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Patil S, Mbonu C, Chou T, Li R, Wu D, Akcora P, Cheng S. Dynamics of poly(methyl acrylate)/poly(methyl methacrylate)-grafted-Fe 3O 4 nanocomposites. SOFT MATTER 2024; 20:7970-7982. [PMID: 39348039 DOI: 10.1039/d4sm00731j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/01/2024]
Abstract
We investigated the dynamics of nanocomposites prepared through mixing poly(methyl methacrylate) grafted Fe3O4 nanoparticles (PMMA-g-Fe3O4) with poly(methyl acrylate) (PMA). A key feature here different from previous dynamics measurements of polymer nanocomposites is the different chemistry between the matrix polymer and the polymer grafts, which introduces chemical heterogeneity. Transmission electron microscopy shows clear evidence of nanoparticle clustering due to the poor miscibility between the bulk PMA and the bulk PMMA. At the same time, broadband dielectric spectroscopy measurements detect two leading relaxations, i.e. the α and α* processes, where the α process is associated with the bulk PMA and the α* process from the PMA interacting with the grafted PMMA in the nanoparticle clustering region. Interestingly, the characteristic time of α*, τα*, is slightly slower than that of the α, τα, at high temperatures, and exhibits near Arrhenius temperature dependence at low temperatures. As a result, τα* and τα cross each other in the activation plot upon cooling and τα* ≪ τα is observed at temperatures approaching the glass transition temperature of PMA. These observations suggest the presence of component dynamics and the dynamics confinement effect between PMA and PMMA in the nanoparticle clustering region, highlighting an active interaction between PMA and PMMA at the interface despite their poor miscibility. These results thus suggest new routes to control interface dynamics through immiscible polymer pairs.
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Affiliation(s)
- Shalin Patil
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA.
| | - Christopher Mbonu
- Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
| | - Tsengming Chou
- Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
| | - Ruhao Li
- Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
| | - Di Wu
- Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
| | - Pinar Akcora
- Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
| | - Shiwang Cheng
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA.
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2
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Xu J, Ghanekarade A, Li L, Zhu H, Yuan H, Yan J, Simmons DS, Tsui OKC, Wang X. Mixed equilibrium/nonequilibrium effects govern surface mobility in polymer glasses. Proc Natl Acad Sci U S A 2024; 121:e2406262121. [PMID: 39361647 PMCID: PMC11474049 DOI: 10.1073/pnas.2406262121] [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: 03/28/2024] [Accepted: 09/05/2024] [Indexed: 10/05/2024] Open
Abstract
Using angle-resolved X-ray photoelectron spectroscopy, sum-frequency generation vibrational spectroscopy, contact angle measurements, and molecular dynamics simulations, we verify that the glass transition temperature (Tg) of polymer glass is lower near the free surface. However, the experimental Tg-gradients showed a linear variation with depth (z) from the free surface, while the simulated equilibrium Tg-gradients exhibited a double exponential z-dependence. In typical simulations, Tg is determined based on the relaxation time of the system reaching a prescribed threshold value at equilibrium. Conversely, the experiments determined Tg by observing the unfreezing of molecular mobility during heating from a kinetically arrested, nonequilibrium glassy state. To investigate the impact of nonequilibrium effects on the Tg-gradient, we reduced the thermal annealing time in simulations, allowing the system to fall out of equilibrium. We observe a decrease in the relaxation time and the emergence of a modified z-dependence consistent with a linear Tg-gradient near the free surface. We further validate the impact of nonequilibrium effects by studying the dependence of the Tg on the heating/cooling rate for polymer films of varying thickness (h). Our experimental results reveal significant variations in the Tg-heating/cooling rate dependence with h below the bulk Tg, which are also observed in simulation when the simulated system is not equilibrated. We explain our findings by the reduction in mass density within the inner region of the system under nonequilibrium conditions, as observed in simulation, and recent research indicating a decrease in the local Tg of a polymer when placed next to a softer material.
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Affiliation(s)
- Jianquan Xu
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Asieh Ghanekarade
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, FL33620
| | - Li Li
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Huifeng Zhu
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Hailin Yuan
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region999077, China
| | - Jinsong Yan
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region999077, China
| | - David S. Simmons
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, FL33620
| | - Ophelia K. C. Tsui
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region999077, China
- William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Hong Kong Special Administrative Region999077, China
| | - Xinping Wang
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
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3
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Behbahani AF, Harmandaris V. Relaxation dynamics of a liquid in the vicinity of an attractive surface: The process of escaping from the surface. J Chem Phys 2024; 161:134508. [PMID: 39360684 DOI: 10.1063/5.0231689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2024] [Accepted: 09/18/2024] [Indexed: 10/04/2024] Open
Abstract
We analyze the displacements of the particles of a glass-forming molecular liquid perpendicular to a confining solid surface using extensive molecular dynamics simulations with atomistic models. In the vicinity of an attractive surface, the liquid molecules are trapped. Transient localization of liquid molecules near the surface introduces a relaxation process related to the escape of molecules from the surface into the dynamics of the interfacial liquid layer. To describe this process, we analyze several dynamical observables of the confined liquid. The self-intermediate scattering function and the mean-squared displacement of the particles located in the interfacial layer are dominated by the process of escaping from the surface. This relaxation process is also associated with a strong heterogeneity in the mobility of the interfacial particles. The studied model liquid is hydrogenated methyl methacrylate. For the confining wall, we consider different models, namely a periodic single layer of graphene and a frozen amorphous configuration of the bulk liquid (frozen wall). Near graphene, where the liquid molecules form a layered structure and adopt parallel-to-surface orientation, a clear separation between small-scale movements of the molecules near the surface and the process of escaping from the surface is observed. This is reflected in the three-step relaxation of the interfacial layer. However, near the frozen wall, where the liquid molecules do not have a preferential alignment, a clear three-step relaxation is not seen, even though the dynamical quantities are controlled by the process of escaping from the surface.
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Affiliation(s)
- Alireza F Behbahani
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, D-55099 Mainz, Germany
- Institute of Applied and Computational Mathematics, Foundation for Research and Technology-Hellas, Heraklion GR 71110, Greece
| | - Vagelis Harmandaris
- Institute of Applied and Computational Mathematics, Foundation for Research and Technology-Hellas, Heraklion GR 71110, Greece
- Computation-based Science and Technology Research Center, The Cyprus Institute, Nicosia 2121, Cyprus
- Department of Mathematics and Applied Mathematics, University of Crete, Heraklion GR 71110, Greece
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4
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Nakane T, Sasaki T. Thickness-Dependent Segmental Dynamics in Supported Thin Films: Insights from a Dynamically Correlated Network Model. J Phys Chem B 2024; 128:9005-9013. [PMID: 39227037 DOI: 10.1021/acs.jpcb.4c02883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/05/2024]
Abstract
A large body of experimental studies shows that the local dynamics in supercooled liquids are significantly altered by spatial nanoconfinement. In a previous study, we proposed a concept of a dynamically correlated network (DCN) model, which assumes that segments in a supercooled liquid undergo cooperative rearrangements within a network-like cluster. We further demonstrated that a model modified for freestanding thin films can predict for the glass transition dynamics in atactic polystyrene (PS) films consistent with experimental results. In this study, we adapted the model to apply it to supported thin films by introducing a layer of virtual vacant segments at the free surface and virtual anchoring segments at the liquid/substrate interface. The latter segments, carrying a finite number of virtual segments, reduce mobility at the interface. We evaluated the cooperative cluster size and distribution with respect to temperature and film thickness, along with the average relaxation time and glass transition temperature Tg for supported thin films of PS. The model predicted that the thickness dependence of Tg for PS becomes stronger with increasing time scale, and this result agreed well with experimental data across different timescales from pseudothermodynamic and dynamic measurements. The results provide insights into the origin of the dynamical decoupling between pseudothermodynamic and dynamic glass transition behaviors.
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Affiliation(s)
- Tatsuki Nakane
- Department of Materials Science and Engineering, University of Fukui, Fukui 9108507, Japan
| | - Takashi Sasaki
- Department of Materials Science and Engineering, University of Fukui, Fukui 9108507, Japan
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5
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Hefner S, Horstmann R, Kloth S, Vogel M. Quantitative Understanding of Liquid Dynamics at Interfaces from a Free-Energy Landscape Perspective. PHYSICAL REVIEW LETTERS 2024; 133:106201. [PMID: 39303258 DOI: 10.1103/physrevlett.133.106201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Revised: 05/10/2024] [Accepted: 07/24/2024] [Indexed: 09/22/2024]
Abstract
On the basis of molecular dynamics simulations of water and ethanol in nanopores, we devise a methodology to determine the free-energy landscape (FEL) imposed by an interface on an adjoining liquid directly from the particle trajectories. The methodology merely uses the statistical mechanical relation between occupancy and energy and, hence, is particularly suitable in complex situations, e.g., for disordered or rough atomistic interfaces and molecular liquids, as encountered in many biological, geological, and technological situations. Moreover, we show that the thus-obtained FEL enables a quantitative understanding of interface effects on liquid dynamics. Specifically, by determining the local minima and barriers of the FEL and using an Arrhenius-like relation, we reproduce the very strong spatial variation of the structural relaxation time of water and ethanol across nanopores over a broad temperature range. We anticipate that the proposed FEL approach is transferable to various other liquids and interfaces.
