1
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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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2
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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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3
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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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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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5
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Zhang T, Wang N, Riggleman RA. Failure and Mechanical Properties of Glassy Diblock Copolymer Thin Films. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Tianren Zhang
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania19104, United States
| | - Ning Wang
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana46556, United States
| | - Robert A. Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania19104, United States
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6
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Local conformations and heterogeneities in structures and dynamics of isotactic polypropylene adsorbed onto carbon fiber. POLYMER 2022. [DOI: 10.1016/j.polymer.2022.125584] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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7
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Tannoury L, Solar M, Paul W. Structure and dynamics of a 1,4-polybutadiene melt in an alumina nanopore: A molecular dynamics simulation. J Chem Phys 2022; 157:124901. [DOI: 10.1063/5.0105313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present results of Molecular Dynamics simulations of a chemically realistic model of 1,4-polybutadiene (PBD)confined in a cylindrical alumina nanopore of diameter 10 nm. The simulations are done at three different temperaturesabove the glass transition temperature T g . We investigate the density layering across the nanopore as well as theorientational ordering in the polymer melt, brought about by the confinement, on both the segmental and chain scales.For the chain scale ordering, the magnitude and orientation of the axes of the gyration tensor ellipsoid of single chainsare studied and are found to prefer to align parallel to the pore axis. Even though double bonds near the wall arepreferentially oriented along the pore walls, studying the nematic order parameter indicates that there is no nematicordering at the melt-wall interface. As for the dynamics in the melt, we focus here on the mean-square-displacement ofthe monomers for several layers across the nanopore as well as the movement of the chain center of mass which bothdisplay a slowing down of the dynamics in the layer at the wall. We also show the strong adsorption of the monomersto the pore wall at lower temperatures.
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Affiliation(s)
- Lama Tannoury
- Institute of Physics, Martin Luther University Halle Wittenberg, Germany
| | - Mathieu Solar
- Institut f. Physik, Institut National des Sciences Appliques, France
| | - Wolfgang Paul
- Institut f. Physik, Martin-Luther-Universität Halle-Wittenberg, Germany
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8
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Jaeger TD, Simmons DS. Temperature dependence of aging dynamics in highly non-equilibrium model polymer glasses. J Chem Phys 2022; 156:114504. [DOI: 10.1063/5.0080717] [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
A central feature of the non-equilibrium glassy “state” is its tendency to age toward equilibrium, obeying signatures identified by Kovacs over 50 years ago. The origin of these signatures, their fate far from equilibrium and at high temperatures, and the underlying nature of the glassy “state” far from equilibrium remain unsettled. Here, we simulate physical aging of polymeric glasses, driven much farther from equilibrium and at much higher temperatures than possible in experimental melt-quenched glasses. While these glasses exhibit Kovacs’ signatures of glassy aging at sufficiently low temperatures, these signatures disappear above the onset TA of non-Arrhenius equilibrium dynamics, suggesting that TA demarcates an upper bound to genuinely glassy states. Aging times in glasses after temperature up-jumps are found to obey an Arrhenius law interpolating between equilibrium dynamics at TA and at the start of the temperature up-jump, providing a zero-parameter rule predicting their aging behavior and identifying another unrecognized centrality of TA to aging behavior. This differs qualitatively from behavior of our glasses produced by temperature down-jumps, which exhibit a fractional power law decoupling relation with equilibrium dynamics. While the Tool–Narayanaswamy–Moynihan model can predict the qualitative single-temperature behavior of these systems, we find that it fails to predict the disappearance of Kovacs signatures above TA and the temperature dependence of aging after large temperature up-jumps. These findings highlight a need for new theoretical insights into the aging behavior of glasses at ultra-high fictive temperatures and far from equilibrium.
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Affiliation(s)
- Tamara D. Jaeger
- Department of Polymer Engineering, The University of Akron, Akron, Ohio 44325, USA
| | - David S. Simmons
- Department of Chemical, Biological, and Materials Engineering, University of South Florida, Tampa, Florida 33620, USA
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9
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Zhang T, Riggleman RA. Thickness-Dependent Mechanical Failure in Thin Films of Glassy Polymer Bidisperse Blends. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c01630] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tianren Zhang
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Robert A. Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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10
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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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11
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Arabeche K, Delbreilh L, Baer E. Physical aging of multilayer polymer films—influence of layer thickness on enthalpy relaxation process, effect of confinement. JOURNAL OF POLYMER RESEARCH 2021. [DOI: 10.1007/s10965-021-02809-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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12
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Relaxation behavior of polymer thin films: Effects of free surface, buried interface, and geometrical confinement. Prog Polym Sci 2021. [DOI: 10.1016/j.progpolymsci.2021.101431] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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13
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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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14
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Chatterjee D, Annamareddy A, Ketkaew J, Schroers J, Morgan D, Voyles PM. Fast Surface Dynamics on a Metallic Glass Nanowire. ACS NANO 2021; 15:11309-11316. [PMID: 34152730 DOI: 10.1021/acsnano.1c00500] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The dynamics near the surface of glasses can be much faster than in the bulk. We studied the surface dynamics of a Pt-based metallic glass using electron correlation microscopy with sub-nanometer resolution. Our studies show an ∼20 K suppression of the glass transition temperature at the surface. The enhancement in surface dynamics is suppressed by coating the metallic glass with a thin layer of amorphous carbon. Parallel molecular dynamics simulations on Ni80P20 show a similar temperature suppression of the surface glass transition temperature and that the enhanced surface dynamics are arrested by a capping layer that chemically binds to the glass surface. Mobility in the near-surface region occurs via atomic caging and hopping, with a strong correlation between slow dynamics and high cage-breaking barriers and stringlike cooperative motion. Surface and bulk dynamics collapse together as a function of temperature rescaled by their respective glass transition temperatures.
