOI: 10.3390/e26020156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 01/23/2024] [Accepted: 02/05/2024] [Indexed: 02/24/2024]
Abstract
The fluctuation relation stands as a fundamental result in nonequilibrium statistical physics. Its derivation, particularly in the stationary state, places stringent conditions on the physical systems of interest. On the other hand, numerical analyses usually do not directly reveal any specific connection with such physical properties. This study proposes an investigation of such a connection with the fundamental ingredients of the derivation of the fluctuation relation for the dissipation, which includes the decay of correlations, in the case of heat transport in one-dimensional systems. The role of the heat baths in connection with the system's inherent properties is then highlighted. A crucial discovery of our research is that different lattice models obeying the steady-state fluctuation relation may do so through fundamentally different mechanisms, characterizing their intrinsic nature. Systems with normal heat conduction, such as the lattice ϕ4 model, comply with the theorem after surpassing a certain observational time window, irrespective of lattice size. In contrast, systems characterized by anomalous heat conduction, such as Fermi-Pasta-Ulam-Tsingou-β and harmonic oscillator chains, require extended observation periods for theoretical alignment, particularly as the lattice size increases. In these systems, the heat bath's fluctuations significantly influence the entire lattice, linking the system's fluctuations with those of the bath. Here, the current autocorrelation function allows us to discern the varying conditions under which different systems satisfy with the fluctuation relation. Our findings significantly expand the understanding of the stationary fluctuation relation and its broader implications in the field of nonequilibrium phenomena.
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Affiliation(s)
- Xubin Lin
- Department of Physics, Xiamen University, Xiamen 361005, China
| | - Lamberto Rondoni
- Department of Mathematical Sciences, Politecnico di Torino, 10129 Turin, Italy
- Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Torino, 10125 Turin, Italy
| | - Hong Zhao
- Department of Physics, Xiamen University, Xiamen 361005, China
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5
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Mohottalalage SS, Saab AP, Maiti A. Bead-Spring Simulation of Ionomer Melts-Studying the Effects of Chain-Length and Associating Group Fraction on Equilibrium Structure and Extensional Flow Behavior. Polymers (Basel) 2023; 15:4560. [PMID: 38232005 PMCID: PMC10708384 DOI: 10.3390/polym15234560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 11/22/2023] [Accepted: 11/24/2023] [Indexed: 01/19/2024] Open
Abstract
Ionomers are associative polymers with diverse applications ranging from selective membranes and high-performance adhesives to abrasion- and chemical-resistant coatings, insulation layers, vacuum packaging, and foamed sheets. Within equilibrium melt, the ionic or associating groups are known to form thermally reversible, associative clusters whose presence can significantly affect the system's mechanical, viscoelastic, and transport properties. It is, thus, of great interest to understand how to control such clusters' size distribution, shape, and stability through the designed choice of polymer architecture and the ionic groups' fraction, arrangement, and interaction strength. In this work, we represent linear associating polymers using a Kremer-Grest type bead-spring model and perform large-scale MD simulations to explore the effect of polymer chain-length (l) and fraction (fs) of randomly placed associating groups on the size distribution and stability of formed clusters. We consider different chain-lengths (below and above entanglement), varying fractions of associating groups (represented by 'sticky' beads) between 5 and 20%, and a fixed sticky-sticky nonbond interaction strength of four times that between regular non-associating beads. For all melts containing associating groups the equilibrium structure factor S(q) displays a signature ionomer peak at low wave vector q whose intensity increases with increasing fs and l. The average cluster size Nc increases with fs. However, the effect of chain-length on Nc appears to be pronounced only at higher values of fs. Under extensional flows, the computed stress (and viscosity) is higher at higher fs and l regardless of strain rate. Beyond a critical strain rate, we observe fragmentation of the associative clusters, which has interesting effects on the stress/viscous response.
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Affiliation(s)
| | | | - Amitesh Maiti
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA; (S.S.M.)
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6
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Li W, Kadupitiya J, Jadhao V. Rheological Properties of Small-Molecular Liquids at High Shear Strain Rates. Polymers (Basel) 2023; 15:polym15092166. [PMID: 37177312 PMCID: PMC10180873 DOI: 10.3390/polym15092166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 04/26/2023] [Accepted: 04/27/2023] [Indexed: 05/15/2023] Open
Abstract
Molecular-scale understanding of rheological properties of small-molecular liquids and polymers is critical to optimizing their performance in practical applications such as lubrication and hydraulic fracking. We combine nonequilibrium molecular dynamics simulations with two unsupervised machine learning methods: principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE), to extract the correlation between the rheological properties and molecular structure of squalane sheared at high strain rates (106-1010s-1) for which substantial shear thinning is observed under pressures P∈0.1-955 MPa at 293 K. Intramolecular atom pair orientation tensors of 435×6 dimensions and the intermolecular atom pair orientation tensors of 61×6 dimensions are reduced and visualized using PCA and t-SNE to assess the changes in the orientation order during the shear thinning of squalane. Dimension reduction of intramolecular orientation tensors at low pressures P=0.1,100 MPa reveals a strong correlation between changes in strain rate and the orientation of the side-backbone atom pairs, end-backbone atom pairs, short backbone-backbone atom pairs, and long backbone-backbone atom pairs associated with a squalane molecule. At high pressures P≥400 MPa, the orientation tensors are better classified by these different pair types rather than strain rate, signaling an overall limited evolution of intramolecular orientation with changes in strain rate. Dimension reduction also finds no clear evidence of the link between shear thinning at high pressures and changes in the intermolecular orientation. The alignment of squalane molecules is found to be saturated over the entire range of rates during which squalane exhibits substantial shear thinning at high pressures.
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Affiliation(s)
- Wenhui Li
- Intelligent Systems Engineering, Indiana University, Bloomington, IN 47408, USA
| | - Jcs Kadupitiya
- Intelligent Systems Engineering, Indiana University, Bloomington, IN 47408, USA
| | - Vikram Jadhao
- Intelligent Systems Engineering, Indiana University, Bloomington, IN 47408, USA
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7
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Shi K, Smith ER, Santiso EE, Gubbins KE. A perspective on the microscopic pressure (stress) tensor: History, current understanding, and future challenges. J Chem Phys 2023; 158:040901. [PMID: 36725519 DOI: 10.1063/5.0132487] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The pressure tensor (equivalent to the negative stress tensor) at both microscopic and macroscopic levels is fundamental to many aspects of engineering and science, including fluid dynamics, solid mechanics, biophysics, and thermodynamics. In this Perspective, we review methods to calculate the microscopic pressure tensor. Connections between different pressure forms for equilibrium and nonequilibrium systems are established. We also point out several challenges in the field, including the historical controversies over the definition of the microscopic pressure tensor; the difficulties with many-body and long-range potentials; the insufficiency of software and computational tools; and the lack of experimental routes to probe the pressure tensor at the nanoscale. Possible future directions are suggested.
