1
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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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2
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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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3
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Xiao Y, Bai P, Guo Y. Modulus alteration of thin polystyrene films by their neighboring PDMS: Soft and hard confinement. J Chem Phys 2024; 160:211105. [PMID: 38832730 DOI: 10.1063/5.0209251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Accepted: 05/17/2024] [Indexed: 06/05/2024] Open
Abstract
It is highly demanded to understand the confinement effect on nanoconfined polymers. Recent studies reported a strong perturbation of local dynamics and substantial alteration of glass transition temperature Tg at nanoscale. However, how confinement affects the mechanical properties of polymers is not fully understood. Here, we show that the modulus of thin polymer films could be remarkedly altered through a polymer-polymer interface. The modulus of a thin polystyrene (PS) film next to a polydimethylsiloxane (PDMS) was determined from the PS-PDMS bilayer bulging test. A series of experiments show that the modulus of PS can be increased up to 37%, when the modulus of the neighboring PDMS varies from 1.04 to 4.88 MPa. The results demonstrate a strong sensitivity of mechanical properties of thin polymers to the hard/soft environment, which we attribute to the change of high-mobility layer by the polymer-polymer interface.
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Affiliation(s)
- Yuhan Xiao
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Pei Bai
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yunlong Guo
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
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4
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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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5
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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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6
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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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7
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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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8
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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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9
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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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10
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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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11
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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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12
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Phan AD. Confinement Effects on the Spatially Inhomogeneous Dynamics in Metallic Glass Films. J Phys Chem B 2022; 126:1609-1614. [PMID: 35166111 DOI: 10.1021/acs.jpcb.1c08862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This work develops the elastically collective nonlinear Langevin equation theory to investigate, for the first time, the glassy dynamics in capped metallic glass thin films. Finite-size effects on the spatial gradient of structural relaxation time and glass transition temperature (Tg) are calculated at different temperatures and vitrification criteria. Molecular dynamics is significantly slowed down near rough solid surfaces, and the dynamics at location far from the interfaces is sped up. In thick films, the mobility gradient normalized by the bulk value obeys the double-exponential form since interference effects between two surfaces are weak. Reducing the film thickness induces a strong dynamic coupling between two surfaces and flattens the relaxation gradient. The normalized gradient of the glass transition temperature is independent of vitrification time scale criterion and can be fitted by a superposition function as the films are not ultrathin. The local fragility is found to remain unchanged with location. This finding suggests that one can use Angell plots of bulk relaxation time and the Tg spatial gradient to characterize glassy dynamics in metallic glass films. Our computational results agree well with experimental data and simulation.
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Affiliation(s)
- Anh D Phan
- Faculty of Materials Science and Engineering, Computer Science, Artificial Intelligence Laboratory, Phenikaa Institute for Advanced Study, Phenikaa University, Hanoi 12116, Vietnam
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13
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Müller M. Selection of Advances in Theory and Simulation during the First Decade of ACS Macro Letters. ACS Macro Lett 2021; 10:1629-1635. [PMID: 35549151 DOI: 10.1021/acsmacrolett.1c00750] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Marcus Müller
- Institute for Theoretical Physics, Georg-August-University, 37077 Göttingen, Germany
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14
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Ghanekarade A, Phan AD, Schweizer KS, Simmons DS. Nature of dynamic gradients, glass formation, and collective effects in ultrathin freestanding films. Proc Natl Acad Sci U S A 2021; 118:e2104398118. [PMID: 34326262 PMCID: PMC8346796 DOI: 10.1073/pnas.2104398118] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular, polymeric, colloidal, and other classes of liquids can exhibit very large, spatially heterogeneous alterations of their dynamics and glass transition temperature when confined to nanoscale domains. Considerable progress has been made in understanding the related problem of near-interface relaxation and diffusion in thick films. However, the origin of "nanoconfinement effects" on the glassy dynamics of thin films, where gradients from different interfaces interact and genuine collective finite size effects may emerge, remains a longstanding open question. Here, we combine molecular dynamics simulations, probing 5 decades of relaxation, and the Elastically Cooperative Nonlinear Langevin Equation (ECNLE) theory, addressing 14 decades in timescale, to establish a microscopic and mechanistic understanding of the key features of altered dynamics in freestanding films spanning the full range from ultrathin to thick films. Simulations and theory are in qualitative and near-quantitative agreement without use of any adjustable parameters. For films of intermediate thickness, the dynamical behavior is well predicted to leading order using a simple linear superposition of thick-film exponential barrier gradients, including a remarkable suppression and flattening of various dynamical gradients in thin films. However, in sufficiently thin films the superposition approximation breaks down due to the emergence of genuine finite size confinement effects. ECNLE theory extended to treat thin films captures the phenomenology found in simulation, without invocation of any critical-like phenomena, on the basis of interface-nucleated gradients of local caging constraints, combined with interfacial and finite size-induced alterations of the collective elastic component of the structural relaxation process.