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Affiliation(s)
- Debaditya Chatterjee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Ajay Annamareddy
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Jittisa Ketkaew
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, United States
| | - Jan Schroers
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, United States
| | - Dane Morgan
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Paul M Voyles
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
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15
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White RP, Lipson JEG. Dynamics across a Free Surface Reflect Interplay between Density and Cooperative Length: Application to Polystyrene. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02742] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ronald P. White
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
| | - Jane E. G. Lipson
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
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16
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Zhang T, Winey KI, Riggleman RA. Conformation and dynamics of ring polymers under symmetric thin film confinement. J Chem Phys 2020; 153:184905. [PMID: 33187402 DOI: 10.1063/5.0024729] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Understanding the structure and dynamics of polymers under confinement has been of widespread interest, and one class of polymers that have received comparatively little attention under confinement is that of ring polymers. The properties of non-concatenated ring polymers can also be important in biological fields because ring polymers have been proven to be a good model to study DNA organization in the cell nucleus. From our previous study, linear polymers in a cylindrically confined polymer melt were found to segregate from each other as a result of the strong correlation hole effect that is enhanced by the confining surfaces. By comparison, our subsequent study of linear polymers in confined thin films at similar levels of confinements found only the onset of segregation. In this study, we use molecular dynamics simulation to investigate the chain conformations and dynamics of ring polymers under planar (1D) confinement as a function of film thickness. Our results show that conformations of ring polymers are similar to the linear polymers under planar confinement, except that ring polymers are less compressed in the direction normal to the walls. While we find that the correlation hole effect is enhanced under confinement, it is not as pronounced as the linear polymers under 2D confinement. Finally, we show that chain dynamics far above Tg are primarily affected by the friction from walls based on the monomeric friction coefficient we get from the Rouse mode analysis.
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Affiliation(s)
- Tianren Zhang
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Karen I Winey
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Robert A Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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17
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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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18
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Ivancic RJS, Riggleman RA. Dynamic phase transitions in freestanding polymer thin films. Proc Natl Acad Sci U S A 2020; 117:25407-25413. [PMID: 33008880 PMCID: PMC7568329 DOI: 10.1073/pnas.2006703117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
After more than two decades of study, many fundamental questions remain unanswered about the dynamics of glass-forming materials confined to thin films. Experiments and simulations indicate that free interfaces enhance dynamics over length scales larger than molecular sizes, and this effect strengthens at lower temperatures. The nature of the influence of interfaces, however, remains a point of significant debate. In this work, we explore the properties of the nonequilibrium phase transition in dynamics that occurs in trajectory space between high- and low-mobility basins in a set of model polymer freestanding films. In thick films, the film-averaged mobility transition is broader than the bulk mobility transition, while in thin films it is a variant of the bulk result shifted toward a higher bias. Plotting this transition's local coexistence points against the distance from the films' surface shows thick films have surface and film-center transitions, while thin films practically have a single transition throughout the film. These observations are reminiscent of thermodynamic capillary condensation of a vapor-liquid phase between parallel plates, suggesting they constitute a demonstration of such an effect in a trajectory phase transition in the dynamics of a structural glass former. Moreover, this transition bears similarities to several experiments exhibiting anomalous behavior in the glass transition upon reducing film thickness below a material-dependent onset, including the broadening of the glass transition and the homogenization of surface and bulk glass transition temperatures.