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Affiliation(s)
- Kaihang Shi
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
| | - Edward R Smith
- Department of Mechanical and Aerospace Engineering, Brunel University London, Uxbridge, London, United Kingdom
| | - Erik E Santiso
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
| | - Keith E Gubbins
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
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8
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Singh PP, Ranganathan R. Tensile and Viscoelastic Behavior in Nacre-Inspired Nanocomposites: A Coarse-Grained Molecular Dynamics Study. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:3333. [PMID: 36234462 PMCID: PMC9565923 DOI: 10.3390/nano12193333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Revised: 09/04/2022] [Accepted: 09/16/2022] [Indexed: 06/16/2023]
Abstract
Organisms hold an extraordinarily evolutionary advantage in forming complex, hierarchical structures across different length scales that exhibit superior mechanical properties. Mimicking these structures for synthesizing high-performance materials has long held a fascination and has seen rapid growth in the recent past thanks to high-resolution microscopy, design, synthesis, and testing methodologies. Among the class of natural materials, nacre, found in mollusk shells, exhibits remarkably high mechanical strength and toughness. The highly organized "brick and mortar" structure at different length scales is a basis for excellent mechanical properties and the capability to dissipate energy and propagation in nacre. Here, we employ large-scale atomistic coarse-grained molecular dynamics simulations to study the mechanical and viscoelastic behavior of nacre-like microstructures. Uniaxial tension and oscillatory shear simulations were performed to gain insight into the role of complex structure-property relationships. Specifically, the role played by the effect of microstructure (arrangement of the crystalline domain) and polymer-crystal interactions on the mechanical and viscoelastic behavior is elucidated. The tensile property of the nanocomposite was seen to be sensitive to the microstructure, with a staggered arrangement of the crystalline tablets giving rise to a 20-30% higher modulus and lower tensile strength compared to a columnar arrangement. Importantly, the staggered microstructure is shown to have a highly tunable mechanical behavior with respect to the polymer-crystal interactions. The underlying reasons for the mechanical behavior are explained by showing the effect of polymer chain mobility and orientation and the load-carrying capacity for the constituents. Viscoelastic responses in terms of the storage and loss moduli and loss tangent are studied over three decades in frequency and again highlight the differences brought about by the microstructure. We show that our coarse-grained models offer promising insights into the design of novel biomimetic structures for structural applications.
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9
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Perego A, Lazarenko D, Cloitre M, Khabaz F. Microscopic Dynamics and Viscoelasticity of Vitrimers. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Alessandro Perego
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, Ohio 44325, United States
| | - Daria Lazarenko
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, Ohio 44325, United States
| | - Michel Cloitre
- Molecular, Macromolecular Chemistry, and Materials, ESPCI Paris, CNRS, PSL Research University, 75005 Paris, France
| | - Fardin Khabaz
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, Ohio 44325, United States
- Department of Chemical, Biomolecular, and Corrosion Engineering, The University of Akron, Akron, Ohio 44325, United States
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10
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Monteferrante M, Tiribocchi A, Succi S, Pisignano D, Lauricella M. Capturing Free-Radical Polymerization by Synergetic Ab Initio Calculations and Topological Reactive Molecular Dynamics. Macromolecules 2022; 55:1474-1486. [PMID: 35287293 PMCID: PMC8909409 DOI: 10.1021/acs.macromol.1c01408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 12/08/2021] [Indexed: 11/30/2022]
Abstract
Photocurable polymers are used ubiquitously in 3D printing, coatings, adhesives, and composite fillers. In the present work, the free radical polymerization of photocurable compounds is studied using reactive classical molecular dynamics combined with a dynamical approach of the nonequilibrium molecular dynamics (D-NEMD). Different concentrations of radicals and reaction velocities are considered. The mechanical properties of the polymer resulting from 1,6-hexanediol dimethacrylate systems are characterized in terms of viscosity, diffusion constant, and activation energy, whereas the topological ones through the number of cycles (polymer loops) and cyclomatic complexity. Effects like volume shrinkage and delaying of the gel point for increasing monomer concentration are also predicted, as well as the stress-strain curve and Young's modulus. Combining ab initio, reactive molecular dynamics, and the D-NEMD method might lead to a novel and powerful tool to describe photopolymerization processes and to original routes to optimize additive manufacturing methods relying on photosensitive macromolecular systems.
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Affiliation(s)
| | - Adriano Tiribocchi
- Istituto
per le Applicazioni del Calcolo CNR, Via dei Taurini 19, 00185 Rome, Italy
| | - Sauro Succi
- Istituto
per le Applicazioni del Calcolo CNR, Via dei Taurini 19, 00185 Rome, Italy,Center
for Life Nano Science@La Sapienza, Istituto
Italiano di Tecnologia, Viale Regina Elena, 291, 00161 Rome, Italy
| | - Dario Pisignano
- Dipartimento
di Fisica, Università di Pisa, Largo B. Pontecorvo 16 3, 56127 Pisa, Italy,NEST,
Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127 Pisa, Italy
| | - Marco Lauricella
- Istituto
per le Applicazioni del Calcolo CNR, Via dei Taurini 19, 00185 Rome, Italy,
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11
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Drecun O, Striolo A, Bernardini C. Structural and dynamic properties of some aqueous salt solutions. Phys Chem Chem Phys 2021; 23:15224-15235. [PMID: 34235528 DOI: 10.1039/d0cp05331g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aqueous salt solutions are utilized and encountered in wide-ranging technological applications and natural settings. Towards improved understanding of the effect of salts on the dynamic properties of such systems, dilute aqueous salt solutions (up to 1 molar concentration) are investigated here, via experiments and molecular simulations. Four salts are considered: sodium chloride, for which published results are readily available for comparison, ammonium acetate, barium acetate and barium nitrate, for which published data are scarce. In the present work, molecular dynamics (MD) simulations are conducted to quantify viscosity and water self-diffusion coefficients, together with rheometry and Pulsed Field Gradient Spin Echo (PFGSE)-NMR experiments for validation. Simulation predictions are consistent with experimental observations in terms of trend and magnitude of salt-specific effects. Combining insights from the approaches considered, an interpretation of the results is proposed whereby the capacity of salts to influence bulk dynamics arises from their molecular interfacial area and strength of interaction with first hydration-shell water molecules. For the concentration range investigated, the interpretation could be useful in formulating aqueous systems for applications including the manufacturing of advanced catalysts.
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Affiliation(s)
- Olivera Drecun
- Department of Chemical Engineering, University College London, UK.
