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Bera PK, Medvedev GA, Caruthers JM, Ediger MD. Structural Relaxation Time of a Polymer Glass during Deformation. PHYSICAL REVIEW LETTERS 2024; 132:208101. [PMID: 38829058 DOI: 10.1103/physrevlett.132.208101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2023] [Accepted: 04/18/2024] [Indexed: 06/05/2024]
Abstract
In order to determine the structural relaxation time of a polymer glass during deformation, a strain rate switching experiment is performed in the steady-state plastic flow regime. A lightly cross-linked poly(methylmethacrylate) glass was utilized and, simultaneously, the segmental motion in the glass was quantified using an optical probe reorientation method. After the strain rate switch, a nonmonotonic stress response is observed, consistent with previous work. The correlation time for segmental motion, in contrast, monotonically evolves toward a new steady state, providing an unambiguous measurement of the structural relaxation time during deformation, which is found to be approximately equal to the segmental correlation time. The Chen-Schweizer model qualitatively predicts the changes in the segmental correlation time and the observed nonmonotonic stress response. In addition, our experiments are reasonably consistent with the material time assumption used in polymer deformation modeling; in this approach, the response of a polymer glass to a large deformation is described by combining a linear-response model with a time-dependent segmental correlation time.
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Affiliation(s)
- Pradip K Bera
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | | | | | - Mark D Ediger
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Xiao H, Zhang G, Yang E, Ivancic R, Ridout S, Riggleman R, Durian DJ, Liu AJ. Identifying microscopic factors that influence ductility in disordered solids. Proc Natl Acad Sci U S A 2023; 120:e2307552120. [PMID: 37812709 PMCID: PMC10589640 DOI: 10.1073/pnas.2307552120] [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: 05/09/2023] [Accepted: 08/16/2023] [Indexed: 10/11/2023] Open
Abstract
There are empirical strategies for tuning the degree of strain localization in disordered solids, but they are system-specific and no theoretical framework explains their effectiveness or limitations. Here, we study three model disordered solids: a simulated atomic glass, an experimental granular packing, and a simulated polymer glass. We tune each system using a different strategy to exhibit two different degrees of strain localization. In tandem, we construct structuro-elastoplastic (StEP) models, which reduce descriptions of the systems to a few microscopic features that control strain localization, using a machine learning-based descriptor, softness, to represent the stability of the disordered local structure. The models are based on calculated correlations of softness and rearrangements. Without additional parameters, the models exhibit semiquantitative agreement with observed stress-strain curves and softness statistics for all systems studied. Moreover, the StEP models reveal that initial structure, the near-field effect of rearrangements on local structure, and rearrangement size, respectively, are responsible for the changes in ductility observed in the three systems. Thus, StEP models provide microscopic understanding of how strain localization depends on the interplay of structure, plasticity, and elasticity.