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Affiliation(s)
- Robert J S Ivancic
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104
| | - Robert A Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA, 19104
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19
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Diaz Vela D, Ghanekarade A, Simmons DS. Probing the Metrology and Chemistry Dependences of the Onset Condition of Strong “Nanoconfinement” Effects on Dynamics. Macromolecules 2020. [DOI: 10.1021/acs.macromol.9b02693] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Daniel Diaz Vela
- Department of Chemical and Biomedical Engineering, The University of South Florida, Tampa, Florida 33620, United States
| | - Asieh Ghanekarade
- Department of Chemical and Biomedical Engineering, The University of South Florida, Tampa, Florida 33620, United States
| | - David S. Simmons
- Department of Chemical and Biomedical Engineering, The University of South Florida, Tampa, Florida 33620, United States
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20
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Schweizer KS, Simmons DS. Progress towards a phenomenological picture and theoretical understanding of glassy dynamics and vitrification near interfaces and under nanoconfinement. J Chem Phys 2019; 151:240901. [PMID: 31893888 DOI: 10.1063/1.5129405] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The nature of alterations to dynamics and vitrification in the nanoscale vicinity of interfaces-commonly referred to as "nanoconfinement" effects on the glass transition-has been an open question for a quarter century. We first analyze experimental and simulation results over the last decade to construct an overall phenomenological picture. Key features include the following: after a metrology- and chemistry-dependent onset, near-interface relaxation times obey a fractional power law decoupling relation with bulk relaxation; relaxation times vary in a double-exponential manner with distance from the interface, with an intrinsic dynamical length scale appearing to saturate at low temperatures; the activation barrier and vitrification temperature Tg approach bulk behavior in a spatially exponential manner; and all these behaviors depend quantitatively on the nature of the interface. We demonstrate that the thickness dependence of film-averaged Tg for individual systems provides a poor basis for discrimination between different theories, and thus we assess their merits based on the above dynamical gradient properties. Entropy-based theories appear to exhibit significant inconsistencies with the phenomenology. Diverse free-volume-motivated theories vary in their agreement with observations, with approaches invoking cooperative motion exhibiting the most promise. The elastically cooperative nonlinear Langevin equation theory appears to capture the largest portion of the phenomenology, although important aspects remain to be addressed. A full theoretical understanding requires improved confrontation with simulations and experiments that probe spatially heterogeneous dynamics within the accessible 1-ps to 1-year time window, minimal use of adjustable parameters, and recognition of the rich quantitative dependence on chemistry and interface.
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Affiliation(s)
- Kenneth S Schweizer
- Departments of Materials Science, Chemistry and Chemical & Biomolecular Engineering, Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - David S Simmons
- Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, Florida 33620, USA
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22
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Zhang W, Starr FW, Douglas JF. Collective Motion in the Interfacial and Interior Regions of Supported Polymer Films and Its Relation to Relaxation. J Phys Chem B 2019; 123:5935-5941. [PMID: 31192601 PMCID: PMC7430234 DOI: 10.1021/acs.jpcb.9b04155] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To understand the role of collective motion in the often large changes in interfacial molecular mobility observed in polymer films, we investigate the extent of collective motion in the interfacial regions of a thin supported polymer film and within the film interior by molecular dynamics simulation. Contrary to commonly stated expectations, we find that the extent of collective motion, as quantified by string-like molecular exchange motion, is similar in magnitude in the polymer-air interfacial layer as the film interior and distinct from the bulk material. This finding is consistent with Adam-Gibbs description of the segmental dynamics within mesoscopic film regions, where the extent of collective motion is related to the configurational entropy of the film as a whole rather than a locally defined extent of collective motion or configurational entropy.
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Affiliation(s)
- Wengang Zhang
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
- Department of Physics, Wesleyan University, Middletown, Connecticut 06459-0155, United States
| | - Francis W. Starr
- Department of Physics, Wesleyan University, Middletown, Connecticut 06459-0155, United States
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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23
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Phan AD, Schweizer KS. Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b00754] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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24
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Samanta S, Huang G, Gao G, Zhang Y, Zhang A, Wolf S, Woods CN, Jin Y, Walsh PJ, Fakhraai Z. Exploring the Importance of Surface Diffusion in Stability of Vapor-Deposited Organic Glasses. J Phys Chem B 2019; 123:4108-4117. [PMID: 30998844 DOI: 10.1021/acs.jpcb.9b01012] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Stable glasses are formed during physical vapor deposition (PVD), through the surface-mediated equilibration process. Understanding surface relaxation dynamics is important in understanding the details of this process. Direct measurements of the surface relaxation times in molecular glass systems are challenging. As such, surface diffusion measurements have been used in the past as a proxy for the surface relaxation process. In this study, we show that the absence of enhanced surface diffusion is not a reliable predictor of reduced ability to produce stable glasses. To demonstrate, we have prepared stable glasses (SGs) from two structurally similar organic molecules, 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (TNB) and 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene (α,α-A), with similar density increase and improved kinetic stability as compared to their liquid-quenched (LQ) counterparts. The surface diffusion values of these glasses were measured both in the LQ and SG states below their glass transition temperatures ( Tgs) using gold nanorod probes. While TNB shows enhanced surface diffusion in both SG and LQ states, no significant surface Tg diffusion is observed on the surface of α,α-A within our experimental time scales. However, isothermal dewetting experiments on ultrathin films of both molecules below Tg indicate the existence of enhanced dynamics in ultrathin films for both molecules, indirectly showing the existence of an enhanced mobile surface layer. Both films produce stable glasses, which is another indication for the existence of the mobile surface layer. Our results suggest that lateral surface diffusion may not be a good proxy for enhanced surface relaxation dynamics required to produce stable glasses, and thus, other types of measurements to directly probe the surface relaxation times may be necessary.