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12
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Goswami A, Dalal IS, Singh JK. Universal Nucleation Behavior of Sheared Systems. PHYSICAL REVIEW LETTERS 2021; 126:195702. [PMID: 34047572 DOI: 10.1103/physrevlett.126.195702] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 04/15/2021] [Indexed: 06/12/2023]
Abstract
Using molecular simulations and a modified classical nucleation theory, we study the nucleation, under flow, of a variety of liquids: different water models, Lennard-Jones, and hard sphere colloids. Our approach enables us to analyze a wide range of shear rates inaccessible to brute-force simulations. Our results reveal that the variation of the nucleation rate with shear is universal. A simplified version of the theory successfully captures the nonmonotonic temperature dependence of the nucleation behavior, which is shown to originate from the violation of the Stokes-Einstein relation.
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Affiliation(s)
- Amrita Goswami
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Indranil Saha Dalal
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Jayant K Singh
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
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13
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Ge T, Wang J, Robbins MO. Effects of Coarse-Graining on Molecular Simulations of Mechanical Properties of Glassy Polymers. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02467] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ting Ge
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Jiuling Wang
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Mark O. Robbins
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States
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14
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Maffioli L, Clisby N, Frascoli F, Todd BD. The phase space distribution of confined fluids under shear is not fractal. J Chem Phys 2021; 154:094116. [PMID: 33685171 DOI: 10.1063/5.0039192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We analyze the phase-space compression, characteristic of all deterministic, dissipative systems for an inhomogeneous boundary-driven shear fluid via nonequilibrium molecular dynamics simulations. We find that, although the full system undergoes a phase space contraction, the marginal distribution of the fluid particles is described by a smooth, volume preserving probability density function. This is the case for most thermodynamic states of physical interest. Hence, we show that the models currently employed to investigate inhomogeneous fluids in a nonequilibrium steady state, in which only walls are thermostatted, generate a non-singular distribution for the fluid.
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Affiliation(s)
- Luca Maffioli
- Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Nathan Clisby
- Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Federico Frascoli
- Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - B D Todd
- Department of Mathematics, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
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15
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Parisi D, Costanzo S, Jeong Y, Ahn J, Chang T, Vlassopoulos D, Halverson JD, Kremer K, Ge T, Rubinstein M, Grest GS, Srinin W, Grosberg AY. Nonlinear Shear Rheology of Entangled Polymer Rings. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02839] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Daniele Parisi
- FORTH and University of Crete, Heraklion 71110, Greece
- Penn State University, State College, Pennsylvania 16801, United States
| | - Salvatore Costanzo
- FORTH and University of Crete, Heraklion 71110, Greece
- University of Naples Federico II, Naples 80125, Italy
| | - Youncheol Jeong
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - Junyoung Ahn
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - Taihyun Chang
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | | | | | - Kurt Kremer
- Max Planck Institute for Polymer Research, Mainz 55021, Germany
| | - Ting Ge
- University of South Carolina, Columbia, South Carolina 29208-0001, United States
| | - Michael Rubinstein
- Duke University, Durham, North Carolina 27708-9976, United States
- Hokkaido University, Sapporo, Hokkaido 060-0808, Japan
| | - Gary S. Grest
- Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - Watee Srinin
- Naresuan University, Mueang Phitsanulok, Phitsanulok 65000, Thailand
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16
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Goswami A, Singh JK. Homogeneous nucleation of sheared liquids: advances and insights from simulations and theory. Phys Chem Chem Phys 2021; 23:15402-15419. [PMID: 34279013 DOI: 10.1039/d1cp02617h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
One of the most ubiquitous and technologically important phenomena in nature is the nucleation of homogeneous flowing systems. The microscopic effects of shear on a nucleating system are still imperfectly understood, although in recent years a consistent picture has emerged. The opposing effects of shear can be split into two major contributions for simple atomic and molecular liquids: increase of the energetic cost of nucleation, and enhancement of the kinetics. In this perspective, we describe the latest computational and theoretical techniques which have been developed over the past two decades. We collate and unify the overarching influences of shear, temperature, and supersaturation on the process of homogeneous nucleation. Experimental techniques and capabilities are discussed, against the backdrop of results from simulations and theory. Although we primarily focus on simple systems, we also touch upon the sheared nucleation of more complex systems, including glasses and polymer melts. We speculate on the promising directions and possible advances that could come to fruition in the future.
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Affiliation(s)
- Amrita Goswami
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India.
| | - Jayant K Singh
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India.
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17
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Abstract
Both molecular dynamics (MD) and nonequilibrium molecular dynamics (NEMD) simulations were performed to simulate coal ashes using the Guillot-Sator model in this work. The structural and transport properties of coal ashes at high temperatures have been obtained. Superheating of coal ash system with anorthite crystal structure initial configuration has been observed for MD simulation which explains the discrepancy between previous MD simulation results and FactSage thermochemical calculations. The fluxing effects of both calcium oxide and sodium oxide have been investigated systematically through MD and NEMD simulations. Moreover, the viscosities of coal ash systems have been computed by two methods: (1) Stokes-Einstein equation; (2) NEMD simulations. Estimations of viscosities for various coal ash systems based on Stokes-Einstein equation exhibit a strong temperature dependence of viscosity, which agrees with previous experimental results. On the other hand, NEMD simulation results that showed a strong shear-thinning feature, failed to reproduce this strong temperature dependence of viscosity, possibly due to the short simulation time. Nevertheless, NEMD simulations not only provide us detailed information about atoms dynamics under shear, but also allow us to model the coal ash system far from equilibrium which cannot be accessed by thermodynamics calculation using software like FactSage.