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Bothra U, Venugopal H, Kabra D, McNeill CR, Liu ACY. Visualization of Nanocrystallites in Organic Semiconducting Blends Using Cryo-Electron Microscopy. SMALL METHODS 2024; 8:e2301352. [PMID: 38349044 DOI: 10.1002/smtd.202301352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 01/19/2024] [Indexed: 08/18/2024]
Abstract
The efficiency of an organic solar cell is highly dependent on the complex, interpenetrating morphology, and molecular order within the composite phases of the bulk heterojunction (BHJ) blend. Both these microstructural aspects are strongly influenced by the processing conditions and chemical design of donor/acceptor materials. To establish improved structure-function relationships, it is vital to visualize the local microstructural order to provide specific local information about donor/acceptor interfaces and crystalline texture in BHJ blend films. The visualization of nanocrystallites, however, is difficult due to the complex semi-crystalline structure with few characterization techniques capable of visualizing the molecular ordering of soft materials at the nanoscale. Here, it is demonstrated how cryo-electron microscopy can be utilized to visualize local nanoscale order. This method is used to understand the distribution/orientation of crystallites in a BHJ blend. Long-range (>300 nm) texturing of IEICO-4F crystallites oriented in an edge-on fashion is observed, which has not previously been observed for spin-coated materials. This approach provides a wealth of quantitative information about the texture and size of nanocrystallites, which can be utilized to understand charge generation and transport in organic film. This study guides tailoring the material design and processing conditions for high-performance organic optoelectronic devices.
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Affiliation(s)
- Urvashi Bothra
- IITB-Monash Research Academy, IIT Bombay, Powai, Mumbai, 400076, India
- Department of Physics, IIT Bombay, Powai, Mumbai, 400076, India
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800, Australia
| | - Hariprasad Venugopal
- Ramaciotti Centre for Cryo-Electron Microscopy, Monash University, Clayton, Victoria, 3800, Australia
| | - Dinesh Kabra
- Department of Physics, IIT Bombay, Powai, Mumbai, 400076, India
| | - Christopher R McNeill
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800, Australia
| | - Amelia C Y Liu
- School of Physics and Astronomy, Monash University, Clayton, Victoria, 3800, Australia
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Tian H, Luo J, Tang Q, Zha H, Priestley RD, Hu W, Zuo B. Intramolecular dynamic coupling slows surface relaxation of polymer glasses. Nat Commun 2024; 15:6082. [PMID: 39030198 PMCID: PMC11271542 DOI: 10.1038/s41467-024-50398-7] [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: 01/31/2024] [Accepted: 07/09/2024] [Indexed: 07/21/2024] Open
Abstract
Over the past three decades, studies have indicated a mobile surface layer with steep gradients on glass surfaces. Among various glasses, polymers are unique because intramolecular interactions - combined with chain connectivity - can alter surface dynamics, but their fundamental role has remained elusive. By devising polymer surfaces occupied by chain loops of various penetration depths, combined with surface dissipation experiments and Monte Carlo simulations, we demonstrate that the intramolecular dynamic coupling along surface chains causes the sluggish bulk polymers to suppress the fast surface dynamics. Such effect leads to that accelerated segmental relaxation on polymer glass surfaces markedly slows when the surface polymers extend chain loops deeper into the film interior. The surface mobility suppression due to the intramolecular coupling reduces the magnitude of the reduction in glass transition temperature commonly observed in thin films, enabling new opportunities for tailoring polymer properties at interfaces and under confinement and producing glasses with enhanced thermal stability.
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Affiliation(s)
- Houkuan Tian
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
| | - Jintian Luo
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
| | - Qiyun Tang
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing, 211189, China.
| | - Hao Zha
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
| | - Rodney D Priestley
- Department of Chemical and Biological Engineering, Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ, 08544, USA.
| | - Wenbing Hu
- Department of Polymer Science, School of Chemistry and Chemical Engineering, State Key Lab of Coordination Chemistry, Nanjing University, Nanjing, 210023, China
| | - Biao Zuo
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China.
- Zhejiang Provincial Innovation Center of Advanced Textile Technology, Shaoxing, 312000, China.
- Zhejiang Sci-Tech University Shengzhou Innovation Research Institute, Shengzhou, 312400, China.
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8
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Ivancic RJS, Audus DJ. Predicting compatibilized polymer blend toughness. SCIENCE ADVANCES 2024; 10:eadk6165. [PMID: 38896612 PMCID: PMC11186489 DOI: 10.1126/sciadv.adk6165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 05/13/2024] [Indexed: 06/21/2024]
Abstract
Polymer blends can yield superior materials by merging the unique properties of their components. However, these mixtures often phase separate, leading to brittleness. While compatibilizers can toughen these blends, their vast design space makes optimization difficult. Here, we develop a model to predict the toughness of compatibilized glassy polymer mixtures. This theory reveals that compatibilizers increase blend toughness by creating molecular bridges that stitch the interface together. We validate this theory by directly comparing its predictions to extensive molecular dynamics simulations in which we vary polymer incompatibility, chain stiffness, compatibilizer areal density, and blockiness of copolymer compatibilizers. We then parameterize the model using self-consistent field theory and confirm its ability to make predictions for practical applications through comparison with simulations and experiments. These results suggest that the theory can optimize compatibilizer design for industrial glassy polymer blends in silico while providing microscopic insight, allowing for the development of next-generation mixtures.
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Affiliation(s)
- Robert J. S. Ivancic
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Debra J. Audus
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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9
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Ye Z, Zhang H, Riggleman RA. Local dynamics and failure of inhomogeneous polymer networks. SOFT MATTER 2024; 20:4734-4743. [PMID: 38836817 DOI: 10.1039/d4sm00087k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2024]
Abstract
Inhomogeneous crosslinked polymers are powerful platforms for materials design, because they can be synthesized from materials that provide complimentary properties to the resulting gel. For example, a membrane with both glassy and rubbery domains will be mechanically robust while enabling transport. The dynamics, and mechanical and failure properties of rubbery/glassy conetworks are only beginning to be studied, and there is likely to be strong heterogeneities in the dynamics and mechanical response. In this study, we use coarse-grained molecular dynamics simulations to generate microphase separated rubbery/glassy polymer networks with a bicontinuous morphology via in silico crosslinking. We study the effect of phase boundary on the local mobility gradient, and our simulation results reveal an asymmetric shift in the local mobility gradient across the interface that extends deeper into the phase with a lower Tg when the system temperature is between the glass transition temperatures of the two phases. Moreover, by employing a model that allows bond breaking, we examine the microscopic mechanism for failure in these networks as a function of the molecular weight of polymer strands between crosslinks and the number fraction of the glassy domain. Under uniaxial extension, we find that the stress is initially larger in the glassy domain. As the deformation proceeds, the segmental dynamics of the two phases homogenize, and subsequently bond breaking begins.
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Affiliation(s)
- Ziyu Ye
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Han Zhang
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Robert A Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
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10
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Wang Y, Li Z, Niu K, Xia W, Giuntoli A. A Molecular Dynamics Study of Mechanical and Conformational Properties of Conjugated Polymer Thin Films. Macromolecules 2024; 57:5130-5142. [PMID: 38882199 PMCID: PMC11171455 DOI: 10.1021/acs.macromol.4c00232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2024] [Revised: 03/24/2024] [Accepted: 05/10/2024] [Indexed: 06/18/2024]
Abstract
Understanding and predicting the mechanical and conformational properties of conjugated polymer (CP) thin films are a central focus in flexible electronic device research. Employing molecular dynamics simulations with an architecture-transferable chemistry-specific coarse-grained (CG) model of poly(3-alkylthiophene)s (P3ATs), developed by using an energy renormalization approach, we investigate the mechanical and conformational behavior of P3AT thin films during deformation. The density profiles and measures of local mobility identify a softer interfacial layer for all films, the thickness of which does not depend on M w or side-chain length. Remarkably, Young's modulus measured via nanoindentation is more sensitive to M w than for tensile tests, which we attribute to distinct deformation mechanisms. High-M w thin films show increased toughness, whereas longer side-chain lengths of P3AT resulted in lower Young's modulus. Fractures in low-M w thin films occur through chain pullout due to insufficient chain entanglement and crazing in the plastic region. Importantly, stretching promoted both chain alignment and longer conjugation lengths of P3AT, potentially enhancing its electronic properties. For instance, at room temperature, stretching P3HT thin films to 150% increases the conjugated length of P3HT thin films from 2.7 nm to 4.7 nm, aligning with previous experimental findings and all-atom simulation results. Furthermore, high-M w thin films display elevated friction forces due to the chain accumulation on the indenter, with negligible variations in the friction coefficient across all thin film systems. These findings offer valuable insights that enhance our understanding and guide the rational design of CP thin films in flexible electronics.
