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Nie W, Douglas JF, Xia W. Competing Effects of Molecular Additives and Cross-Link Density on the Segmental Dynamics and Mechanical Properties of Cross-Linked Polymers. ACS ENGINEERING AU 2023; 3:512-526. [PMID: 38144677 PMCID: PMC10739619 DOI: 10.1021/acsengineeringau.3c00043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 09/30/2023] [Accepted: 10/06/2023] [Indexed: 12/26/2023]
Abstract
The introduction of molecular additives into thermosets often results in changes in their dynamics and mechanical properties that can have significant ramifications for diverse applications of this broad class of materials such as coatings, high-performance composites, etc. Currently, there is limited fundamental understanding of how such additives influence glass formation in these materials, a problem of broader significance in glass-forming materials. To address this fundamental problem, here, we employ a simplified coarse-grained (CG) model of a polymer network as a model of thermoset materials and then introduce a polymer additive having the same inherent rigidity and polymer-polymer interaction strength as the cross-linked polymer matrix. This energetically "neutral" or "self-plasticizing" additive model gives rise to non-trivial changes in the dynamics of glass formation and provides an important theoretical reference point for the technologically more important case of interacting additives. Based on this rather idealized model, we systematically explore the combined effect of varying the additive mass percentage (m) and cross-link density (c) on the segmental relaxation dynamics and mechanical properties of a model thermoset material with additives. We find that increasing the additive mass percentage m progressively decreases both the glass-transition temperature Tg and the fragility of glass formation, a trend opposite to increasing c so that these thermoset variables clearly have a competing effect on glass formation in these model materials. Moreover, basic mechanical properties (i.e., bulk, shear, and tensile moduli) likewise exhibit a competitive variation with the increase of m and c, which are strongly correlated with the Debye-Waller parameter ⟨u2⟩, a measure of material stiffness at a molecular scale. Our findings prove beneficial in the development of structure-property relationships for the cross-linked polymers, which could help guide the design of such network materials with tailored physical properties.
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Affiliation(s)
- Wenjian Nie
- Department
of Civil, Construction and Environmental Engineering, North Dakota State University, Fargo, North Dakota 58108, United States
| | - Jack F. Douglas
- Materials
Science and Engineering Division, National
Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Wenjie Xia
- Department
of Aerospace Engineering, Iowa State University, Ames, Iowa 50011, United States
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2
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Zheng X, Guo Y, Douglas JF, Xia W. Competing Effects of Cohesive Energy and Cross-Link Density on the Segmental Dynamics and Mechanical Properties of Cross-Linked Polymers. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Xiangrui Zheng
- Department of Mechanics, School of Physical Science and Engineering, Beijing Jiaotong Uiversity, Beijing, 100044, China
| | - Yafang Guo
- Department of Mechanics, School of Physical Science and Engineering, Beijing Jiaotong Uiversity, Beijing, 100044, China
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Wenjie Xia
- Department of Civil, Construction and Environmental Engineering, North Dakota State University, Fargo, North Dakota 58108, United States
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Zheng X, Guo Y, Douglas JF, Xia W. Understanding the role of cross-link density in the segmental dynamics and elastic properties of cross-linked thermosets. J Chem Phys 2022; 157:064901. [PMID: 35963735 DOI: 10.1063/5.0099322] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Cross-linking is known to play a pivotal role in the relaxation dynamics and mechanical properties of thermoset polymers, which are commonly used in structural applications because of their light weight and inherently strong nature. Here, we employ a coarse-grained (CG) polymer model to systematically explore the effect of cross-link density on basic thermodynamic properties as well as corresponding changes in the segmental dynamics and elastic properties of these network materials upon approaching their glass transition temperatures (Tg). Increasing the cross-link density unsurprisingly leads to a significant slowing down of the segmental dynamics, and the fragility K of glass formation shifts in lockstep with Tg, as often found in linear polymer melts when the polymer mass is varied. As a consequence, the segmental relaxation time τα becomes almost a universal function of reduced temperature, (T - Tg)/Tg, a phenomenon that underlies the applicability of the "universal" Williams-Landel-Ferry (WLF) relation to many polymer materials. We also test a mathematical model of the temperature dependence of the linear elastic moduli based on a simple rigidity percolation theory and quantify the fluctuations in the local stiffness of the network material. The moduli and distribution of the local stiffness likewise exhibit a universal scaling behavior for materials having different cross-link densities but fixed (T - Tg)/Tg. Evidently, Tg dominates both τα and the mechanical properties of our model cross-linked polymer materials. Our work provides physical insights into how the cross-link density affects glass formation, aiding in the design of cross-linked thermosets and other structurally complex glass-forming materials.
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Affiliation(s)
- Xiangrui Zheng
- Department of Mechanics, School of Physical Science and Engineering, Beijing Jiaotong University, Beijing 100044, China
| | - Yafang Guo
- Department of Mechanics, School of Physical Science and Engineering, Beijing Jiaotong University, Beijing 100044, China
| | - Jack F Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Wenjie Xia
- Department of Civil, Construction and Environmental Engineering, North Dakota State University, Fargo, North Dakota 58108, USA
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Chandran S, Baschnagel J, Cangialosi D, Fukao K, Glynos E, Janssen LMC, Müller M, Muthukumar M, Steiner U, Xu J, Napolitano S, Reiter G. Processing Pathways Decide Polymer Properties at the Molecular Level. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b01195] [Citation(s) in RCA: 81] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
| | - Jörg Baschnagel
- Institut Charles Sadron, Université de Strasbourg & CNRS, 23 rue du Loess, 67034 Cedex, Strasbourg, France
| | - Daniele Cangialosi
- Centro de Física de Materiales CFM (CSIC-UPV/EHU) and Materials Physics Center MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 San Sebastin, Spain
| | - Koji Fukao
- Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
| | - Emmanouil Glynos
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P.O.