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18
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Dai X, Bai J, Yuan P, Du S, Li D, Wen X, Li W. The application of molecular simulation in ash chemistry of coal. Chin J Chem Eng 2020. [DOI: 10.1016/j.cjche.2020.06.024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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19
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Perego A, Khabaz F. Volumetric and Rheological Properties of Vitrimers: A Hybrid Molecular Dynamics and Monte Carlo Simulation Study. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01423] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Alessandro Perego
- Department of Polymer Engineering, The University of Akron, 250 S. Forge Street, Akron, Ohio 44325-0301, United States
| | - Fardin Khabaz
- Department of Polymer Engineering, The University of Akron, 250 S. Forge Street, Akron, Ohio 44325-0301, United States
- Department of Chemical, Biomolecular and Corrosion Engineering, The University of Akron, 250 S. Forge Street, Akron, Ohio 44325-0301, United States
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20
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Goswami A, Dalal IS, Singh JK. Seeding method for ice nucleation under shear. J Chem Phys 2020; 153:094502. [DOI: 10.1063/5.0021206] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Amrita Goswami
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, India
| | - Indranil Saha Dalal
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, India
| | - Jayant K. Singh
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, India
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21
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Razizadeh M, Nikfar M, Paul R, Liu Y. Coarse-Grained Modeling of Pore Dynamics on the Red Blood Cell Membrane under Large Deformations. Biophys J 2020; 119:471-482. [PMID: 32645292 PMCID: PMC7399477 DOI: 10.1016/j.bpj.2020.06.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 05/22/2020] [Accepted: 06/16/2020] [Indexed: 12/17/2022] Open
Abstract
Transient pore formation on the membrane of red blood cells (RBCs) under high mechanical tensions is of great importance in many biomedical applications, such as RBC damage (hemolysis) and mechanoporation-based drug delivery. The dynamic process of pore formation, growth, and resealing is hard to visualize in experiments. We developed a mesoscale coarse-grained model to study the characteristics of transient pores on a patch of the lipid bilayer that is strengthened by an elastic meshwork representing the cytoskeleton. Unsteady molecular dynamics was used to study the pore formation and reseal at high strain rates close to the physiological ranges. The critical strain for pore formation, pore characteristics, and cytoskeleton effects were studied. Results show that the presence of the cytoskeleton increases the critical strain of pore formation and confines the pore growth. Moreover, the pore recovery process under negative strain rates (compression) is analyzed. Simulations show that pores can remain open for a long time during the high-speed tank-treading induced stretching and compression process that a patch of the RBC membrane usually experiences under high shear flow. Furthermore, complex loading conditions can affect the pore characteristics and result in denser pores. Finally, the effects of strain rate on pore formation are analyzed. Higher rate stretching of membrane patch can result in a significant increase in the critical areal strain and density of pores. Such a model reveals the dynamic molecular process of RBC damage in biomedical devices and mechanoporation that, to our knowledge, has not been reported before.
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Affiliation(s)
- Meghdad Razizadeh
- Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania
| | - Mehdi Nikfar
- Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania
| | - Ratul Paul
- Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania
| | - Yaling Liu
- Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania; Department of Bioengineering, Lehigh University, Bethlehem, Pennsylvania.
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22
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Prentice IJ, Liu X, Nerushev OA, Balakrishnan S, Pulham CR, Camp PJ. Experimental and simulation study of the high-pressure behavior of squalane and poly-α-olefins. J Chem Phys 2020; 152:074504. [PMID: 32087637 DOI: 10.1063/1.5139723] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The equation of state, dynamical properties, and molecular-scale structure of squalane and mixtures of poly-α-olefins at room temperature are studied with a combination of state-of-the-art, high-pressure experiments and molecular-dynamics simulations. Diamond-anvil cell experiments indicate that both materials are non-hydrostatic media at pressures above ∼1 GPa. The equation of state does not exhibit any sign of a first-order phase transition. High-pressure x-ray diffraction experiments on squalane show that there are no Bragg peaks, and hence, the apparent solidification occurs without crystallization. These observations are complemented by a survey of the equation of state and dynamical properties using simulations. The results show that molecular diffusion is essentially arrested above about 1 GPa, which supports the hypothesis that the samples are kinetically trapped in metastable amorphous-solid states. The shear viscosity becomes extremely large at very high pressures, and the coefficient governing its increase from ambient pressure is in good agreement with the available literature data. Finally, simulated radial distribution functions are used to explore the evolution of the molecular-scale structure with increasing pressure. Subtle changes in the short-range real-space correlations are related to a collapse of the molecular conformations with increasing pressure, while the evolution of the static structure factor shows excellent correlation with the available x-ray diffraction data. These results are of indirect relevance to oil-based lubricants, as the pressures involved are comparable to those found in engines, and hence, the ability of lubricating thin films to act as load-bearing media can be linked to the solidification phenomena studied in this work.
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Affiliation(s)
- Iain J Prentice
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Xiaojiao Liu
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Oleg A Nerushev
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Sashi Balakrishnan
- Global Lubricants Technology Research and Innovation, BP International Limited, Technology Centre, Whitchurch Hill, Pangbourne, Reading RG8 7QR, England
| | - Colin R Pulham
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
| | - Philip J Camp
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland
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23
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O’Connor TC, Ge T, Rubinstein M, Grest GS. Topological Linking Drives Anomalous Thickening of Ring Polymers in Weak Extensional Flows. PHYSICAL REVIEW LETTERS 2020; 124:027801. [PMID: 32004030 PMCID: PMC7190399 DOI: 10.1103/physrevlett.124.027801] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Indexed: 05/28/2023]
Abstract
Molecular dynamics simulations confirm recent extensional flow experiments showing ring polymer melts exhibit strong extension-rate thickening of the viscosity at Weissenberg numbers Wi≪1. Thickening coincides with the extreme elongation of a minority population of rings that grows with Wi. The large susceptibility of some rings to extend is due to a flow-driven formation of topological links that connect multiple rings into supramolecular chains. Links form spontaneously with a longer delay at lower Wi and are pulled tight and stabilized by the flow. Once linked, these composite objects experience larger drag forces than individual rings, driving their strong elongation. The fraction of linked rings depends nonmonotonically on Wi, increasing to a maximum when Wi∼1 before rapidly decreasing when the strain rate approaches 1/τ_{e}.
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Affiliation(s)
| | - Ting Ge
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, 27708, USA
| | - Michael Rubinstein
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, 27708, USA
| | - Gary S. Grest
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
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24
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O’Connor TC, Hopkins A, Robbins MO. Stress Relaxation in Highly Oriented Melts of Entangled Polymers. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b01161] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Thomas C. O’Connor
- Sandia National Laboratories, Albuquerque, New Mexico 87123, United States
| | - Austin Hopkins
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Mark O. Robbins
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, United States
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25
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Kroonblawd MP, Lindsey RK, Goldman N. Synthesis of functionalized nitrogen-containing polycyclic aromatic hydrocarbons and other prebiotic compounds in impacting glycine solutions. Chem Sci 2019; 10:6091-6098. [PMID: 31360414 PMCID: PMC6585877 DOI: 10.1039/c9sc00155g] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 05/19/2019] [Indexed: 01/09/2023] Open
Abstract
Proteinogenic amino acids can be produced on or delivered to a planet via impacting abiotic sources and consequently were likely present before the emergence of life on Earth. However, the role that these materials played in prebiotic scenarios remains an open question, in part because little is known about the survivability and reactivity of astrophysical organic compounds upon impact with a planetary surface. To this end, we use a force-matched semi-empirical quantum simulation method to study impacts of aqueous proteinogenic amino acids at conditions reaching 48 GPa and 3000 K. Here, we probe a relatively unstudied mechanism for prebiotic synthesis where sudden heating and pressurization causes condensation of complex carbon-rich structures from mixtures of glycine, the simplest protein-forming amino acid. These carbon-containing clusters are stable on short timescales and undergo a fundamental structural transition upon expansion and cooling from predominantly sp3-bonded tetrahedral-like moieties to those that are more sp2-bonded and planar. The recovered sp2-bonded structures include large nitrogen containing polycyclic aromatic hydrocarbons (NPAHs) with a number of different functional groups and embedded bonded regions akin to oligo-peptides. A number of small organic molecules with prebiotic relevance are also predicted to form. This work presents an alternate route to gas-phase synthesis for the formation of NPAHs of high complexity and highlights the significance of both the thermodynamic path and local chemical self-assembly in forming prebiotic species during shock synthesis. Our results help determine the role of comets and other celestial bodies in both the delivery and synthesis of potentially significant life building compounds on early Earth.