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Affiliation(s)
- Asieh Ghanekarade
- Department of Chemical, Biological and Materials Engineering, University of South Florida, Tampa, FL 33620
| | - Anh D Phan
- Faculty of Materials Science and Engineering, Phenikaa University, Hanoi 12116, Vietnam;
| | - Kenneth S Schweizer
- Department of Materials Science, University of Illinois, Urbana, IL 61801;
- Department of Chemistry, University of Illinois, Urbana, IL 61801
- Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, IL 61801
| | - David S Simmons
- Department of Chemical, Biological and Materials Engineering, University of South Florida, Tampa, FL 33620;
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15
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Rahman T, Simmons DS. Near-Substrate Gradients in Chain Relaxation and Viscosity in a Model Low-Molecular Weight Polymer. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02888] [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)
- Tamanna Rahman
- Department of Polymer Engineering, The University of Akron, Akron, Ohio 44325, 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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16
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Mapesa EU, Shahidi N, Kremer F, Doxastakis M, Sangoro J. Interfacial Dynamics in Supported Ultrathin Polymer Films-From the Solid to the Free Interface. J Phys Chem Lett 2021; 12:117-125. [PMID: 33307705 DOI: 10.1021/acs.jpclett.0c03211] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Molecular dynamics in ultrathin layers is investigated using nanostructured electrodes to perform broadband dielectric spectroscopy measurements, and by atomistic molecular dynamics simulations. Using poly(vinyl acetate) as the model system and taking advantage of access to the distribution of relaxation times in an extended temperature range above the glass transition temperature, Tg, we demonstrate that while the mean rates of the segmental relaxation remain bulklike down to 12 nm film thickness, modified molecular mobilities arise in the interfacial zones. Combining results from simulations and experiments, we show unambiguously that both the slow relaxations arising from adsorbed polymer segments and the faster modes attributed to segments in the vicinity of the free interface have non-Arrhenius temperature activation. These interfacial regions span thicknesses of ∼1.5 nm each just above the calorimetric Tg independent of molecular weight and film thickness. These deviations at interfaces are relevant for applications of polymers in adhesion, coatings, and polymer nanocomposites.