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Affiliation(s)
- Yang Wang
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG, Groningen, The Netherlands
- School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Zhaofan Li
- Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011, United States
| | - Kangmin Niu
- School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
| | - Wenjie Xia
- Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011, United States
| | - Andrea Giuntoli
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG, Groningen, The Netherlands
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11
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Zhai Q, Gao XY, Lee CS, Ong CY, Yan K, Deng HY, Yang S, Lam CH. Surface mobility gradient and emergent facilitation in glassy films. SOFT MATTER 2024; 20:4389-4394. [PMID: 38757511 DOI: 10.1039/d4sm00221k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2024]
Abstract
Confining glassy polymers into films can substantially modify their local and film-averaged properties. We present a lattice model of film geometry with void-mediated facilitation behaviors but free from any elasticity effect. We analyze the spatially varying viscosity to delineate the transport properties of glassy films. The film mobility measurements reported by Yang et al., Science, 2010, 328, 1676 are successfully reproduced. The flow exhibits a crossover from a simple viscous flow to a surface-dominated regime as the temperature decreases. The propagation of a highly mobile front induced by the free surface is visualized in real space. Our approach provides a microscopic treatment of the observed glassy phenomena.
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Affiliation(s)
- Qiang Zhai
- School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an, Shaanxi, 710049, China.
| | - Xin-Yuan Gao
- Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
| | - Chun-Shing Lee
- School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Chin-Yuan Ong
- School of Physics, Yale University, New Haven, Connecticut, 06520, USA
| | - Ke Yan
- School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China.
| | - Hai-Yao Deng
- School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, CF24 3AA, Wales, UK.
| | - Sen Yang
- School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an, Shaanxi, 710049, China.
| | - Chi-Hang Lam
- Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, China.
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12
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Cheng S, Kogut D, Zheng J, Patil S, Yang F, Lu W. Dynamics of polylactic acid under ultrafine nanoconfinement: The collective interface effect and the spatial gradient. J Chem Phys 2024; 160:114904. [PMID: 38506298 DOI: 10.1063/5.0189762] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Accepted: 02/16/2024] [Indexed: 03/21/2024] Open
Abstract
Polymers under nanoconfinement can exhibit large alterations in dynamics from their bulk values due to an interface effect. However, understanding the interface effect remains a challenge, especially in the ultrafine nanoconfinement region. In this work, we prepare new geometries with ultrafine nanoconfinement ∼10nm through controlled distributions of the crystalline phases and the amorphous phases of a model semi-crystalline polymer, i.e., the polylactic acid. The broadband dielectric spectroscopy measurements show that ultrafine nanoconfinement leads to a large elevation in the glass transition temperature and a strong increment in the polymer fragility index. Moreover, new relaxation time profile analyses demonstrate a spatial gradient that can be well described by either a single-exponential decay or a double-exponential decay functional form near the middle of the film with a collective interface effect. However, the dynamics at the 1-2 nm vicinity of the interface exhibit a power-law decay that is different from the single-exponential decay or double-exponential decay functional forms as predicted by theories. Thus, these results call for further investigations of the interface effect on polymer dynamics, especially for interfaces with perturbed chain packing.
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Affiliation(s)
- Shiwang Cheng
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
| | - David Kogut
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
| | - Juncheng Zheng
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
| | - Shalin Patil
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
| | - Fuming Yang
- Department of Civil and Environmental Engineering, Michigan State University, East Lansing, Michigan 48824, USA
| | - Weiyi Lu
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
- Department of Civil and Environmental Engineering, Michigan State University, East Lansing, Michigan 48824, USA
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13
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Tsujioka T, Yamabayashi K, Kotani K. Surface Glass Transition Temperature Region of Diarylethene Films Determined by Nano-Marangoni Effect. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2306145. [PMID: 37847904 DOI: 10.1002/smll.202306145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 09/28/2023] [Indexed: 10/19/2023]
Abstract
For the last two decades, research has addressed whether the glass transition temperature and the molecular motions on the surface of organic films are significantly different from those inside the bulk glasses. It is reported that the surface of the photochromic diarylethene film prepared by vacuum deposition has fluidity and the vacuum deposition of small amount of rubrene molecules induces surface tension fluctuations, generating dents due to the Marangoni flow in nanoscale. The depth of the dents increases in proportion to these radii for the colorless diarylethene film with a bulk glass transition temperature (Tg) close to room temperature. On the other hand, in the colored diarylethene obtained by UV irradiation to the colorless film, the depth becomes constant at a certain level. The Tg distribution in the depth direction is clarified based on an analysis of the dent depth. By approximating the obtained Tg depth distribution with an exponential function, the outermost surface Tg is about 100 K lower than the bulk Tg in the case of photoisomerized diarylethene.
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Affiliation(s)
- Tsuyoshi Tsujioka
- Division of Math, Sciences, and Information Technology in Education, Osaka Kyoiku University, 4-698-2, Asahigaoka, Kashiwara, Osaka, 582-8582, Japan
| | - Keishi Yamabayashi
- Division of Math, Sciences, and Information Technology in Education, Osaka Kyoiku University, 4-698-2, Asahigaoka, Kashiwara, Osaka, 582-8582, Japan
| | - Kazuma Kotani
- Division of Math, Sciences, and Information Technology in Education, Osaka Kyoiku University, 4-698-2, Asahigaoka, Kashiwara, Osaka, 582-8582, Japan
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14
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Phan AD, Schweizer KS. Effect of the nature of the solid substrate on spatially heterogeneous activated dynamics in glass forming supported films. J Chem Phys 2024; 160:074902. [PMID: 38364012 DOI: 10.1063/5.0188016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2023] [Accepted: 01/10/2024] [Indexed: 02/18/2024] Open
Abstract
We extend the force-level elastically collective nonlinear Langevin equation theory to treat the spatial gradients of the alpha relaxation time and glass transition temperature, and the corresponding film-averaged quantities, to the geometrically asymmetric case of finite thickness supported films with variable fluid-substrate coupling. The latter typically nonuniversally slows down motion near the solid-liquid interface as modeled via modification of the surface dynamic free energy caging constraints that are spatially transferred into the film and which compete with the accelerated relaxation gradient induced by the vapor interface. Quantitative applications to the foundational hard sphere fluid and a polymer melt are presented. The strength of the effective fluid-substrate coupling has very large consequences for the dynamical gradients and film-averaged quantities in a film thickness and thermodynamic state dependent manner. The interference of the dynamical gradients of opposite nature emanating from the vapor and solid interfaces is determined, including the conditions for the disappearance of a bulk-like region in the film center. The relative importance of surface-induced modification of local caging vs the generic truncation of the long range collective elastic component of the activation barrier is studied. The conditions for the accuracy and failure of a simple superposition approximation for dynamical gradients in thin films are also determined. The emergence of near substrate dead layers, large gradient effects on film-averaged response functions, and a weak non-monotonic evolution of dynamic gradients in thick and cold films are briefly discussed. The connection of our theoretical results to simulations and experiments is briefly discussed, as is the extension to treat more complex glass-forming systems under nanoconfinement.
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Affiliation(s)
- Anh D Phan
- Faculty of Materials Science and Engineering, Phenikaa University, Hanoi 12116, Vietnam
- Phenikaa Institute for Advanced Study, Phenikaa University, Hanoi 12116, Vietnam
| | - Kenneth S Schweizer
- Departments of Materials Science, Chemistry, Chemical and Biomolecular Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
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15
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Serna S, Wang T, Torkelson JM. Eliminating the Tg-confinement and fragility-confinement effects in poly(4-methylstyrene) films by incorporation of 3 mol % 2-ethylheyxl acrylate comonomer. J Chem Phys 2024; 160:034903. [PMID: 38235797 DOI: 10.1063/5.0189409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 12/22/2023] [Indexed: 01/19/2024] Open
Abstract
Nanoconfined poly(4-methylstyrene) [P(4-MS)] films exhibit reductions in glass transition temperature (Tg) relative to bulk Tg (Tg,bulk). Ellipsometry reveals that 15-nm-thick P(4-MS) films supported on silicon exhibit Tg - Tg,bulk = - 15 °C. P(4-MS) films also exhibit fragility-confinement effects; fragility decreases ∼60% in going from bulk to a 20-nm-thick film. Previous research found that incorporating 2-6 mol % 2-ethylhexyl acrylate (EHA) comonomer in styrene-based random copolymers eliminates Tg- and fragility-confinement effects in polystyrene. Here, we demonstrate that incorporating 3 mol % EHA in a 4-MS-based random copolymer, 97/3 P(4-MS/EHA), eliminates the Tg- and fragility-confinement effects. The invariance of fragility with nanoconfinement of 97/3 P(4-MS/EHA) films, hypothesized to originate from the interdigitation of ethylhexyl groups, indicates that the presence of EHA prevents the free surface from perturbing chain packing and the cooperative mobility associated with Tg. This method of eliminating confinement effects is advantageous as it relies on the simplest of polymerization methods and neat copolymer only slightly altered in composition from homopolymer. We also investigated whether we could eliminate the Tg-confinement effect with low levels of 2-ethylhexyl methacrylate (EHMA) in 4-MS-based or styrene-based copolymers. Although EHMA is structurally nearly identical to EHA, 4-MS-based and styrene-based copolymers incorporating 4 mol % EHMA exhibit Tg-confinement effects similar to P(4-MS) and polystyrene. These results support the special character of EHA in eliminating confinement effects originating at free surfaces.