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Affiliation(s)
- Subarna Samanta
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Georgia Huang
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Gui Gao
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Yue Zhang
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Aixi Zhang
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Sarah Wolf
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Connor N Woods
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Yi Jin
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Patrick J Walsh
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Zahra Fakhraai
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
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25
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Thees MF, Roth CB. Unexpected Molecular Weight Dependence to the Physical Aging of Thin Polystyrene Films Present at Ultra‐High Molecular Weights. ACTA ACUST UNITED AC 2019. [DOI: 10.1002/polb.24797] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | - Connie B. Roth
- Department of Physics Emory University Atlanta Georgia 30322
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26
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Zhang T, Winey KI, Riggleman RA. Polymer Conformations and Dynamics under Confinement with Two Length Scales. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01779] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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27
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Pressly JF, Riggleman RA, Winey KI. Polymer Diffusion Is Fastest at Intermediate Levels of Cylindrical Confinement. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b01728] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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28
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Zhang Y, Woods CN, Alvarez M, Jin Y, Riggleman RA, Fakhraai Z. Effect of substrate interactions on the glass transition and length-scale of correlated dynamics in ultra-thin molecular glass films. J Chem Phys 2018; 149:184902. [PMID: 30441931 DOI: 10.1063/1.5038174] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Interfacial interactions can play an important role in the glass transition temperature (T g ) and relaxation dynamics of ultra-thin glass polymer films. We have recently shown that similar to the polymeric systems in ultra-thin molecular glass films of N, N'-Bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD), the T g is reduced and dynamics are enhanced. Furthermore, in molecular glass systems, as the film thickness is reduced below ∼30 nm, the dynamics at the two interfaces correlate such that the range of the gradients in the dynamics induced by the free surface narrows compared to thicker films. These observations indicate that the dynamics of the glassy thin films are strongly correlated and cannot be explained by a simple two-layer model consisting of a bulk and a thin interfacial layer with a constant thickness and constant range of dynamical gradients. Here, we investigate the effect of film/substrate interactions on the film dynamics by varying the TPD/substrate interfacial interactions. We show that thin TPD films with thicknesses below ∼60 nm show a smaller extent of T g reduction and enhanced dynamics when supported on a near-neutral substrate (wetting) compared to a weakly interacting (dewetting) substrate. However, the ∼30 nm length scale, where the activation energy significantly reduces from its bulk value as measured by the onset of the glass transition remains unchanged. Coarse-grained molecular dynamics simulation also shows a narrowing in the range of relaxation times once the thickness is sufficiently reduced for the two interfaces to dynamically correlate, consistent with previous work. These results suggest that the length-scale for the correlated dynamics is independent of interfacial interactions and the polymeric nature of the film and may originate from the bulk glass properties.
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Affiliation(s)
- Yue Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Connor N Woods
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Mauricio Alvarez
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Yi Jin
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Robert A Riggleman
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6315, USA
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
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29
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Monnier X, Fernandes Nassar S, Domenek S, Guinault A, Sollogoub C, Dargent E, Delpouve N. Reduced physical aging rates of polylactide in polystyrene/polylactide multilayer films from fast scanning calorimetry. POLYMER 2018. [DOI: 10.1016/j.polymer.2018.07.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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30
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Glor EC, Angrand GV, Fakhraai Z. Exploring the broadening and the existence of two glass transitions due to competing interfacial effects in thin, supported polymer films. J Chem Phys 2018; 146:203330. [PMID: 28571332 DOI: 10.1063/1.4979944] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this report, we use ellipsometry to characterize the glass transition in ultra-thin films of poly(2-vinyl pyridine) (P2VP) supported on a silicon substrate. P2VP is known to have attractive substrate interactions, which can increase the Tg of ultra-thin films compared to the bulk value. Here, we use an extended temperature range to show that the glass transition can be extremely broad, indicating that a large gradient of the dynamics exists through the film with slow dynamics near the substrate and enhanced dynamics at the free surface. To observe the effect of these two interfaces on the average thin film dynamics, cooling rate-dependent Tg (CR-Tg) measurements were used to indirectly probe the average relaxation times of the films. We demonstrate that ultra-thin films have lower fragility compared to bulk films, and, when cooled at slow cooling rates (<1 K/min), exhibit extreme broadening of the dynamics (<70 nm) and eventually complete decoupling between the free surface and substrate regions to produce films with two distinct Tg's (<16 nm). Tg,high increases with decreasing thickness in a similar manner to what has been observed in previous studies on P2VP, and Tg,low decreases with decreasing film thickness in a similar manner to what has been observed in polymer films with enhanced free surfaces and neutral substrate interactions. These observations indicate that the dynamics in thin films of P2VP can be strongly coupled over a length scale of ∼10-20 nm, resulting in two co-existing layers with two distinct glass transitions when the range of the dynamical gradients become too large to sustain (breadth of the transition > 50 K).