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Affiliation(s)
- Hongyi Xiao
- Department of Physics, University of Pennsylvania, Philadelphia, PA19104
- Chemical and Biological Engineering, Institute for Multiscale Simulation, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen91058, Germany
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI48109
| | - Ge Zhang
- Department of Physics, University of Pennsylvania, Philadelphia, PA19104
- Department of Physics, City University of Hong Kong, Hong Kong999077, China
| | - Entao Yang
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA19104
| | - Robert Ivancic
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD20899
| | - Sean Ridout
- Department of Physics, University of Pennsylvania, Philadelphia, PA19104
- Department of Physics, Emory University, Atlanta, GA30322
| | - Robert Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA19104
| | - Douglas J. Durian
- Department of Physics, University of Pennsylvania, Philadelphia, PA19104
- Center for Computational Biology, Flatiron Institute, Simons Foundation, New York, NY10010
| | - Andrea J. Liu
- Department of Physics, University of Pennsylvania, Philadelphia, PA19104
- Center for Computational Biology, Flatiron Institute, Simons Foundation, New York, NY10010
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Yang E, Pressly JF, Natarajan B, Colby R, Winey KI, Riggleman RA. Understanding creep suppression mechanisms in polymer nanocomposites through machine learning. SOFT MATTER 2023; 19:7580-7590. [PMID: 37755065 DOI: 10.1039/d3sm00898c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/28/2023]
Abstract
While recent efforts have shown how local structure plays an essential role in the dynamic heterogeneity of homogeneous glass-forming materials, systems containing interfaces such as thin films or composite materials remain poorly understood. It is known that interfaces perturb the molecular packing nearby, however, numerous studies show the dynamics are modified over a much larger range. Here, we examine the dynamics in polymer nanocomposites (PNCs) using a combination of simulations and experiments and quantitatively separate the role of polymer packing from other effects on the dynamics, as a function of distance from the nanoparticle surfaces. After showing good qualitative agreement between the simulations and experiments in glassy structure and creep compliance, we use a machine-learned structure indicator, softness, to decompose polymer dynamics in our simulated PNCs into structure-dependent and structure-independent processes. With this decomposition, the free energy barrier for polymer rearrangement can be described as a combination of packing-dependent and packing-independent barriers. We find both barriers are higher near nanoparticles and decrease with applied stress, quantitatively demonstrating that the slow interfacial dynamics is not solely due to polymer packing differences, but also the change of structure-dynamics relationships. Finally, we present how this decomposition can be used to accurately predict strain-time creep curves for PNCs from their static configuration, providing additional insights into the effects of polymer-nanoparticle interfaces on creep suppression in PNCs.
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Affiliation(s)
- Entao Yang
- Department of Chemical & Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - James F Pressly
- Department of Materials Science & Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Bharath Natarajan
- ExxonMobil Technology and Engineering Company, Annandale, NJ 08801, USA
| | - Robert Colby
- ExxonMobil Technology and Engineering Company, Annandale, NJ 08801, USA
| | - Karen I Winey
- Department of Chemical & Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
- Department of Materials Science & Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Robert A Riggleman
- Department of Chemical & Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
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Perego A, Khabaz F. Creep and Recovery Behavior of Vitrimers with Fast Bond Exchange Rate. Macromol Rapid Commun 2023; 44:e2200313. [PMID: 35856395 DOI: 10.1002/marc.202200313] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 06/07/2022] [Indexed: 01/11/2023]
Abstract
Vitrimers encompass the desirable mechanical properties of thermosets with the recyclability of thermoplastics. This ability arises from the rearrangement of the vitrimer covalent network upon heating via a bond shuffling mechanism while its cross-link density remains preserved. This unique feature makes vitrimers interesting candidates for the design of materials that combine dimensional stability at high temperatures and solvent resistance with the ability to be reshaped and processed. Despite these advantages, vitrimer exhibits significant creep at operating conditions where thermosets show little or no creep. As the mechanical properties of vitrimers not only depend on their chemical composition but also on the dynamics of the polymer chains, molecular dynamics (MD) simulations can provide detailed molecular mechanisms of the system of interest under macroscopic stress-induced deformations. In this regard, the recently developed MD/Monte Carlo simulation methodology capable of capturing the bond exchange mechanics in vitrimers is used to study the creep and recovery response of a coarse-grained model thermoset and vitrimer with a fast bond exchange rate. The time-stress superposition principle is then successfully applied to the creep response. The resulting universal curves enable us to predict the long-time creep behavior of both systems extending the timescale from 4 to over 10 orders of magnitude.
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Affiliation(s)
- Alessandro Perego
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH, 44325, USA
| | - Fardin Khabaz
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH, 44325, USA.,Department of Chemical, Biomolecular, and Corrosion Engineering, The University of Akron, Akron, OH, 44325, USA
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Razavi M, Xing E, Ediger MD. Overaging with Stress in Polymer Glasses? Faster Segmental Dynamics despite Larger Yield Stress! Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Masoud Razavi
- Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States
| | - Enran Xing
- Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States
| | - M. D. Ediger
- Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States
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