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Affiliation(s)
- Sergio Serna
- Department of Chemical and Biological Engineering, Evanston, Illinois 60208, USA
| | - Tong Wang
- Department of Chemical and Biological Engineering, Evanston, Illinois 60208, USA
| | - John M Torkelson
- Department of Chemical and Biological Engineering, Evanston, Illinois 60208, USA
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
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16
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Gagnon YJ, Burton JC, Roth CB. Development of broad modulus profile upon polymer-polymer interface formation between immiscible glassy-rubbery domains. Proc Natl Acad Sci U S A 2024; 121:e2312533120. [PMID: 38147561 PMCID: PMC10769838 DOI: 10.1073/pnas.2312533120] [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: 07/21/2023] [Accepted: 11/01/2023] [Indexed: 12/28/2023] Open
Abstract
Interfaces of glassy materials such as thin films, blends, and composites create strong unidirectional gradients to the local heterogeneous dynamics that can be used to elucidate the length scales and mechanisms associated with the dynamic heterogeneity of glasses. We focus on bilayer films of two different polymers with very different glass transition temperatures ([Formula: see text]) where previous work has demonstrated a long-range (∼200 nm) profile in local [Formula: see text] is established between immiscible glassy and rubbery polymer domains when the polymer-polymer interface is formed to equilibrium. Here, we demonstrate that an equally long-ranged gradient in local modulus [Formula: see text] is established when the polymer-polymer interface ([Formula: see text]5 nm) is formed between domains of glassy polystyrene (PS) and rubbery poly(butadiene) (PB), consistent with previous reports of a broad [Formula: see text] profile in this system. A continuum physics model for the shear wave propagation caused by a quartz crystal microbalance across a PB/PS bilayer film is used to measure the viscoelastic properties of the bilayer during the evolution of the PB/PS interface showing the development of a broad gradient in local modulus [Formula: see text] spanning [Formula: see text]180 nm between the glassy and rubbery domains of PS and PB. We suggest these broad profiles in [Formula: see text] and [Formula: see text] arise from a coupling of the spectrum of vibrational modes across the polymer-polymer interface as a result of acoustic impedance matching of sound waves with [Formula: see text] nm during interface broadening that can then trigger density fluctuations in the neighboring domain.
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Affiliation(s)
| | | | - Connie B. Roth
- Department of Physics, Emory University, Atlanta, GA30322
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17
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Kawaguchi D, Sasahara K, Inutsuka M, Abe T, Yamamoto S, Tanaka K. Absolute local conformation of poly(methyl methacrylate) chains adsorbed on a quartz surface. J Chem Phys 2023; 159:244902. [PMID: 38146829 DOI: 10.1063/5.0184315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Accepted: 11/30/2023] [Indexed: 12/27/2023] Open
Abstract
Polymer chains at a buried interface with an inorganic solid play a critical role in the performance of polymer nanocomposites and adhesives. Sum frequency generation (SFG) vibrational spectroscopy with a sub-nanometer depth resolution provides valuable information regarding the orientation angle of functional groups at interfaces. However, in the case of conventional SFG, since the signal intensity is proportional to the square of the second-order nonlinear optical susceptibility and thereby loses phase information, it cannot be unambiguously determined whether the functional groups face upward or downward. This problem can be solved by phase-sensitive SFG (ps-SFG). We here applied ps-SFG to poly(methyl methacrylate) (PMMA) chains in direct contact with a quartz surface, shedding light on the local conformation of chains adsorbed onto the solid surface. The measurements made it possible to determine the absolute orientation of the ester methyl groups of PMMA, which were oriented toward the quartz interface. Combining ps-SFG with all-atomistic molecular dynamics simulation, the distribution of the local conformation and the driving force are also discussed.
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Affiliation(s)
- Daisuke Kawaguchi
- Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
- Center for Polymer Interface and Molecular Adhesion Science, Kyushu University, Fukuoka 819-0395, Japan
| | - Kazuki Sasahara
- Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
| | - Manabu Inutsuka
- Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
| | - Tatsuki Abe
- Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
| | - Satoru Yamamoto
- Center for Polymer Interface and Molecular Adhesion Science, Kyushu University, Fukuoka 819-0395, Japan
| | - Keiji Tanaka
- Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
- Center for Polymer Interface and Molecular Adhesion Science, Kyushu University, Fukuoka 819-0395, Japan
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18
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Hartley AD, Drayer WF, Ghanekarade A, Simmons DS. Interplay between dynamic heterogeneity and interfacial gradients in a model polymer film. J Chem Phys 2023; 159:204905. [PMID: 38032012 DOI: 10.1063/5.0165650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
Glass-forming liquids exhibit long-lived, spatially correlated dynamical heterogeneity, in which some nm-scale regions in the fluid relax more slowly than others. In the nanoscale vicinity of an interface, glass-formers also exhibit the emergence of massive interfacial gradients in glass transition temperature Tg and relaxation time τ. Both of these forms of heterogeneity have a major impact on material properties. Nevertheless, their interplay has remained poorly understood. Here, we employ molecular dynamics simulations of polymer thin films in the isoconfigurational ensemble in order to probe how bulk dynamic heterogeneity alters and is altered by the large gradient in dynamics at the surface of a glass-forming liquid. Results indicate that the τ spectrum at the surface is broader than in the bulk despite being shifted to shorter times, and yet it is less spatially correlated. This is distinct from the bulk, where the τ distribution becomes broader and more spatially organized as the mean τ increases. We also find that surface gradients in slow dynamics extend further into the film than those in fast dynamics-a result with implications for how distinct properties are perturbed near an interface. None of these features track locally with changes in the heterogeneity of caging scale, emphasizing the local disconnect between these quantities near interfaces. These results are at odds with conceptions of the surface as reflecting simply a higher "rheological temperature" than the bulk, instead pointing to a complex interplay between bulk dynamic heterogeneity and spatially organized dynamical gradients at interfaces in glass-forming liquids.
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Affiliation(s)
- Austin D Hartley
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida 33620, USA
| | - William F Drayer
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida 33620, USA
| | - Asieh Ghanekarade
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida 33620, USA
| | - David S Simmons
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida 33620, USA
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19
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Ghanekarade A, Simmons DS. Glass formation and dynamics of model polymer films with one versus two active interfaces. SOFT MATTER 2023; 19:8413-8422. [PMID: 37877245 DOI: 10.1039/d3sm00719g] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2023]
Abstract
Polymers and other glass-forming liquids can exhibit profound alterations in dynamics in the nanoscale vicinity of interfaces, over a range appreciably exceeding that of typical interfacial thermodynamic gradients. The understanding of these dynamical gradients is particularly complicated in systems with internal or external nanoscale dimensions, where a gradient nucleated at one interface can impinge on a second, potentially distinct, interface. To better understand the interactions that govern system dynamics and glass formation in these cases, here we simulate the baseline case of a glass-forming polymer film, over a wide range of thickness, supported on a dynamically neutral substrate that has little effect on nearby dynamics. We compare these results to our prior simulations of freestanding films. Results indicate that dynamical gradients in our simulated systems, as measured based upon translational relaxation, are simply truncated when they impinge on a secondary surface that is locally dynamically neutral. Altered film behavior can be described almost entirely by gradient effects down to the thinnest films probed, with no evidence for finite-size effects sometimes posited to play a role in these systems. Finally, our simulations predict that linear gradient overlap effects in the presence of symmetric dynamically active interfaces yield a non-monotonic variation of the whole free standing film stretching exponent (relaxation time distribution breadth). The maximum relaxation time distribution breadth in simulation is found at a film thickness of 4-5 times the interfacial gradient range. Observation of this maximum in experiment would provide an important validation that the gradient behavior observed in simulation persists to experimental timescales. If validated, observation of this maximum would potentially also enable determination of the dynamic gradient range from experimental mean-film measurements of film dynamics.
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Affiliation(s)
- Asieh Ghanekarade
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida, USA.
| | - David S Simmons
- Department of Chemical, Biological, and Materials Engineering, The University of South Florida, Tampa, Florida, USA.
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20
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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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21
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Das R, Bhowmik BP, Puthirath AB, Narayanan TN, Karmakar S. Soft pinning: Experimental validation of static correlations in supercooled molecular glass-forming liquids. PNAS NEXUS 2023; 2:pgad277. [PMID: 37680690 PMCID: PMC10482383 DOI: 10.1093/pnasnexus/pgad277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 08/14/2023] [Indexed: 09/09/2023]
Abstract
Enormous enhancement in the viscosity of a liquid near its glass transition is a hallmark of glass transition. Within a class of theoretical frameworks, it is connected to growing many-body static correlations near the transition, often called "amorphous ordering." At the same time, some theories do not invoke the existence of such a static length scale in the problem. Thus, proving the existence and possible estimation of the static length scales of amorphous order in different glass-forming liquids is very important to validate or falsify the predictions of these theories and unravel the true physics of glass formation. Experiments on molecular glass-forming liquids become pivotal in this scenario as the viscosity grows several folds (∼ 10 14 ), and simulations or colloidal glass experiments fail to access these required long-time scales. Here we design an experiment to extract the static length scales in molecular liquids using dilute amounts of another large molecule as a pinning site. Results from dielectric relaxation experiments on supercooled Glycerol with different pinning concentrations of Sorbitol and Glucose, as well as the simulations on a few model glass-forming liquids with pinning sites, indicate the versatility of the proposed method, opening possible new avenues to study the physics of glass transition in other molecular liquids.