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Affiliation(s)
- Ethan C Glor
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Gabriel V Angrand
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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31
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Chakraborty K, Vijayan K, Brown AEX, Discher DE, Loverde SM. Glassy worm-like micelles in solvent and shear mediated shape transitions. SOFT MATTER 2018; 14:4194-4203. [PMID: 29744515 PMCID: PMC6174325 DOI: 10.1039/c8sm00080h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The glassiness of polymer melts is generally considered to be suppressed by small dimensions, added solvent, and heat. Here, we suggest that glassiness persists at the nanoscale in worm-like micelles composed of amphiphilic diblock copolymers of poly(ethylene oxide)-polystyrene (PS). The glassiness of these worms is indicated by a lack of fluorescence recovery after photobleaching as well as micron-length rigid segments separated by hinges. The coarse-grained molecular dynamics studies probe the dynamics of the PS in these glassy worms. Addition of an organic solvent promotes a transition from hinged to fully flexible worms and to spheres or vesicles. Simulation demonstrates two populations of organic solvent in the core of the micelle-a solvent 'pool' in the micelle core and a second population that accumulates at the interface between the core and the corona. The stable heterogeneity of the residual solvent could explain the unusual hinged rigidity, but solvent removal during shear-extension could be more effective and yield - as observed - nearly straight worms without hinges.
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Affiliation(s)
- Kaushik Chakraborty
- Department of Chemistry, College of Staten Island, The City University of New York, 2800 Victory Boulevard, Staten Island, New York 10314, USA.
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32
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Kasavan BL, Baglay RR, Roth CB. Local Glass Transition Temperature
T
g
(
z
) Profile in Polystyrene next to Polybutadiene with and without Plasticization Effects. MACROMOL CHEM PHYS 2017. [DOI: 10.1002/macp.201700328] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | | | - Connie B. Roth
- Department of Physics Emory University Atlanta GA 30322 USA
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33
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Sussman DM, Schoenholz SS, Cubuk ED, Liu AJ. Disconnecting structure and dynamics in glassy thin films. Proc Natl Acad Sci U S A 2017; 114:10601-10605. [PMID: 28928147 PMCID: PMC5635874 DOI: 10.1073/pnas.1703927114] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nanometrically thin glassy films depart strikingly from the behavior of their bulk counterparts. We investigate whether the dynamical differences between a bulk and thin film polymeric glass former can be understood by differences in local microscopic structure. Machine learning methods have shown that local structure can serve as the foundation for successful, predictive models of particle rearrangement dynamics in bulk systems. By contrast, in thin glassy films, we find that particles at the center of the film and those near the surface are structurally indistinguishable despite exhibiting very different dynamics. Next, we show that structure-independent processes, already present in bulk systems and demonstrably different from simple facilitated dynamics, are crucial for understanding glassy dynamics in thin films. Our analysis suggests a picture of glassy dynamics in which two dynamical processes coexist, with relative strengths that depend on the distance from an interface. One of these processes depends on local structure and is unchanged throughout most of the film, while the other is purely Arrhenius, does not depend on local structure, and is strongly enhanced near the free surface of a film.
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Affiliation(s)
| | | | - Ekin D Cubuk
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94304
| | - Andrea J Liu
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104
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34
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Liu T, Exarhos AL, Alguire EC, Gao F, Salami-Ranjbaran E, Cheng K, Jia T, Subotnik JE, Walsh PJ, Kikkawa JM, Fakhraai Z. Birefringent Stable Glass with Predominantly Isotropic Molecular Orientation. PHYSICAL REVIEW LETTERS 2017; 119:095502. [PMID: 28949582 DOI: 10.1103/physrevlett.119.095502] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Indexed: 06/07/2023]
Abstract
Birefringence in stable glasses produced by physical vapor deposition often implies molecular alignment similar to liquid crystals. As such, it remains unclear whether these glasses share the same energy landscape as liquid-quenched glasses that have been aged for millions of years. Here, we produce stable glasses of 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene molecules that retain three-dimensional shapes and do not preferentially align in a specific direction. Using a combination of angle- and polarization-dependent photoluminescence and ellipsometry experiments, we show that these stable glasses possess a predominantly isotropic molecular orientation while being optically birefringent. The intrinsic birefringence strongly correlates with increased density, showing that molecular ordering is not required to produce stable glasses or optical birefringence, and provides important insights into the process of stable glass formation via surface-mediated equilibration. To our knowledge, such novel amorphous packing has never been reported in the past.