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Affiliation(s)
- Matthew P Kroonblawd
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , CA 94550 , USA .
| | - Rebecca K Lindsey
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , CA 94550 , USA .
| | - Nir Goldman
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , CA 94550 , USA .
- Department of Chemical Engineering , University of California , Davis , California 95616 , USA
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26
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Viscosity of a highly compressed methylated alkane via equilibrium and nonequilibrium molecular dynamics simulations. Chem Phys Lett 2019. [DOI: 10.1016/j.cplett.2019.01.041] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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27
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Costigliola L, Heyes DM, Schrøder TB, Dyre JC. Revisiting the Stokes-Einstein relation without a hydrodynamic diameter. J Chem Phys 2019; 150:021101. [PMID: 30646717 DOI: 10.1063/1.5080662] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present diffusion coefficient and shear viscosity data for the Lennard-Jones fluid along nine isochores above the critical density, each involving a temperature variation of roughly two orders of magnitude. The data are analyzed with respect to the Stokes-Einstein (SE) relation, which breaks down gradually at high temperatures. This is rationalized in terms of the fact that the reduced diffusion coefficient D ̃ and the reduced viscosity η ̃ are both constant along the system's lines of constant excess entropy (the isomorphs). As a consequence, D ̃ η ̃ is a function of T/T Ref(ρ) in which T is the temperature, ρ is the density, and T Ref(ρ) is the temperature as a function of the density along a reference isomorph. This allows one to successfully predict the viscosity from the diffusion coefficient in the studied region of the thermodynamic phase diagram.
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Affiliation(s)
- Lorenzo Costigliola
- "Glass and Time," IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
| | - David M Heyes
- Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
| | - Thomas B Schrøder
- "Glass and Time," IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
| | - Jeppe C Dyre
- "Glass and Time," IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
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28
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Song J, Kahraman R, Collinson DW, Xia W, Brinson LC, Keten S. Temperature effects on the nanoindentation characterization of stiffness gradients in confined polymers. SOFT MATTER 2019; 15:359-370. [PMID: 30421764 DOI: 10.1039/c8sm01539b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The stiffening of polymers near inorganic fillers plays an important role in strengthening polymer nanocomposites, and recent advances in metrology have allowed us to sample such effects using local mechanical measurement techniques such as nanoindentation and atomic force microscopy. A general understanding of temperature and confinement effects on the measured stiffness gradient length-scale ξint is lacking however, which convolutes molecular interpretation of local property measurements. Using coarse-grained molecular dynamics and finite element nanoindentation simulations, we show that the measured ξint increases with temperature in highly confined polymer systems, a dependence which acts in the opposite direction in systems with low confinement. These disparate trends are closely related to the polymer's viscoelastic state and the resulting changes in incompressibility and dissipative ability as the polymer transitions from glassy to rubbery. At high temperatures above the glass transition temperature, a geometrically confined system restricts the viscous dissipation of the applied load by the increasingly incompressible polymer. The indentation causes a dramatic build-up of hydrostatic pressure near the confining surface, which contributes to an enlarged measurement of ξint. By contrast, a less-confined system allows the pressure to dissipate via intermolecular motion, thus lowering the measured ξint with increased temperature above the glass transition temperature. These findings suggest that the well-established thin film-nancomposite analogy for polymer mobility near interfaces can be convoluted when measuring local mechanical properties, as the viscoelastic state and geometric confinement of the polymer can affect the nanomechanical response during indentation purely from continuum effects.
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Affiliation(s)
- Jake Song
- Dept. of Materials Science & Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA
| | - Rıdvan Kahraman
- Dept. of Materials Science & Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA
| | - David W Collinson
- Dept. of Mechanical Engineering and Materials Science, Duke University, 144 Hudson Hall, Durham, NC 27708, USA. and Dept. of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA.
| | - Wenjie Xia
- Department of Civil & Environmental Engineering, North Dakota State University, Fargo, ND 58108, USA
| | - L Catherine Brinson
- Dept. of Mechanical Engineering and Materials Science, Duke University, 144 Hudson Hall, Durham, NC 27708, USA. and Center for Hierarchical Materials Design, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA
| | - Sinan Keten
- Dept. of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA. and Dept. of Civil & Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA and Center for Hierarchical Materials Design, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA
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29
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Xing Z, Ness C, Frenkel D, Eiser E. Structural and Linear Elastic Properties of DNA Hydrogels by Coarse-Grained Simulation. Macromolecules 2019. [DOI: 10.1021/acs.macromol.8b01948] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Zhongyang Xing
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Christopher Ness
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom
| | - Daan Frenkel
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Erika Eiser
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
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30
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Dašić M, Stanković I, Gkagkas K. Molecular dynamics investigation of the influence of the shape of the cation on the structure and lubrication properties of ionic liquids. Phys Chem Chem Phys 2019; 21:4375-4386. [DOI: 10.1039/c8cp07364c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A theoretical study of the influence of the geometry of the cation on the response of ionic liquids to confinement and mechanical strain is presented. The specific friction is low and the friction force decreases with tail size. The low hysteretic losses during the linear cyclic motion suggest strong slip inside the gap.