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Affiliation(s)
- Rajsekhar Das
- Department of Chemistry, University of Texas at Austin, Austin, TX 78712, USA
- TIFR Center for Interdisciplinary Science, Tata Institute of Fundamental Research, Hyderabad 500046, India
| | - Bhanu Prasad Bhowmik
- TIFR Center for Interdisciplinary Science, Tata Institute of Fundamental Research, Hyderabad 500046, India
- Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Anand B Puthirath
- TIFR Center for Interdisciplinary Science, Tata Institute of Fundamental Research, Hyderabad 500046, India
- Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, TX 77005, USA
| | - Tharangattu N Narayanan
- TIFR Center for Interdisciplinary Science, Tata Institute of Fundamental Research, Hyderabad 500046, India
| | - Smarajit Karmakar
- TIFR Center for Interdisciplinary Science, Tata Institute of Fundamental Research, Hyderabad 500046, India
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22
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Zhang Q, Li W, Qiao K, Han Y. Surface premelting and melting of colloidal glasses. SCIENCE ADVANCES 2023; 9:eadf1101. [PMID: 36930717 PMCID: PMC10022898 DOI: 10.1126/sciadv.adf1101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 02/13/2023] [Indexed: 06/18/2023]
Abstract
The nature of liquid-to-glass transition is a major puzzle in science. A similar challenge exists in glass-to-liquid transition, i.e., glass melting, especially for the poorly investigated surface effects. Here, we assemble colloidal glasses by vapor deposition and melt them by tuning particle attractions. The structural and dynamic parameters saturate at different depths, which define a surface liquid layer and an intermediate glassy layer. The power-law growth of both layers and melting front behaviors at different heating rates are similar to crystal premelting and melting, suggesting that premelting and melting can be generalized to amorphous solids. The measured single-particle kinetics reveal various features and confirm theoretical predictions for glass surface layer.
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Affiliation(s)
- Qi Zhang
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Wei Li
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Kaiyao Qiao
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Yilong Han
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
- Hong Kong University of Science and Technology, Shenzhen Research Institute, Shenzhen 518057, China
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23
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Genix AC, Bocharova V, Carroll B, Dieudonné-George P, Chauveau E, Sokolov AP, Oberdisse J. Influence of the Graft Length on Nanocomposite Structure and Interfacial Dynamics. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:748. [PMID: 36839117 PMCID: PMC9960434 DOI: 10.3390/nano13040748] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 02/10/2023] [Accepted: 02/13/2023] [Indexed: 06/17/2023]
Abstract
Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.
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Affiliation(s)
- Anne-Caroline Genix
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095 Montpellier, France
| | - Vera Bocharova
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Bobby Carroll
- Department of Physics, University of Tennessee, Knoxville, TN 37996, USA
| | | | - Edouard Chauveau
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095 Montpellier, France
| | - Alexei P. Sokolov
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Department of Physics, University of Tennessee, Knoxville, TN 37996, USA
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
| | - Julian Oberdisse
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095 Montpellier, France
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24
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Genix AC, Bocharova V, Carroll B, Dieudonné-George P, Chauveau E, Sokolov AP, Oberdisse J. How Tuning Interfaces Impacts the Dynamics and Structure of Polymer Nanocomposites Simultaneously. ACS APPLIED MATERIALS & INTERFACES 2023; 15:7496-7510. [PMID: 36700938 DOI: 10.1021/acsami.2c18083] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Fundamental understanding of the macroscopic properties of polymer nanocomposites (PNCs) remains difficult due to the complex interplay of microscopic dynamics and structure, namely interfacial layer relaxations and three-dimensional nanoparticle (NP) arrangements. The effect of surface modification by alkyl methoxysilanes at different grafting densities has been studied in PNCs made of poly(2-vinylpyridine) and spherical 20 nm silica NPs. The segmental dynamics has been probed by broadband dielectric spectroscopy and the filler structure by small-angle X-ray scattering and reverse Monte Carlo simulations. By combining the particle configurations with the interfacial layer properties, it is shown how surface modification tunes the attractive polymer-particle interactions: bare NPs slow down the polymer interfacial layer dynamics over a thickness of ca. 5 nm, while grafting screens these interactions. Our analysis of interparticle spacings and segmental dynamics provides unprecedented insights into the effect of surface modification on the main characteristics of PNCs: particle interactions and polymer interfacial layers.
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Affiliation(s)
- Anne-Caroline Genix
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095Montpellier, France
| | - Vera Bocharova
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Bobby Carroll
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | | | - Edouard Chauveau
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095Montpellier, France
| | - Alexei P Sokolov
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996, United States
| | - Julian Oberdisse
- Laboratoire Charles Coulomb (L2C), Université de Montpellier, CNRS, F-34095Montpellier, France
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25
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Merrill JH, Li R, Roth CB. End-Tethered Chains Increase the Local Glass Transition Temperature of Matrix Chains by 45 K Next to Solid Substrates Independent of Chain Length. ACS Macro Lett 2023; 12:1-7. [PMID: 36516977 DOI: 10.1021/acsmacrolett.2c00582] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The local glass transition temperature Tg of pyrene-labeled polystyrene (PS) chains intermixed with end-tethered PS chains grafted to a neutral silica substrate was measured by fluorescence spectroscopy. To isolate the impact of the grafted chains, the films were capped with bulk neat PS layers eliminating competing effects of the free surface. Results demonstrate that end-grafted chains strongly increase the local Tg of matrix chains by ≈45 K relative to bulk Tg, independent of grafted chain molecular weight from Mn = 8.6 to 212 kg/mol and chemical end-group, over a wide range of grafting densities σ = 0.003 to 0.33 chains/nm2 spanning the mushroom-to-brush transition regime. The tens-of-degree increase in local Tg resulting from immobilization of the chain ends by covalent bonding in this athermal system suggests a mechanism that substantially increases the local activation energy required for cooperative rearrangements.
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Affiliation(s)
- James H Merrill
- Department of Physics, Emory University, Atlanta, Georgia30322, United States
| | - Ruoyu Li
- Department of Physics, Emory University, Atlanta, Georgia30322, United States
| | - Connie B Roth
- Department of Physics, Emory University, Atlanta, Georgia30322, United States
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26
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Yan J, Xu J, Weng LT, Wang F, Wang X, Yuan H, Wang T, Tsui OKC. Glass Transition of the Surface Monolayer of Polystyrene Films with Different Film Thicknesses and Supporting Surfaces. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c02013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Jinsong Yan
- Department of Physics, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
| | - Jianquan Xu
- Department of Physics, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Lu-Tao Weng
- Materials Characterization and Preparation Facility (GZ), Advanced Materials Thrust, The Hong Kong University of Science and Technology (Guangzhou), Nansha, Guangzhou511400, Guangdong, China
- Department of Chemical and Biological Engineering, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
| | - Fengliang Wang
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Xinping Wang
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou310018, China
| | - Hailin Yuan
- Department of Physics, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
| | - Tong Wang
- Department of Physics, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
- Department of Materials Science & Engineering, Northwestern University, Evanston, Illinois60208-3120, United States
| | - Ophelia K. C. Tsui
- Department of Physics, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
- William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Kowloon, 999077Hong Kong, China
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27
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Ghanekarade A, Simmons DS. Combined Mixing and Dynamical Origins of Tg Alterations Near Polymer–Polymer Interfaces. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Asieh Ghanekarade
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, Florida33544, United States
| | - David S. Simmons
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, Florida33544, United States
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28
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Sun R, Yang J, Patil S, Liu Y, Zuo X, Lee A, Yang W, Wang Y, Cheng S. Relaxation dynamics of deformed polymer nanocomposites as revealed by small-angle scattering and rheology. SOFT MATTER 2022; 18:8867-8884. [PMID: 36377377 DOI: 10.1039/d2sm00775d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The relaxation dynamics of polystyrene (PS)/silica nanocomposites after a large step deformation are studied by a combination of small-angle scattering techniques and rheology. Small-angle X-ray scattering measurements and rheology show clear signatures of nanoparticle aggregation that enhances the mechanical properties of the polymer nanocomposites (PNCs) in the linear viscoelastic regime and during the initial phase of stress relaxation along with accelerated relaxation dynamics. Small-angle neutron scattering experiments under the zero-average-contrast condition reveal, however, smaller structural anisotropy in the PNCs than that in the neat polymer matrix, as well as accelerated anisotropy relaxation. In addition, the degrees of anisotropy reduction and relaxation dynamics acceleration increase with increasing nanoparticle loading. These results are in sharp contrast to the prevailing viewpoint of enhanced molecular deformation as the main mechanism for the mechanical enhancement in PNCs. Furthermore, the observed acceleration of stress relaxation and reduction in structural anisotropy point to two types of nonlinear effects in the relaxation dynamics of PNCs at large deformation.
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Affiliation(s)
- Ruikun Sun
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA.
| | - Jie Yang
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA.
- College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, P. R. China
| | - Shalin Patil
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA.
| | - Yun Liu
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, USA
| | - Xiaobing Zuo
- X-ray Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Andre Lee
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA.
| | - Wei Yang
- College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, P. R. China
| | - Yangyang Wang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
| | - Shiwang Cheng
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824, USA.