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Affiliation(s)
- Tianyi Liu
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Annemarie L Exarhos
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Ethan C Alguire
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Feng Gao
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | | | - Kevin Cheng
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Tiezheng Jia
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Joseph E Subotnik
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Patrick J Walsh
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - James M Kikkawa
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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35
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Zhou Y, Milner ST. Short-Time Dynamics Reveals Tg Suppression in Simulated Polystyrene Thin Films. Macromolecules 2017. [DOI: 10.1021/acs.macromol.7b00921] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Yuxing Zhou
- Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Scott T. Milner
- Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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36
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Tanis I, Meyer H, Salez T, Raphaël E, Maggs AC, Baschnagel J. Molecular dynamics simulation of the capillary leveling of viscoelastic polymer films. J Chem Phys 2017; 146:203327. [PMID: 28571341 DOI: 10.1063/1.4978938] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Surface tension-driven flow techniques have recently emerged as an efficient means of shedding light into the rheology of thin polymer films. Motivated by experimental and theoretical approaches in films bearing a varying surface topography, we present results on the capillary relaxation of a square pattern at the free surface of a viscoelastic polymer film, using molecular dynamics simulations of a coarse-grained polymer model. Height profiles are monitored as a function of time after heating the system above its glass-transition temperature and their time dependence is fitted to the theory of capillary leveling. Results show that the viscosity is not constant, but time dependent. In addition to providing a complementary insight about the local inner mechanisms, our simulations of the capillary-leveling process therefore probe the viscoelasticity of the polymer and not only its viscosity, in contrast to most experimental approaches.
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Affiliation(s)
- I Tanis
- Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, 75005 Paris, France
| | - H Meyer
- Université de Strasbourg, CNRS, Institut Charles Sadron, UPR 22, 67000 Strasbourg, France
| | - T Salez
- Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, 75005 Paris, France
| | - E Raphaël
- Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, 75005 Paris, France
| | - A C Maggs
- Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, 75005 Paris, France
| | - J Baschnagel
- Université de Strasbourg, CNRS, Institut Charles Sadron, UPR 22, 67000 Strasbourg, France
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37
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Tylinski M, Beasley MS, Chua YZ, Schick C, Ediger MD. Limited surface mobility inhibits stable glass formation for 2-ethyl-1-hexanol. J Chem Phys 2017; 146:203317. [DOI: 10.1063/1.4977787] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- M. Tylinski
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
| | - M. S. Beasley
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
| | - Y. Z. Chua
- Institute of Physics, University of Rostock, Albert-Einstein-Str. 23-24, 18051 Rostock, Germany and Competence Centre CALOR, Faculty of Interdisciplinary Research, University of Rostock, Albert-Einstein-Str. 25, 18051 Rostock, Germany
| | - C. Schick
- Institute of Physics, University of Rostock, Albert-Einstein-Str. 23-24, 18051 Rostock, Germany and Competence Centre CALOR, Faculty of Interdisciplinary Research, University of Rostock, Albert-Einstein-Str. 25, 18051 Rostock, Germany
| | - M. D. Ediger
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
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38
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Baglay RR, Roth CB. Local glass transition temperatureTg(z) of polystyrene next to different polymers: Hard vs. soft confinement. J Chem Phys 2017; 146:203307. [DOI: 10.1063/1.4975168] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Affiliation(s)
- Roman R. Baglay
- 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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39
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Napolitano S, Glynos E, Tito NB. Glass transition of polymers in bulk, confined geometries, and near interfaces. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:036602. [PMID: 28134134 DOI: 10.1088/1361-6633/aa5284] [Citation(s) in RCA: 247] [Impact Index Per Article: 35.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at a constant rate, the structural relaxation time of the liquid eventually exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass-a solid lacking long-range order. Despite almost 100 years of research on the (liquid/)glass transition, it is not yet clear which molecular mechanisms are responsible for the unique slow-down in molecular dynamics. In this review, we first introduce the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification. We then analyse the impact of connectivity, structure, and chain environment on molecular motion at the length scale of a few monomers, as well as how macromolecular architecture affects the glass transition of non-linear polymers. We then discuss a revised picture of nanoconfinement, going beyond a simple picture based on interfacial interactions and surface/volume ratio. Analysis of a large body of experimental evidence, results from molecular simulations, and predictions from theory supports, instead, a more complex framework where other parameters are relevant. We focus discussion specifically on local order, free volume, irreversible chain adsorption, the Debye-Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature. We end by highlighting the molecular origin of distributions in relaxation times and glass transition temperatures which exceed, by far, the size of a chain. Fast relaxation modes, almost universally present at the free surface between polymer and air, are also remarked upon. These modes relax at rates far larger than those characteristic of glassy dynamics in bulk. We speculate on how these may be a signature of unique relaxation processes occurring in confined or heterogeneous polymeric systems.