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Affiliation(s)
- Miljan Dašić
- Scientific Computing Laboratory
- Center for the Study of Complex Systems
- Institute of Physics Belgrade
- University of Belgrade
- 11080 Belgrade
| | - Igor Stanković
- Scientific Computing Laboratory
- Center for the Study of Complex Systems
- Institute of Physics Belgrade
- University of Belgrade
- 11080 Belgrade
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31
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Kroonblawd MP, Goldman N, Lewicki JP. Chemical Degradation Pathways in Siloxane Polymers Following Phenyl Excitations. J Phys Chem B 2018; 122:12201-12210. [PMID: 30482015 DOI: 10.1021/acs.jpcb.8b09636] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We use ensembles of quantum-based molecular dynamics simulations to predict the chemical reactions that follow radiation-induced excitations of phenyl groups in a model copolymer of polydimethylsiloxane and polydiphenylsiloxane. Our simulations span a wide range of highly porous and condensed phase densities and include both wet and dry conditions. We observe that in the absence of water, excited phenyl groups tend to abstract hydrogen from other methyl or phenyl side groups to produce benzene, with the under-hydrogenated group initiating subsequent intrachain cyclization reactions. These systems also yield minor products of diphenyl moieties formed by the complete abstraction of both phenyl groups from a single polydiphenylsiloxane subunit. In contrast, we find that the presence of water promotes the formation of free benzene and silanol side groups, reduces the likelihood for intrachain cyclization reactions, and completely suppresses the formation of diphenyl species. In addition, we predict that water plays a critical role in chain scission reactions, which indicates a possible synergistic effect between environmental moisture and radiation that could promote alterations of a larger polymer network. These results could have impact in interpreting accelerated aging experiments, where polymer decomposition reactions and network rearrangements are thought to have a significant effect on the ensuing mechanical properties.
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Affiliation(s)
- Matthew P Kroonblawd
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , California 94550 , United States
| | - Nir Goldman
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , California 94550 , United States.,Department of Chemical Engineering , University of California, Davis , Davis , California 95616 , United States
| | - James P Lewicki
- Physical and Life Sciences Directorate , Lawrence Livermore National Laboratory , Livermore , California 94550 , United States
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32
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Dašić M, Stanković I, Gkagkas K. Influence of confinement on flow and lubrication properties of a salt model ionic liquid investigated with molecular dynamics. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2018; 41:130. [PMID: 30377867 DOI: 10.1140/epje/i2018-11740-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 10/09/2018] [Indexed: 06/08/2023]
Abstract
We present a molecular dynamics study of the effects of confinement on the lubrication and flow properties of ionic liquids. We use a coarse-grained salt model description of ionic liquid as a lubricant confined between finite solid plates and subjected to two dynamic regimes: shear and cyclic loading. The impact of confinement on the ion arrangement and mechanical response of the system has been studied in detail and compared to static and bulk properties. The results have revealed that the wall slip has a profound influence on the force built-up as a response to mechanical deformation and that at the same time in the dynamic regime interaction with the walls represents a principal driving force governing the behaviour of ionic liquid in the gap. We also observe a transition from a dense liquid to an ordered and potentially solidified state of the ionic liquid taking place under variable normal loads and under shear.
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Affiliation(s)
- Miljan Dašić
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080, Belgrade, Serbia.
| | - Igor Stanković
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080, Belgrade, Serbia
| | - Konstantinos Gkagkas
- Advanced Technology Division, Toyota Motor Europe NV/SA, Technical Center, Hoge Wei 33B, 1930, Zaventem, Belgium
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33
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Scotti A, Brugnoni M, Rudov AA, Houston JE, Potemkin II, Richtering W. Hollow microgels squeezed in overcrowded environments. J Chem Phys 2018; 148:174903. [DOI: 10.1063/1.5026100] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- A. Scotti
- Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany
| | - M. Brugnoni
- Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany
| | - A. A. Rudov
- Physics Department, Lomonosov Moscow State University, 119991 Moscow, Russian Federation
- DWI–Leibniz Institute for Interactive Materials e.V., Aachen 52056, Germany
| | - J. E. Houston
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstr. 1, 85748 Garching, Germany
| | - I. I. Potemkin
- Physics Department, Lomonosov Moscow State University, 119991 Moscow, Russian Federation
- DWI–Leibniz Institute for Interactive Materials e.V., Aachen 52056, Germany
- National Research South Ural State University, Chelyabinsk 454080, Russian Federation
| | - W. Richtering
- Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany
- JARA-SOFT, 52056 Aachen, Germany
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34
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Shebert GL, Joo YL. Simultaneous uniaxial extensional deformation and cylindrical confinement of block copolymers using non-equilibrium molecular dynamics. SOFT MATTER 2018; 14:1389-1396. [PMID: 29383370 DOI: 10.1039/c7sm01889d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Using coarse-grained nonequilibrium molecular dynamics, symmetric block copolymers are simulated under the combined effects of cylindrical confinement and uniaxial extensional deformation. For a given confinement diameter, a block copolymer (BCP) will self-assemble into a fixed number of concentric cylinder lamellae at equilibrium. The changing diameter during uniaxial extensional deformation therefore is expected to affect the morphology of the BCPs. The aim of this study is to investigate the interplay of deformation and confinement on BCP morphology by varying the simulation strain rate and diameter. Two different simulation approaches are conducted: constant time simulations with varying initial diameter and constant strain simulations with varying simulation time. A comparison of self-assembly at different strain rates shows that for low strain rates, near-equilibrium morphology can form despite the deformation, while for progressively higher strain rates, extra lamellae and disordered morphologies appear. By defining a Weissenberg number based on the deformation and polymer self-assembly time-scales, the morphologies at different strain rates and diameters are explained. Using the time scale analysis, ordered morphologies appear for Wi < 1, while extra lamellae and disordered morphologies occur at Wi > 1. For the latter case, the cylinder diameter shrinks too quickly for polymers to form the equilibrium morphology, which results in a mixture of lamellar structures along the cylinder length.
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Affiliation(s)
- George L Shebert
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA.
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35
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Lukose B, Bobbili SV, Clancy P. Factors affecting tacticity and aggregation of P3HT polymers in P3HT:PCBM blends. MOLECULAR SIMULATION 2017. [DOI: 10.1080/08927022.2017.1303688] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Binit Lukose
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Sai Vineeth Bobbili
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Paulette Clancy
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
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36
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Shen Z, Röding M, Kröger M, Li Y. Carbon Nanotube Length Governs the Viscoelasticity and Permeability of Buckypaper. Polymers (Basel) 2017; 9:E115. [PMID: 30970795 PMCID: PMC6431842 DOI: 10.3390/polym9040115] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 01/27/2023] Open
Abstract
The effects of carbon nanotube (CNT) length on the viscoelasticity and permeability of buckypaper, composed of (5,5) single-walled CNTs (SWCNTs), are systematically explored through large-scale coarse-grained molecular dynamics simulations. The SWCNT length is found to have a pronounced impact on the structure of buckypapers. When the SWCNTs are short, they are found to form short bundles and to be tightly packed, exhibit high density and small pores, while long SWCNTs are entangled together at a low density accompanied by large pores. These structure variations contribute to distinct performances in the viscoelasticity of buckypapers. The energy dissipation for buckypapers with long SWCNTs under cyclic shear loading is dominated by the attachment and detachment between SWCNTs through a zipping-unzipping mechanism. Thus, the viscoelastic characteristics of buckypapers, such as storage and loss moduli, demonstrate frequency- and temperature-independent behaviors. In contrast, the sliding-friction mechanism controls the energy dissipation between short SWCNTs when the buckypaper is under loading and unloading processes. Friction between short SWCNTs monotonically increases with rising length of SWCNTs and temperature. Therefore, the tan δ , defined as the ratio of the loss modulus over the storage modulus, of buckypaper with short SWCNTs also increases with the increment of temperature or SWCNT length, before the SWCNTs are entangled together. The permeability of buckypapers is further investigated by studying the diffusion of structureless particles within buckypapers, denoted by the obstruction factor ( β ). It is found to be linearly dependent on the volume fraction of SWCNTs, signifying a mass-dominated permeability, regardless of the structure variations induced by different SWCNT lengths. The present study provides a comprehensive picture of the structure-property relationship for buckypapers composed of SWCNTs. The methodology could be used for designing multifunctional buckypaper-based devices.