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29
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Peng H, Liu H, Voigtmann T. Nonmonotonic Dynamical Correlations beneath the Surface of Glass-Forming Liquids. PHYSICAL REVIEW LETTERS 2022; 129:215501. [PMID: 36461957 DOI: 10.1103/physrevlett.129.215501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 12/20/2021] [Accepted: 10/27/2022] [Indexed: 06/17/2023]
Abstract
Collective motion over increasing length scales is a signature of the vitrification process of liquids. We demonstrate how distinct static and dynamic length scales govern the dynamics of vitrifying films. In contrast to a monotonically growing static correlation length, the dynamical correlation length that measures the extent of surface-dynamics acceleration into the bulk displays a striking nonmonotonic temperature evolution that is robust also against changes in detailed interatomic interaction. This nonmonotonic change defines a crossover temperature T_{*} that is distinct from the critical temperature T_{c} of mode-coupling theory. We connect this nonmonotonic change to a morphological change of cooperative rearrangement regions of fast particles, and to the point where the decoupling of fast-particle motion from the bulk relaxation is most sensitive to fluctuations. We propose a rigorous definition of this new crossover temperature T_{*} within a recent extension of mode-coupling theory, the stochastic β-relaxation theory.
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Affiliation(s)
- Hailong Peng
- School of Materials Science and Engineering, Central South University, 932 South Lushan Rd, 410083 Changsha, China
| | - Huashan Liu
- School of Materials Science and Engineering, Central South University, 932 South Lushan Rd, 410083 Changsha, China
| | - Thomas Voigtmann
- Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51170 Köln, Germany
- Department of Physics, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany
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30
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Yuan H, Yan J, Gao P, Kumar SK, Tsui OKC. Microscale mobile surface double layer in a glassy polymer. SCIENCE ADVANCES 2022; 8:eabq5295. [PMID: 36351025 PMCID: PMC9645724 DOI: 10.1126/sciadv.abq5295] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 09/21/2022] [Indexed: 06/16/2023]
Abstract
This study examines the origin of the widely different length scales, ht-nanometers to micrometers-that have been observed for the propagation of the near-surface enhanced mobility in glassy polymers. Mechanical relaxations of polystyrene films with thicknesses, h, from 5 nm to 186 μm have been studied. For h < ~1 μm, the films relaxed faster than the bulk and the relaxation time decreased with decreasing h below ~100 nm, consistent with the enhanced dynamics originating from a near-surface nanolayer. For h > ~1 μm, a bulk-like relaxation mode emerged, while the fast mode changed to one that extended over ~1 μm from the free surface. These findings evidence that the mobile surface region is inhomogeneous, comprising a nanoscale outer layer and a slower microscale sublayer that relax by different mechanisms. Consequently, measurements probing the enhanced mobility of different mechanisms may find vastly different ht's as shown by the literature.
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Affiliation(s)
- Hailin Yuan
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
- William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Jinsong Yan
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Ping Gao
- Department of Chemical and Biological Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Sanat K. Kumar
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
| | - Ophelia K. C. Tsui
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
- William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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31
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Wang T, Hu S, Zhang S, Peera A, Reffner J, Torkelson JM. Eliminating the Tg-Confinement Effect in Polystyrene Films: Extraordinary Impact of a 2 mol % 2-Ethylhexyl Acrylate Comonomer. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tong Wang
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois60208, United States
| | - Sumeng Hu
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois60208, United States
| | - Sipei Zhang
- The Dow Chemical Company, 400 Arcola Road, Collegeville, Pennsylvania19426, United States
| | - Asghar Peera
- The Dow Chemical Company, 400 Arcola Road, Collegeville, Pennsylvania19426, United States
| | - John Reffner
- The Dow Chemical Company, 400 Arcola Road, Collegeville, Pennsylvania19426, United States
| | - John M. Torkelson
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois60208, United States
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois60208, United States
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32
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Chowdhury M, Monnier X, Cangialosi D, Priestley RD. Decoupling of Glassy Dynamics from Viscosity in Thin Supported Poly( n-butyl methacrylate) Films. ACS POLYMERS AU 2022; 2:333-340. [PMID: 36267547 PMCID: PMC9576260 DOI: 10.1021/acspolymersau.2c00010] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We utilized fast scanning calorimetry to characterize the glass transition temperature (T g) and intrinsic molecular mobility of low-molecular-weight poly(n-butyl methacrylate) thin films of varying thicknesses. We found that the T g and intrinsic molecular mobility were coupled, showing no film thickness-dependent variation. We further employed a unique noncontact capillary nanoshearing technique to directly probe layer-resolved gradients in the rheological response of these films. We found that layer-resolved shear mobility was enhanced with a reduction in film thickness, whereas the effective viscosity decreased. Our results highlight the importance of polymer-substrate attractive interactions and free surface-promoted enhanced mobility, establishing a competitive nanoconfinement effect in poly(n-butyl methacrylate) thin films. Moreover, the findings indicate a decoupling in the thickness-dependent variation of T g and intrinsic molecular mobility with the mechanical responses (shear mobility and effective viscosity).
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Affiliation(s)
- Mithun Chowdhury
- Lab
of Soft Interfaces, Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India
- Center
for Research in Nanotechnology and Science, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Xavier Monnier
- Centro
de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
- Donostia
International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain
| | - Daniele Cangialosi
- Centro
de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
- Donostia
International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain
| | - Rodney D. Priestley
- Chemical
and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
- Princeton
Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540, United States
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33
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Phan AD. Screening and collective effects in randomly pinned fluids: a new theoretical framework. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:435101. [PMID: 35985315 DOI: 10.1088/1361-648x/ac8b51] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Accepted: 08/19/2022] [Indexed: 06/15/2023]
Abstract
We propose a theoretical framework for the dynamics of bulk isotropic hard-sphere systems in the presence of randomly pinned particles and apply this theory to supercooled water to validate it. Structural relaxation is mainly governed by local and non-local activated process. As the pinned fraction grows, a local caging constraint becomes stronger and the long range collective aspect of relaxation is screened by immobile obstacles. Different responses of the local and cooperative motions results in subtle predictions for how the alpha relaxation time varies with pinning and density. Our theoretical analysis for the relaxation time of water with pinned molecules quantitatively well describe previous simulations. In addition, the thermal dependence of relaxation for unpinned bulk water is also consistent with prior computational and experimental data.
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Affiliation(s)
- Anh D Phan
- Faculty of Materials Science and Engineering, Phenikaa Institute for Advanced Study, Phenikaa University, Hanoi 12116, Vietnam
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34
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Petek ES, Katsumata R. Thickness Dependence of Contact Angles in Multilayered Ultrathin Polymer Films. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01123] [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)
- Evon S. Petek
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Dr, Amherst, Massachusetts 01003, United States
| | - Reika Katsumata
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Dr, Amherst, Massachusetts 01003, United States
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35
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Liu M, Liu H, Peng H. Orientational wetting and dynamical correlations toward glass transition on the surface of imidazolium-based ionic liquids. J Chem Phys 2022; 157:034701. [DOI: 10.1063/5.0099845] [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
Surface induces many fascinating physical phenomena, such as dynamic acceleration, surface anchoring, and orientational wetting, and, thus, is of great interest to study. Here, we report classic molecular dynamics simulations on the free-standing surface of imidazolium-based ionic liquids (ILs) [C4mim][PF6] and [C10mim][PF6]. On [C10mim][PF6] surface, a significant orientational wetting is observed, with the wetting strength showing a diverging tendency. Depth of the wetting was captured from the density and orientational order profile by a static length, which remarkably increases below the temperature Tstat upon cooling down. The dynamical correlation length that measures the distance of surface-dynamics acceleration into the bulk was characterized via the spatial-dependent mobility. The translational correlation exhibits a similar drastic increment at Tstat, while the rotational correlation drastically increases at a lower temperature Trot. We connect these results to the dynamics in bulk liquids, by finding Tstat and Trot that correspond to the onset temperatures where the liquids become cooperative for translational and rotational relaxation, respectively. This signifies the importance of collective dynamics in the bulk on the orientational wetting and surface dynamics in the ILs.
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Affiliation(s)
- Min Liu
- School of Materials Science and Engineering, Central South University, 932 South Lushan Rd., 410083 Changsha, China
| | - Huashan Liu
- School of Materials Science and Engineering, Central South University, 932 South Lushan Rd., 410083 Changsha, China
| | - Hailong Peng
- School of Materials Science and Engineering, Central South University, 932 South Lushan Rd., 410083 Changsha, China
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36
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Li Y, Yu J, Tan X, Yu L. Surface Mobility of Amorphous Indomethacin Containing Moisture and a Surfactant: A Concentration-Temperature Superposition Principle. Mol Pharm 2022; 19:2962-2970. [PMID: 35816108 DOI: 10.1021/acs.molpharmaceut.2c00311] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
An amorphous material can have vastly higher mobility on the surface than in the bulk and, as a result, shows fast surface crystallization. Most amorphous materials contain multiple components, but the effect of composition on surface dynamics remains poorly understood. In this study, the surface mobility of amorphous indomethacin was measured using the method of surface-grating decay in the presence of moisture and the surfactant Tween 20. It is found that both components significantly enhance the surface mobility, and their effects are well described by the principle of concentration-temperature superposition (CTS); that is, the same surface dynamics is observed at the same Tg-normalized temperature T/Tg, where Tg is the composition-dependent glass transition temperature. For doped indomethacin showing CTS, the mechanism of surface evolution for a 1000 nm wavelength surface grating transitions from viscous flow at high temperatures to surface diffusion at low temperatures at 1.04 Tg. For the surfactant-doped system, the Tg used is the value for the surface layer that reflects the surface enrichment of the surfactant (measured by X-ray photoelectron spectroscopy). At a high surfactant concentration (>10% by weight), the surface-grating decay rate in the surface-diffusion regime is limited by the large, slow-diffusing surfactant molecules; in this case, CTS holds only for the viscous-flow regime. The CTS principle allows the prediction of the surface dynamics of multicomponent amorphous materials.