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Affiliation(s)
- Emmanuel Urandu Mapesa
- Department of Chemical and Biomolecular Engineering, University of Tennessee Knoxville, 1512 Middle Drive, Knoxville, Tennessee 37996, United States
| | - Nobahar Shahidi
- Department of Chemical and Biomolecular Engineering, University of Tennessee Knoxville, 1512 Middle Drive, Knoxville, Tennessee 37996, United States
| | - Friedrich Kremer
- Department of Molecular Physics, Peter Debye Institute of Soft Matter Physics, University of Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
| | - Manolis Doxastakis
- Department of Chemical and Biomolecular Engineering, University of Tennessee Knoxville, 1512 Middle Drive, Knoxville, Tennessee 37996, United States
| | - Joshua Sangoro
- Department of Chemical and Biomolecular Engineering, University of Tennessee Knoxville, 1512 Middle Drive, Knoxville, Tennessee 37996, United States
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17
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Oda Y, Kawaguchi D, Morimitsu Y, Yamamoto S, Tanaka K. Direct observation of morphological transition for an adsorbed single polymer chain. Sci Rep 2020; 10:20914. [PMID: 33262397 PMCID: PMC7708982 DOI: 10.1038/s41598-020-77761-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 11/06/2020] [Indexed: 11/09/2022] Open
Abstract
A better understanding of the structure of polymers at solid interfaces is crucial for designing various polymer nano-composite materials from structural materials to nanomaterials for use in industry. To this end, the first step is to obtain information on how synthetic polymer chains adsorb onto a solid surface. We closely followed the trajectory of a single polymer chain on the surface as a function of temperature using atomic force microscopy. Combining the results with a full-atomistic molecular dynamics simulation revealed that the chain became more rigid on the way to reaching a pseudo-equilibrium state, accompanied by a change in its local conformation from mainly loops to trains. This information will be useful for regulating the physical properties of polymers at the interface.
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Affiliation(s)
- Yukari Oda
- Department of Applied Chemistry, Kyushu University, Fukuoka, 819-0395, Japan
- Center for Polymer Interface and Molecular Adhesion Science, Kyushu University, Fukuoka, 819-0395, Japan
| | - 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
| | - Yuma Morimitsu
- 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.
- International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka, 819-0395, Japan.
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18
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Gagnon YJ, Roth CB. Local Glass Transition Temperature Tg( z) Within Polystyrene Is Strongly Impacted by the Modulus of the Neighboring PDMS Domain. ACS Macro Lett 2020; 9:1625-1631. [PMID: 35617064 DOI: 10.1021/acsmacrolett.0c00659] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Profiles in the local glass transition temperature Tg(z) within polystyrene (PS) next to polydimethylsiloxane (PDMS) domains were determined using a localized fluorescence method. By changing the base to cross-linker ratio, we varied the cross-link density and, hence, the Young's modulus of PDMS (Sylgard 184). The local Tg(z) in PS at a distance of z = 50 nm away from the PS/PDMS interface was found to shift by 40 K as the PDMS modulus was varied from 0.9 to 2.6 MPa, demonstrating a strong sensitivity of this phenomenon to the rigidity of the neighboring domain. The extent the Tg(z) perturbation persists away from the PS/PDMS interface, z ≈ 65-90 nm before bulk Tg is recovered, is much shorter for this strongly immiscible system compared with the weakly immiscible systems studied previously, which we attribute to a smaller interfacial width, as the χ parameter for PS/PDMS is an order of magnitude larger.
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Affiliation(s)
- Yannic J. Gagnon
- Department of Physics, Emory University, Atlanta, Georgia 30322, United States
| | - Connie B. Roth
- Department of Physics, Emory University, Atlanta, Georgia 30322, United States
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19
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Fujimoto D, MacFarlane WA, Rottler J. Energy barriers and cooperative motion at the surface of freestanding glassy polystyrene films. J Chem Phys 2020; 153:154901. [PMID: 33092352 DOI: 10.1063/5.0022958] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigate the near-surface relaxation of freestanding atactic polystyrene films with molecular dynamics simulations. As in previous coarse-grained simulations, relaxation times for backbone segments and phenyl rings are linked to their bulk relaxation times via a power-law coupling relation. Variation of the coupling exponent with distance from the surface is consistent with depth-dependent activation barriers. We also quantify a reduction in dynamical heterogeneity at the interface, which can be interpreted in the framework of cooperative models for glassy dynamics.
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Affiliation(s)
- D Fujimoto
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - W A MacFarlane
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - J Rottler
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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20
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Wei T, Torkelson JM. Molecular Weight Dependence of the Glass Transition Temperature ( Tg)-Confinement Effect in Well-Dispersed Poly(2-vinyl pyridine)–Silica Nanocomposites: Comparison of Interfacial Layer Tg and Matrix Tg. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01577] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Tong Wei
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - John M. Torkelson
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
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