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Affiliation(s)
- Zhiqiang Shen
- Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA.
| | - Magnus Röding
- RISE Bioscience and Materials, Box 5401, 402 29 Göteborg, Sweden.
- School of Energy and Resources, UCL Australia, University College London, Adelaide SA 5000, Australia.
| | - Martin Kröger
- Polymer Physics, Department of Materials, ETH Zürich, CH-8093 Zurich, Switzerland.
| | - Ying Li
- Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA.
- Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA.
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Shebert GL, Lak Joo Y. Effect of elongational flow on immiscible polymer blend/nanoparticle composites: a molecular dynamics study. SOFT MATTER 2016; 12:6132-6140. [PMID: 27356215 DOI: 10.1039/c6sm00619a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Using coarse-grained nonequilibrium molecular dynamics, the dynamics of a blend of the equal ratio of immiscible polymers mixed with nanoparticles (NP) are simulated. The simulations are conducted under planar elongational flow, which affects the dispersion of the NPs and the self-assembly morphology. The goal of this study is to investigate the effect of planar elongational flow on the nanocomposite blend system as well as to thoroughly compare the blend to an analogous symmetric block copolymer (BCP) system to understand the role of the polymer structure on the morphology and NP dispersion. Two types of spherical NPs are considered: (1) selective NPs that are attracted to one of the polymer components and (2) nonselective NPs that are neutral to both components. A comparison of the blend and BCP systems reveals that for selective NP, the blend system shows a much broader NP distribution in the selective phase than the BCP phase. This is due to a more uniform distribution of polymer chain ends throughout the selective phase in the blend system than the BCP system. For nonselective NP, the blend and BCP systems show similar results for low elongation rates, but the NP peak in the BCP system broadens as elongation rates approach the order-disorder transition. In addition, the presence of NP is found to affect the morphology transitions of both the blend and BCP systems, depending on the NP type.
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Affiliation(s)
- George L Shebert
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
| | - Yong Lak Joo
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
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Costigliola L, Schrøder TB, Dyre JC. Freezing and melting line invariants of the Lennard-Jones system. Phys Chem Chem Phys 2016; 18:14678-90. [PMID: 27186598 DOI: 10.1039/c5cp06363a] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The invariance of several structural and dynamical properties of the Lennard-Jones (LJ) system along the freezing and melting lines is interpreted in terms of isomorph theory. First the freezing/melting lines of the LJ system are shown to be approximated by isomorphs. Then we show that the invariants observed along the freezing and melting isomorphs are also observed on other isomorphs in the liquid and crystalline phases. The structure is probed by the radial distribution function and the structure factor and dynamics are probed by the mean-square displacement, the intermediate scattering function, and the shear viscosity. Studying these properties with reference to isomorph theory explains why the known single-phase melting criteria hold, e.g., the Hansen-Verlet and the Lindemann criteria, and why the Andrade equation for the viscosity at freezing applies, e.g., for most liquid metals. Our conclusion is that these empirical rules and invariants can all be understood from isomorph theory and that the invariants are not peculiar to the freezing and melting lines, but hold along all isomorphs.
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Affiliation(s)
- Lorenzo Costigliola
- "Glass and Time", IMFUFA, Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark.
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39
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Jhon YI, Kim C, Seo M, Cho WJ, Lee S, Jhon YM. Tensile Characterization of Single-Walled Carbon Nanotubes with Helical Structural Defects. Sci Rep 2016; 6:20324. [PMID: 26841708 PMCID: PMC4740892 DOI: 10.1038/srep20324] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 12/30/2015] [Indexed: 12/21/2022] Open
Abstract
Recently, evidence was presented that certain single-walled carbon nanotubes (SWNTs) possess helical defective traces, exhibiting distinct cleaved lines, yet their mechanical characterization remains a challenge. On the basis of the spiral growth model of SWNTs, here we present atomic details of helical defects and investigate how the tensile behaviors of SWNTs change with their presence using molecular dynamics simulations. SWNTs have exhibited substantially lower tensile strength and strain than theoretical results obtained from a seamless tubular structure, whose physical origin cannot be explained either by any known SWNT defects so far. We find that this long-lasting puzzle could be explained by assuming helical defects in SWNTs, exhibiting excellent agreement with experimental observation. The mechanism of this tensile process is elucidated by analyzing atomic stress distribution and evolution, and the effects of the chirality and diameter of SWNTs on this phenomenon are examined based on linear elastic fracture mechanics. This work contributes significantly to our understanding of the growth mechanism, defect hierarchies, and mechanical properties of SWNTs.
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Affiliation(s)
- Young I. Jhon
- Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Chulki Kim
- Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Minah Seo
- Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Woon Jo Cho
- Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Seok Lee
- Center for Opto-Electronic Conversion System, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Young Min Jhon
- Sensor System Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
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40
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Toughness and strength of nanocrystalline graphene. Nat Commun 2016; 7:10546. [PMID: 26817712 PMCID: PMC4738364 DOI: 10.1038/ncomms10546] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 12/23/2015] [Indexed: 12/22/2022] Open
Abstract
Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. However, graphene made with scalable fabrication techniques is polycrystalline and contains inherent nanoscale line and point defects—grain boundaries and grain-boundary triple junctions—that lead to significant statistical fluctuations in toughness and strength. These fluctuations become particularly pronounced for nanocrystalline graphene where the density of defects is high. Here we use large-scale simulation and continuum modelling to show that the statistical variation in toughness and strength can be understood with ‘weakest-link' statistics. We develop the first statistical theory of toughness in polycrystalline graphene, and elucidate the nanoscale origins of the grain-size dependence of its strength and toughness. Our results should lead to more reliable graphene device design, and provide a framework to interpret experimental results in a broad class of two-dimensional materials. Graphene is known to be a remarkably strong material, but it can often contain defects. Here, the authors use large-scale simulations and continuum modelling to show that the statistical variation in toughness and strength of polycrystalline graphene can be understood with 'weakest-link' statistics.