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Affiliation(s)
- Yuhui Li
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Junguang Yu
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Xiao Tan
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Lian Yu
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
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37
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Drayer WF, Simmons DS. Sequence Effects on the Glass Transition of a Model Copolymer System. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00664] [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)
- William F. Drayer
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, Florida 33620, United States
| | - David S. Simmons
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, Florida 33620, United States
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38
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Demydiuk F, Solar M, Meyer H, Benzerara O, Paul W, Baschnagel J. Role of torsional potential in chain conformation, thermodynamics, and glass formation of simulated polybutadiene melts. J Chem Phys 2022; 156:234902. [PMID: 35732513 DOI: 10.1063/5.0094536] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
For polymer chains, the torsional potential is an important intramolecular energy influencing chain flexibility and segmental dynamics. Through molecular dynamics simulations of an atomistic model for melts of cis-trans-1,4-polybutadiene (PBD), we explore the effect of the torsions on conformational properties (bond vector correlations and mean-square internal distances), fundamental thermodynamic quantities (density, compressibility, internal energy, and specific heat), and glass transition temperature Tg. This is achieved by systematically reducing the strength of the torsional potential, starting from the chemically realistic chain (CRC) model with the full potential toward the freely rotating chain (FRC) model without the torsional potential. For the equilibrium liquid, we find that the effect of the torsions on polymer conformations is very weak. Still weaker is the influence on the monomer density ρ and isothermal compressibility κT of the polymer liquid, both of which can be considered as independent of the torsional potential. We show that a van der Waals-like model proposed by Long and Lequeux [Eur. Phys. J. E 4, 371 (2001)] allows us to describe very well the temperature (T) dependence of ρ and κT. We also find that our data obey the linear relation between 1/kBTρκT and 1/T (with the Boltzmann constant kB) that has recently been predicted and verified on the experiment by Mirigian and Schweizer [J. Chem. Phys. 140, 194507 (2014)]. For the equilibrium liquid, simulations result in a specific heat, at constant pressure and at constant volume, which increases on cooling. This T dependence is opposite to the one found experimentally for many polymer liquids, including PBD. We suggest that this difference between simulation and experiment may be attributed to quantum effects due to hydrogen atoms and backbone vibrations, which, by construction, are not included in the classical united-atom model employed here. Finally, we also determine Tg from the density-temperature curve monitored in a finite-rate cooling process. While the influence of the torsional potential on ρ(T) is vanishingly small in the equilibrium liquid, the effect of the torsions on Tg is large. We find that Tg decreases by about 150 K when going from the CRC to the FRC model.
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Affiliation(s)
- F Demydiuk
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - M Solar
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - H Meyer
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - O Benzerara
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
| | - W Paul
- Institut für Physik, Martin Luther Universität, D-06099 Halle, Germany
| | - J Baschnagel
- Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, F-67000 Strasbourg, France
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39
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Affiliation(s)
- Catalin P. Gainaru
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
| | - Alexei P. Sokolov
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States
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40
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Zhang R, Madhavi V, Shaffer TD, Androsch R, Schick C. Cyclic Olefin Copolymers (COC) – Excellent Glass Formers with Low Dynamic Fragility. MACROMOL CHEM PHYS 2022. [DOI: 10.1002/macp.202200065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Rui Zhang
- Institute of Physics and Competence Centre°CALOR University of Rostock Rostock 18051 Germany
- Interdisciplinary Center for Transfer‐oriented Research in Natural Sciences (IWE TFN) Martin Luther University Halle‐Wittenberg Halle/Saale 06099 Germany
| | | | | | - René Androsch
- Interdisciplinary Center for Transfer‐oriented Research in Natural Sciences (IWE TFN) Martin Luther University Halle‐Wittenberg Halle/Saale 06099 Germany
| | - Christoph Schick
- Institute of Physics and Competence Centre°CALOR University of Rostock Rostock 18051 Germany
- Butlerov Institute of Chemistry Kazan Federal University 18 Kremlyovskaya Street Kazan 420008 Russia
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41
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Li Y, Bishop C, Cui K, Schmidt JR, Ediger MD, Yu L. Surface diffusion of a glassy discotic organic semiconductor and the surface mobility gradient of molecular glasses. J Chem Phys 2022; 156:094710. [PMID: 35259874 DOI: 10.1063/5.0079890] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Surface diffusion has been measured in the glass of an organic semiconductor, MTDATA, using the method of surface grating decay. The decay rate was measured as a function of temperature and grating wavelength, and the results indicate that the decay mechanism is viscous flow at high temperatures and surface diffusion at low temperatures. Surface diffusion in MTDATA is enhanced by 4 orders of magnitude relative to bulk diffusion when compared at the glass transition temperature Tg. The result on MTDATA has been analyzed along with the results on other molecular glasses without extensive hydrogen bonds. In total, these systems cover a wide range of molecular geometries from rod-like to quasi-spherical to discotic and their surface diffusion coefficients vary by 9 orders of magnitude. We find that the variation is well explained by the existence of a steep surface mobility gradient and the anchoring of surface molecules at different depths. Quantitative analysis of these results supports a recently proposed double-exponential form for the mobility gradient: log D(T, z) = log Dv(T) + [log D0 - log Dv(T)]exp(-z/ξ), where D(T, z) is the depth-dependent diffusion coefficient, Dv(T) is the bulk diffusion coefficient, D0 ≈ 10-8 m2/s, and ξ ≈ 1.5 nm. Assuming representative bulk diffusion coefficients for these fragile glass formers, the model reproduces the presently known surface diffusion rates within 0.6 decade. Our result provides a general way to predict the surface diffusion rates in molecular glasses.
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Affiliation(s)
- Yuhui Li
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
| | - Camille Bishop
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Kai Cui
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - J R Schmidt
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - M D Ediger
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Lian Yu
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
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42
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McKenzie I, Fujimoto D, Karner VL, Li R, MacFarlane WA, McFadden RML, Morris GD, Pearson MR, Raegen AN, Stachura M, Ticknor JO, Forrest JA. A β-NMR study of the depth, temperature, and molecular-weight dependence of secondary dynamics in polystyrene: Entropy–enthalpy compensation and dynamic gradients near the free surface. J Chem Phys 2022; 156:084903. [DOI: 10.1063/5.0081185] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigated the depth, temperature, and molecular-weight (MW) dependence of the γ-relaxation in polystyrene glasses using implanted 8Li+ and β-detected nuclear magnetic resonance. Measurements were performed on thin films with MW ranging from 1.1 to 641 kg/mol. The temperature dependence of the average 8Li spin–lattice relaxation time [Formula: see text] was measured near the free surface and in the bulk. Spin–lattice relaxation is caused by phenyl ring flips, which involve transitions between local minima over free-energy barriers with enthalpic and entropic contributions. We used transition state theory to model the temperature dependence of the γ-relaxation, and hence [Formula: see text]. There is no clear correlation of the average entropy of activation [Formula: see text] and enthalpy of activation [Formula: see text] with MW, but there is a clear correlation between [Formula: see text] and [Formula: see text], i.e., entropy–enthalpy compensation. This results in the average Gibbs energy of activation, [Formula: see text], being approximately independent of MW. Measurements of the temperature dependence of [Formula: see text] as a function of depth below the free surface indicate the inherent entropic barrier, i.e., the entropy of activation corresponding to [Formula: see text] = 0, has an exponential dependence on the distance from the free surface before reaching the bulk value. This results in [Formula: see text] near the free surface being lower than the bulk. Combining these observations results in a model where the average fluctuation rate of the γ-relaxation has a “double-exponential” depth dependence. This model can explain the depth dependence of [Formula: see text] in polystyrene films. The characteristic length of enhanced dynamics is ∼6 nm and approximately independent of MW near room temperature.
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Affiliation(s)
- Iain McKenzie
- TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
- Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Derek Fujimoto
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Victoria L. Karner
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Ruohong Li
- TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
| | - W. Andrew MacFarlane
- TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Ryan M. L. McFadden
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | | | - Matthew R. Pearson
- Department of Physics, University of Liverpool, Liverpool L69 7ZE, United Kingdom
| | - Adam N. Raegen
- TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | | | - John O. Ticknor
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - James A. Forrest
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
- Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
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Zhou Y, Schweizer KS. Theory for the Elementary Time Scale of Stress Relaxation in Polymer Nanocomposites. ACS Macro Lett 2022; 11:199-204. [PMID: 35574769 DOI: 10.1021/acsmacrolett.1c00732] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We construct a microscopic theory for the elementary time scale of stress relaxation in dense polymer nanocomposites. The key dynamical event is proposed to involve the rearrangement of cohesive segment-nanoparticle (NP) tight bridging complexes via an activated small NP dilational motion, which allows the confined segments to relax. The corresponding activation energy is determined by the NP bridge coordination number and potential of mean force barrier. The activation energy varies nonlinearly with interfacial cohesion strength and NP concentration, and a universal master curve is predicted. The theory is in very good agreement with experiments. The underlying ideas are relevant to a variety of other hybrid macromolecular materials involving hard particles and soft macromolecules.