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Affiliation(s)
- Simone Napolitano
- Laboratory of Polymer and Soft Matter Dynamics, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, 1050 Brussels, Belgium
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40
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Wei W, Feng S, Zhou Q, Liang H, Long Y, Wu Q, Gao H, Liang G, Zhu F. Study on glass transition and physical aging of polystyrene nanowires by differential scanning calorimetry. JOURNAL OF POLYMER RESEARCH 2017. [DOI: 10.1007/s10965-017-1199-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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41
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Huang X, Roth CB. Changes in the temperature-dependent specific volume of supported polystyrene films with film thickness. J Chem Phys 2017; 144:234903. [PMID: 27334190 DOI: 10.1063/1.4953855] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Recent studies have measured or predicted thickness-dependent shifts in density or specific volume of polymer films as a possible means of understanding changes in the glass transition temperature Tg(h) with decreasing film thickness with some experimental works claiming unrealistically large (25%-30%) increases in film density with decreasing thickness. Here we use ellipsometry to measure the temperature-dependent index of refraction of polystyrene (PS) films supported on silicon and investigate the validity of the commonly used Lorentz-Lorenz equation for inferring changes in density or specific volume from very thin films. We find that the density (specific volume) of these supported PS films does not vary by more than ±0.4% of the bulk value for film thicknesses above 30 nm, and that the small variations we do observe are uncorrelated with any free volume explanation for the Tg(h) decrease exhibited by these films. We conclude that the derivation of the Lorentz-Lorenz equation becomes invalid for very thin films as the film thickness approaches ∼20 nm, and that reports of large density changes greater than ±1% of bulk for films thinner than this likely suffer from breakdown in the validity of this equation or in the difficulties associated with accurately measuring the index of refraction of such thin films. For larger film thicknesses, we do observed small variations in the effective specific volume of the films of 0.4 ± 0.2%, outside of our experimental error. These shifts occur simultaneously in both the liquid and glassy regimes uniformly together starting at film thicknesses less than ∼120 nm but appear to be uncorrelated with Tg(h) decreases; possible causes for these variations are discussed.
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Affiliation(s)
- Xinru Huang
- 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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42
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Taamalli S, Hinds J, Migirditch S, Teboul V. Enhanced diffusion in finite-size simulations of a fragile diatomic glass former. Phys Rev E 2016; 94:052604. [PMID: 27967093 DOI: 10.1103/physreve.94.052604] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Indexed: 11/07/2022]
Abstract
Using molecular dynamics simulations we investigate the finite-size dependence of the dynamical properties of a diatomic supercooled liquid. The simplicity of the molecule permits us to access the microsecond time scale. We find that the relaxation time decreases simultaneously with the strength of cooperative motions when the size of the system decreases. While the decrease of the cooperative motions is in agreement with previous studies, the decrease of the relaxation time opposes what has been reported to date in monatomic glass formers and in silica. This result suggests the presence of different competing physical mechanisms in the relaxation process. For very small box sizes the relaxation times behavior reverses itself and increases strongly when the box size decreases, thus leading to a nonmonotonic behavior. This result is in qualitative agreement with defect and facilitation theories.
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Affiliation(s)
- Sonia Taamalli
- Laboratoire de Photonique d'Angers EA 4464, University of Angers, Physics Department, 2 Bd Lavoisier, 49045 Angers, France.,University of Monastir, Physics Department, Monastir, Tunisia
| | - Julia Hinds
- Laboratoire de Photonique d'Angers EA 4464, University of Angers, Physics Department, 2 Bd Lavoisier, 49045 Angers, France.,Appalachian State University, Physics department, Boone, North Carolina, USA
| | - Samuel Migirditch
- Laboratoire de Photonique d'Angers EA 4464, University of Angers, Physics Department, 2 Bd Lavoisier, 49045 Angers, France.,Appalachian State University, Physics department, Boone, North Carolina, USA
| | - Victor Teboul
- Laboratoire de Photonique d'Angers EA 4464, University of Angers, Physics Department, 2 Bd Lavoisier, 49045 Angers, France
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43
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Zhang Y, Potter R, Zhang W, Fakhraai Z. Using tobacco mosaic virus to probe enhanced surface diffusion of molecular glasses. SOFT MATTER 2016; 12:9115-9120. [PMID: 27759140 DOI: 10.1039/c6sm01566b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Recent studies have shown that diffusion on the surface of organic glasses can be many orders of magnitude faster than bulk diffusion. Developing new probes that can readily measure surface diffusion can help study the effect of parameters such as chemical structure, intermolecular interaction, molecules' shape and size on the enhanced surface diffusion. In this study, we develop a novel probe that significantly simplifies these types of studies. Tobacco mosaic virus (TMV) is used as probe particle to measure surface diffusion coefficient of molecular glass N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD). The evolution of the meniscus formed around TMV is probed as a function of time at various temperatures. TMV has a well-defined, mono-dispersed, cylindrical shape, with a large aspect-ratio (average diameter of 16.6 nm, length of 300 nm). As such, the shape of the meniscus around the center of TMV is semi-two dimensional, which compared to using a nanosphere as probe, increases the driving force for meniscus formation and simplifies the analysis of surface diffusion. We show that under these conditions, after a short transient time the shape of the meniscus is self-similar, allowing accurate determination of the surface diffusion coefficient. Measurements at various temperatures are then performed to investigate the temperature dependence of the surface diffusion coefficient. It is found that surface diffusion is greatly enhanced in TPD and has a lower activation barrier compared to the bulk counterpart. These observations are consistent with previous studies of surface diffusion on molecular glasses, demonstrating the accuracy of this method.