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41
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Hunt TA. Periodic boundary conditions for the simulation of uniaxial extensional flow of arbitrary duration. MOLECULAR SIMULATION 2015. [DOI: 10.1080/08927022.2015.1051043] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Petersen CF, Evans DJ, Williams SR. The instantaneous fluctuation theorem. J Chem Phys 2013; 139:184106. [PMID: 24320253 DOI: 10.1063/1.4829445] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We give a derivation of a new instantaneous fluctuation relation for an arbitrary phase function which is odd under time reversal. The form of this new relation is not obvious, and involves observing the system along its transient phase space trajectory both before and after the point in time at which the fluctuations are being compared. We demonstrate this relation computationally for a number of phase functions in a shear flow system and show that this non-locality in time is an essential component of the instantaneous fluctuation theorem.
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Affiliation(s)
- Charlotte F Petersen
- Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
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43
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Hartkamp R, Todd BD, Luding S. A constitutive framework for the non-Newtonian pressure tensor of a simple fluid under planar flows. J Chem Phys 2013; 138:244508. [DOI: 10.1063/1.4810746] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Suzuki K, Hayakawa H. Nonequilibrium mode-coupling theory for uniformly sheared underdamped systems. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:012304. [PMID: 23410328 DOI: 10.1103/physreve.87.012304] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Revised: 12/13/2012] [Indexed: 06/01/2023]
Abstract
Nonequilibrium mode-coupling theory (MCT) for uniformly sheared underdamped systems is developed, starting from the microscopic thermostated Sllod equation and the corresponding Liouville equation. Special attention is paid to the translational invariance in the sheared frame, which requires an appropriate definition of the transient time correlators. The derived MCT equation satisfies the alignment of the wave vectors and is manifestly translationally invariant. Isothermal condition is implemented by the introduction of current fluctuation in the dissipative coupling to the thermostat. This current fluctuation grows in the α relaxation regime, which generates a pronounced relaxation of the yield stress compared to the overdamped case. This result fills the gap between the molecular dynamics simulation and the overdamped MCT reported previously. The response to a perturbation of the shear rate demonstrates an inertia effect which is not observed in the overdamped case. Our theory turns out to be a nontrivial extension of the theory by Fuchs and Cates [J. Rheol. 53, 957 (2009)] to underdamped systems. Since our starting point is identical to that of Chong and Kim [Phys. Rev. E 79, 021203 (2009)], the contradictions between Fuchs-Cates and Chong-Kim are resolved.
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Affiliation(s)
- Koshiro Suzuki
- Analysis Technology Development Center, Canon Inc., 30-2 Shimomaruko 3-chome, Tokyo 146-8501, Japan.
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45
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Bernardi S, Brookes SJ, Searles DJ, Evans DJ. Response theory for confined systems. J Chem Phys 2012; 137:074114. [DOI: 10.1063/1.4746121] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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46
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Hartkamp R, Bernardi S, Todd BD. Transient-time correlation function applied to mixed shear and elongational flows. J Chem Phys 2012; 136:064105. [PMID: 22360167 DOI: 10.1063/1.3684753] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The transient-time correlation function (TTCF) method is used to calculate the nonlinear response of a homogeneous atomic fluid close to equilibrium. The TTCF response of the pressure tensor subjected to a time-independent planar mixed flow of shear and elongation is compared to directly averaged non-equilibrium molecular dynamics (NEMD) simulations. We discuss the consequence of noise in simulations with a small rate of deformation. The generalized viscosity for planar mixed flow is also calculated with TTCF. We find that for small rates of deformation, TTCF is far more efficient than direct averages of NEMD simulations. Therefore, TTCF can be applied to fluids with deformation rates which are much smaller than those commonly used in NEMD simulations. Ultimately, TTCF applied to molecular systems is amenable to direct comparison between NEMD simulations and experiments and so in principle can be used to study the rheology of polymer melts in industrial processes.
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Affiliation(s)
- Remco Hartkamp
- Multi Scale Mechanics, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
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Evans DJ, Williams SR, Searles DJ. On the entropy of relaxing deterministic systems. J Chem Phys 2011; 135:194107. [DOI: 10.1063/1.3660203] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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48
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Hunt TA, Bernardi S, Todd BD. A new algorithm for extended nonequilibrium molecular dynamics simulations of mixed flow. J Chem Phys 2010; 133:154116. [PMID: 20969379 DOI: 10.1063/1.3489683] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this work, we develop a new algorithm for nonequilibrium molecular dynamics of fluids under planar mixed flow, a linear combination of planar elongational flow and planar Couette flow. To date, the only way of simulating mixed flow using nonequilibrium molecular dynamics techniques was to impose onto the simulation box irreversible transformations. This would bring the simulation to an end as soon as the minimum lattice space requirements were violated. In practical terms, this meant repeating the short simulations to improve statistics and extending the box dimensions to increase the total simulation time. Our method, similar to what has already been done for pure elongational flow, allows a cuboid box to deform in time following the streamlines of the mixed flow and, after a period of time determined by the elongational field, to be mapped back and recover its initial shape. No discontinuity in physical properties is present during the mapping and the simulation can, in this way, be extended indefinitely. We also show that the most general form of mixed flow, in which the angle between the expanding (or contracting) direction and the velocity gradient axis varies, can be cast in a so-called canonical form, in which the angle assumes values that are multiples of π (when a mixed flow exists), by an appropriate choice of the field parameters.
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Affiliation(s)
- Thomas A Hunt
- Computational Biophysics, University of Twente, P.O; Box 217, 7500 AE Enschede, The Netherlands.
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49
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Bernardi S, Todd BD, Hansen JS, Searles DJ, Frascoli F. Lyapunov spectra and conjugate-pairing rule for confined atomic fluids. J Chem Phys 2010; 132:244508. [DOI: 10.1063/1.3446809] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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50
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Chong SH, Otsuki M, Hayakawa H. Generalized Green-Kubo relation and integral fluctuation theorem for driven dissipative systems without microscopic time reversibility. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:041130. [PMID: 20481700 DOI: 10.1103/physreve.81.041130] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 10/29/2009] [Indexed: 05/29/2023]
Abstract
We derive the generalized Green-Kubo relation and an integral form of the fluctuation theorem that apply to driven dissipative systems, in which time-reversal symmetry or local detailed balance is broken. Uniformly sheared granular systems and driven inelastic Lorentz-gas model are considered as examples. It is discussed how statistical mechanical theory dealing with nonequilibrium steady-state properties can be constructed for such systems for which equilibrium state does not exist.
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Affiliation(s)
- Song-Ho Chong
- Institute for Molecular Science, Okazaki 444-8585, Japan
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