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Ferron TJ, Thelen JL, Bagchi K, Deng C, Gann E, de Pablo JJ, Ediger MD, Sunday DF, DeLongchamp DM. Characterization of the Interfacial Orientation and Molecular Conformation in a Glass-Forming Organic Semiconductor. ACS APPLIED MATERIALS & INTERFACES 2022; 14:3455-3466. [PMID: 34982543 DOI: 10.1021/acsami.1c19948] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The ability to control structure in molecular glasses has enabled them to play a key role in modern technology; in particular, they are ubiquitous in organic light-emitting diodes. While the interplay between bulk structure and optoelectronic properties has been extensively investigated, few studies have examined molecular orientation near buried interfaces despite its critical role in emergent functionality. Direct, quantitative measurements of buried molecular orientation are inherently challenging, and many methods are insensitive to orientation in amorphous soft matter or lack the necessary spatial resolution. To overcome these challenges, we use polarized resonant soft X-ray reflectivity (p-RSoXR) to measure nanometer-resolved, molecular orientation depth profiles of vapor-deposited thin films of an organic semiconductor Tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Our depth profiling approach characterizes the vertical distribution of molecular orientation and reveals that molecules near the inorganic substrate and free surface have a different, nearly isotropic orientation compared to those of the anisotropic bulk. Comparison of p-RSoXR results with near-edge X-ray absorption fine structure spectroscopy and optical spectroscopies reveals that TCTA molecules away from the interfaces are predominantly planar, which may contribute to their attractive charge transport qualities. Buried interfaces are further investigated in a TCTA bilayer (each layer deposited under separate conditions resulting in different orientations) in which we find a narrow interface between orientationally distinct layers extending across ≈1 nm. Coupling this result with molecular dynamics simulations provides additional insight into the formation of interfacial structure. This study characterizes the local molecular orientation at various types of buried interfaces in vapor-deposited glasses and provides a foundation for future studies to develop critical structure-function relationships.
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Affiliation(s)
- Thomas J Ferron
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Jacob L Thelen
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Kushal Bagchi
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Chuting Deng
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Eliot Gann
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Juan J de Pablo
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - M D Ediger
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Daniel F Sunday
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Dean M DeLongchamp
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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Affiliation(s)
- Guido Raos
- Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Via L. Mancinelli 7, I-20131 Milano, Italy
| | - Bruno Zappone
- Consiglio Nazionale delle Ricerche - Istituto di Nanotecnologia (CNR-Nanotec), Via P. Bucci, 33/C, 87036 Rende (CS), Italy
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Zhang W, Starr FW, Douglas JF. Activation free energy gradient controls interfacial mobility gradient in thin polymer films. J Chem Phys 2021; 155:174901. [PMID: 34742183 DOI: 10.1063/5.0064866] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
We examine the mobility gradient in the interfacial region of substrate-supported polymer films using molecular dynamics simulations and interpret these gradients within the string model of glass-formation. No large gradients in the extent of collective motion exist in these simulated films, and an analysis of the mobility gradient on a layer-by-layer basis indicates that the string model provides a quantitative description of the relaxation time gradient. Consequently, the string model indicates that the interfacial mobility gradient derives mainly from a gradient in the high-temperature activation enthalpy ΔH0 and entropy ΔS0 as a function of depth z, an effect that exists even in the high-temperature Arrhenius relaxation regime far above the glass transition temperature. To gain insight into the interfacial mobility gradient, we examined various material properties suggested previously to influence ΔH0 in condensed materials, including density, potential and cohesive energy density, and a local measure of stiffness or u2(z)-3/2, where u2(z) is the average mean squared particle displacement at a caging time (on the order of a ps). We find that changes in local stiffness best correlate with changes in ΔH0(z) and that ΔS0(z) also contributes significantly to the interfacial mobility gradient, so it must not be neglected.
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Affiliation(s)
- Wengang Zhang
- Materials Science and Engineering Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Francis W Starr
- Department of Physics, Wesleyan University, Middletown, Connecticut 06459, USA
| | - Jack F Douglas
- Materials Science and Engineering Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
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White RP, Lipson JEG. The dynamics of freestanding films: predictions for poly(2-chlorostyrene) based on bulk pressure dependence and thoughtful sample averaging. SOFT MATTER 2021; 17:9755-9764. [PMID: 34647951 DOI: 10.1039/d1sm01175h] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In this paper we model the segmental relaxation in poly(2-chlorostyrene) 18 nm freestanding films, using only data on bulk samples to characterize the system, and predict film relaxation times (τ) as a function of temperature that are in semi-quantitative agreement with film data. The ability to translate bulk characterization into film predictions is a direct result of our previous work connecting the effects of free surfaces in films with those of changing pressure in the bulk. Our approach combines the Locally Correlated Lattice (LCL) equation of state for prediction of free volume values (Vfree) at any given density (ρ), which are then used in the Cooperative Free Volume (CFV) rate model to predict τ(T, Vfree). A key feature of this work is that we calculate the locally averaged density profile as a function of distance from the surface, ρav(z), using the CFV-predicted lengthscale, Lcoop(z), over which rearranging molecular segments cooperate. As we have shown in the past, ρav(z) is significantly broader than the localized profile, ρ(z), which translates into a relaxation profile, τ(z), exhibiting a breadth that mirrors experimental and simulated results. In addition, we discuss the importance of averaging the log of position dependent relaxation times across a film sample (〈log τ(z)〉), as opposed to averaging the relaxation times, themselves, in order to best approximate a whole sample-averaged value that can be directly compared to experiment.
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Affiliation(s)
- Ronald P White
- Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA.
| | - Jane E G Lipson
- Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA.
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Mei B, Zhou Y, Schweizer KS. Experimental Tests of a Theoretically Predicted Noncausal Correlation between Dynamics and Thermodynamics in Glass-forming Polymer Melts. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c01633] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Baicheng Mei
- Department of Materials Science, University of Illinois, Urbana, Illinois 61801, United States
- Material Research Laboratory, University of Illinois, Urbana, Illinois 61801, United States
| | - Yuxing Zhou
- Department of Materials Science, University of Illinois, Urbana, Illinois 61801, United States
- Material Research Laboratory, University of Illinois, Urbana, Illinois 61801, United States
| | - Kenneth S. Schweizer
- Department of Materials Science, University of Illinois, Urbana, Illinois 61801, United States
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States
- Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, United States
- Material Research Laboratory, University of Illinois, Urbana, Illinois 61801, United States
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Mei B, Dell ZE, Schweizer KS. Theory of Transient Localization, Activated Dynamics, and a Macromolecular Glass Transition in Ring Polymer Liquids. ACS Macro Lett 2021; 10:1229-1235. [PMID: 35549053 DOI: 10.1021/acsmacrolett.1c00530] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We construct a segmental scale force level theory for the center-of-mass diffusion constant and corresponding relaxation time for globally compact unconcatenated ring polymer solutions and melts (degree of polymerization N). The approach is based on slowly decaying macromolecular scale intermolecular force dynamic correlations as the origin of their unusual dynamics. Unentangled Rouse, weakly caged, and activated regimes are predicted. The barrier of the activated regime scales linearly with N and as a power law of concentration, which drives a kinetic glass transition on the radius-of-gyration scale. The values of N at the two dynamic crossovers (Rouse to weakly caged, weakly caged to activated) are proportional, with nonuniversality entering mainly via macromolecular volume fraction and dimensionless compressibility. Quantitative comparisons with simulation data reveal good agreement. Aspects of intermediate time dynamics are analyzed, and predictions are made for the conditions required to observe a macromolecular glass transition in the laboratory and on the computer.
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Han Y, Roth CB. Gradient in refractive index reveals denser near free surface region in thin polymer films. J Chem Phys 2021; 155:144901. [PMID: 34654302 DOI: 10.1063/5.0062054] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A gradient in refractive index that is linear in magnitude with depth into the film is used to fit ellipsometric data for thin polymer films of poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(2-vinyl pyridine) (P2VP). We find that the linear gradient model fits provide more physically realistic refractive index values for thin films compared with the commonly used homogeneous Cauchy layer model, addressing recent reports of physically unrealistic density increases. Counter to common expectations of a simple free volume correlation between density and dynamics, we find that the direction of refractive index (density) gradient indicates a higher density near the free surface, which we rationalize based on the observed faster free surface dynamics needed to create vapor deposited stable glasses with optimized denser molecular packings. The magnitude of refractive index gradient is observed to be three times larger for PMMA than for PS films, while P2VP films exhibit a more muted response possibly reflective of a decoupling in free surface and substrate dynamics in systems with strong interfacial interactions.
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Affiliation(s)
- Yixuan Han
- Department of Physics, Emory University, Atlanta, Georgia 30322, USA
| | - Connie B Roth
- Department of Physics, Emory University, Atlanta, Georgia 30322, USA
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