Box 1385, 711 10 Heraklion, Crete, Greece
| | - Liesbeth M. C. Janssen
- Theory of Polymers and Soft Matter, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August-Universität, Göttingen, Germany
| | - Murugappan Muthukumar
- Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Ullrich Steiner
- Adolphe Merkle Institute, Chemin des Verdiers 4, 1700 Fribourg, Switzerland
| | - Jun Xu
- Advanced Materials Laboratory of Ministry of Education, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
| | - Simone Napolitano
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics, Faculté des Sciences, Université libre de Bruxelles (ULB), CP223, Boulevard du Triomphe, Bruxelles 1050, Belgium
| | - Günter Reiter
- Institute of Physics, University of Freiburg, Freiburg 79104, Germany
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5
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Vogt BD. Mechanical and viscoelastic properties of confined amorphous polymers. ACTA ACUST UNITED AC 2017. [DOI: 10.1002/polb.24529] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Bryan D. Vogt
- Department of Polymer Engineering; University of Akron; Akron Ohio 44325
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Lee S, Lyulin AV, Frank CW, Yoon DY. Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations. POLYMER 2017. [DOI: 10.1016/j.polymer.2017.02.078] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Vignaud G, S Chebil M, Bal JK, Delorme N, Beuvier T, Grohens Y, Gibaud A. Densification and depression in glass transition temperature in polystyrene thin films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:11599-608. [PMID: 25209183 DOI: 10.1021/la501639z] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Ellipsometry and X-ray reflectivity were used to characterize the mass density and the glass transition temperature of supported polystyrene (PS) thin films as a function of their thickness. By measuring the critical wave vector (qc) on the plateau of total external reflection, we evidence that PS films get denser in a confined state when the film thickness is below 50 nm. Refractive indices (n) and electron density profiles measurements confirm this statement. The density of a 6 nm (0.4 gyration radius, Rg) thick film is 30% greater than that of a 150 nm (10Rg) film. A depression of 25 °C in glass transition temperature (Tg) was revealed as the film thickness is reduced. In the context of the free volume theory, this result seems to be in apparent contradiction with the fact that thinner films are denser. However, as the thermal expansion of thinner films is found to be greater than the one of thicker films, the increase in free volume is larger for thin films when temperature is raised. Therefore, the free volume reaches a critical value at a lower Tg for thinner films. This critical value corresponds to the onset of large cooperative movements of polymer chains. The link between the densification of ultrathin films and the drop in their Tg is thus reconciled. We finally show that at their respective Tg(h) all films exhibit a critical mass density of about 1.05 g/cm(3) whatever their thickness. The thickness dependent thermal expansion related to the free volume is consequently a key factor to understand the drop in the Tg of ultrathin films.
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Affiliation(s)
- G Vignaud
- Université Bretagne-Sud , EA 4250, LIMATB, F-56100 Lorient, France
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Inoue R, Kawashima K, Matsui K, Kanaya T, Nishida K, Matsuba G, Hino M. Distributions of glass-transition temperature and thermal expansivity in multilayered polystyrene thin films studied by neutron reflectivity. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:021801. [PMID: 21405853 DOI: 10.1103/physreve.83.021801] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2010] [Indexed: 05/26/2023]
Abstract
We performed neutron reflectivity measurements on multilayered polymer thin films consisting of alternatively stacked deuterated polystyrene (d-PS) and hydrogenated polystyrene (h-PS) layers ∼200 Å thick as a function of temperature covering the glass-transition temperature T(g), and we found a wide distribution of T(g) as well as a distribution of the thermal expansivity α within the thin films, implying the dynamic heterogeneity of the thin films along the depth direction. The reported anomalous film thickness dependences of T(g) and α were reasonably understood in terms of the distributions, showing that the surface mobile layer and the bottom hard interfacial layer are, respectively, responsible for the depressions of T(g) and α with decreasing film thickness. The molecular mobility in each layer is also discussed in relation to the distribution of T(g), based on the results on mutual diffusion at the layer interface.
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Affiliation(s)
- Rintaro Inoue
- Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan
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9
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Affiliation(s)
- C. M. Roland
- Naval Research Laboratory, Chemistry Division, Code 6120, Washington, D.C. 20375-5342
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Inoue R, Kanaya T, Nishida K, Tsukushi I, Telling MTF, Gabrys BJ, Tyagi M, Soles C, Wu WL. Glass transition and molecular mobility in polymer thin films. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:031802. [PMID: 19905138 DOI: 10.1103/physreve.80.031802] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2009] [Indexed: 05/28/2023]
Abstract
Extensive studies on polymer thin films to date have revealed their interesting but unusual properties such as film thickness dependence of glass transition temperature Tg and thermal expansivity. Recent studies have shown that the lower Tg is not always related to the higher mobility in polymer thin films, which contradicts our current understanding of the glass transition process. In this work, we report the results of inelastic neutron-scattering measurements on polystyrene thin films using two spectrometers with different energy resolutions as well as ellipsometry measurements. The results are interpreted in terms of cooperatively rearranging region and motional slowing down due to the surface effect that explain plausibly the anomalous relationship between the glass transition temperature Tg and the molecular mobility in thin films.
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Affiliation(s)
- R Inoue
- Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan
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