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Affiliation(s)
- Yue Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
| | - Richard Potter
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
| | - William Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
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44
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Zhang Y, Glor EC, Li M, Liu T, Wahid K, Zhang W, Riggleman RA, Fakhraai Z. Long-range correlated dynamics in ultra-thin molecular glass films. J Chem Phys 2016. [DOI: 10.1063/1.4962734] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yue Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Ethan C. Glor
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Mu Li
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272, USA
| | - Tianyi Liu
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Kareem Wahid
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - William Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Robert A. Riggleman
- Department of Chemical and Bimolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6315, USA
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
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45
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Merling WL, Mileski JB, Douglas JF, Simmons DS. The Glass Transition of a Single Macromolecule. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01461] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Weston L. Merling
- Department
of Polymer Engineering, The University of Akron, 250 South Forge
St., Akron, Ohio 44325-0301, United States
| | - Johnathon B. Mileski
- Department
of Polymer Engineering, The University of Akron, 250 South Forge
St., Akron, Ohio 44325-0301, United States
| | - Jack F. Douglas
- Materials
Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - David S. Simmons
- Department
of Polymer Engineering, The University of Akron, 250 South Forge
St., Akron, Ohio 44325-0301, United States
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46
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Lan T, Torkelson JM. Fragility-Confinement Effects: Apparent Universality as a Function of Scaled Thickness in Films of Freely Deposited, Linear Polymer and Its Absence in Densely Grafted Brushes. Macromolecules 2016. [DOI: 10.1021/acs.macromol.5b02489] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tian Lan
- Department of Materials Science
and Engineering and ‡Department of Chemical and Biological
Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - John M. Torkelson
- Department of Materials Science
and Engineering and ‡Department of Chemical and Biological
Engineering, Northwestern University, Evanston, Illinois 60208, United States
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47
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Affiliation(s)
- David S. Simmons
- Department of Polymer Engineering; University of Akron; 250 South Forge St Akron OH 44325 USA
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48
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Shavit A, Riggleman RA. The dynamics of unentangled polymers during capillary rise infiltration into a nanoparticle packing. SOFT MATTER 2015; 11:8285-8295. [PMID: 26355281 DOI: 10.1039/c5sm01866h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Although highly packed polymer nanocomposites (PNCs) are important for a wide array of applications, preparing them remains difficult because of the poor dispersion of NPs at high loading fractions. One method to successfully prepare PNCs with high loadings is through capillary rise infiltration, as previously shown by Huang et al., although the mechanism of polymer infiltration remains largely unknown. We use molecular dynamics simulations to directly simulate the process of capillary rise infiltration, and we show that the polymers follow Lucas-Washburn dynamics. We observe a wetting front that precedes bulk infiltration, and chains belonging to this front are highly adsorbed to NPs. We also investigate the viscosity of the model polymers both globally and locally in supported and free-standing films, and we find reduced viscosity near the surface of the films and increased viscosity near the supporting substrate, similar to the results of local relaxation times. The reduction in the viscosity at the free surface for short, oligomeric polymers is smaller than for higher molecular weight polymers, and the ratio of the surface viscosities is most consistent with the predictions of the Lucas-Washburn equation. Our results introduce the mechanism by which polymers infiltrate a highly packed NP film, which may shed light on better ways to prepare these materials for energy storage applications and protective coatings.
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Affiliation(s)
- Amit Shavit
- 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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49
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Baglay RR, Roth CB. Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a Tg difference of 80 K. J Chem Phys 2015; 143:111101. [DOI: 10.1063/1.4931403] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Roman R. Baglay
- 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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50
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Glor EC, Composto RJ, Fakhraai Z. Glass Transition Dynamics and Fragility of Ultrathin Miscible Polymer Blend Films. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00979] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ethan C. Glor
- Department of Chemistry and ‡Department of
Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Russell J. Composto
- Department of Chemistry and ‡Department of
Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Zahra Fakhraai
- Department of Chemistry and ‡Department of
Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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