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Zhai Q, Gao XY, Lee CS, Ong CY, Yan K, Deng HY, Yang S, Lam CH. Surface mobility gradient and emergent facilitation in glassy films. SOFT MATTER 2024; 20:4389-4394. [PMID: 38757511 DOI: 10.1039/d4sm00221k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2024]
Abstract
Confining glassy polymers into films can substantially modify their local and film-averaged properties. We present a lattice model of film geometry with void-mediated facilitation behaviors but free from any elasticity effect. We analyze the spatially varying viscosity to delineate the transport properties of glassy films. The film mobility measurements reported by Yang et al., Science, 2010, 328, 1676 are successfully reproduced. The flow exhibits a crossover from a simple viscous flow to a surface-dominated regime as the temperature decreases. The propagation of a highly mobile front induced by the free surface is visualized in real space. Our approach provides a microscopic treatment of the observed glassy phenomena.
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Affiliation(s)
- Qiang Zhai
- School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an, Shaanxi, 710049, China.
| | - Xin-Yuan Gao
- Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
| | - Chun-Shing Lee
- School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China
| | - Chin-Yuan Ong
- School of Physics, Yale University, New Haven, Connecticut, 06520, USA
| | - Ke Yan
- School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China.
| | - Hai-Yao Deng
- School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, CF24 3AA, Wales, UK.
| | - Sen Yang
- School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an, Shaanxi, 710049, China.
| | - Chi-Hang Lam
- Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, China.
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2
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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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3
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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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4
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Jo KI, Oh Y, Sung BJ, Kim TH, Um MS, Choi WJ, Bang J, Yuan G, Satija SK, Koo J. Enhanced Dynamics of Confined Polymers near the Immiscible Polymer-Polymer Interface: Neutron Reflectivity Studies. ACS Macro Lett 2020; 9:210-215. [PMID: 35638684 DOI: 10.1021/acsmacrolett.9b01011] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
For polymer-blend films, local dynamics in confined polymer domains tend to differ from the bulk because of significant contributions from the polymer-polymer interface. Herein, we investigated the diffusion dynamics of entangled polymer thin films confined between different polymers in a direction perpendicular to the surface using neutron reflectivity. We found that a bilayer of poly(methyl methacrylate) (PMMA) and deuterated PMMA (dPMMA) sandwiched between polystyrene (PS) layers exhibited significant increase in mobility near the polymer-polymer interface with decreasing PMMA thickness. This indicates that the contribution of repulsive interactions at the immiscible polymer-polymer interface becomes more significant as the film thickness decreases. We also found that the interfacial roughness between PMMA and PS (28 Å at equilibrium) and soft confinement of PS layers did not significantly affect the change in the diffusion dynamics of the adjacent PMMA. This was evidenced by comparison with the diffusion results of multilayers with a flat interface (8 Å at equilibrium) between PMMA and hard PS by UV cross-linking.
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Affiliation(s)
- Kyoung-Il Jo
- Neutron Science Center, Korea Atomic Energy Research Institute (KAERI), Daejeon 34057, Korea
- Department of Chemical and Biological Engineering, Korea University, Seoul 02841, Korea
| | - Younghoon Oh
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 04107, Korea
| | - Bong June Sung
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 04107, Korea
| | - Tae-Ho Kim
- Department of Organic Materials Engineering, Chungnam National University, Daejeon 34134, Korea
| | - Min Seop Um
- Chemical Materials Solutions Center, Korea Research Institute of Chemical Technology, Daejeon 34114, Korea
| | - Woo Jin Choi
- Chemical Materials Solutions Center, Korea Research Institute of Chemical Technology, Daejeon 34114, Korea
| | - Joona Bang
- Department of Chemical and Biological Engineering, Korea University, Seoul 02841, Korea
| | - Guangcui Yuan
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Sushil K. Satija
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Jaseung Koo
- Department of Organic Materials Engineering, Chungnam National University, Daejeon 34134, Korea
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McKenzie I, Cordoni-Jordan D, Cannon J, Cottrell SP. Dynamics of polystyrene probed by muon spin spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:065102. [PMID: 33325374 DOI: 10.1088/1361-648x/abc4ca] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Muon spin spectroscopic measurements were made on atactic low-molecular-weight (LMW) (1.3 kg mol-1) and high-molecular-weight (HMW) (202 kg mol-1) polystyrene. Muoniated cyclohexadienyl radicals, which are formed by muonium addition to the phenyl side groups, are used as local probes of bulk dynamics. Muon spin relaxation is caused by the secondary γ-relaxation process, which involves motion of the phenyl rings, and is sensitive to the glass transition. The activation energy of the γ-relaxation process in the rubbery state is 0.60(2) eV in the HMW sample and 0.37(3) eV in the LMW sample.
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Affiliation(s)
- Iain McKenzie
- Centre for Molecular and Material Science, TRIUMF, Vancouver, BC V6T 2A3, Canada
- Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
- Department of Physics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | | | - Joseph Cannon
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - Stephen P Cottrell
- ISIS, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
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Liu Y, Sakurai K. Thickness Changes in Temperature-Responsive Poly( N-isopropylacrylamide) Ultrathin Films under Ambient Conditions. ACS OMEGA 2019; 4:12194-12203. [PMID: 31460334 PMCID: PMC6681975 DOI: 10.1021/acsomega.9b01350] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 07/01/2019] [Indexed: 06/10/2023]
Abstract
In this paper, we report detailed experimental observations of unusual changes in the thickness of solid poly(N-isopropylacrylamide) (PNIPAM) ultrathin films, which are well known to have temperature-responsive hydrophilic-hydrophobic switching properties. To date, a number of studies have been carried out on the bulk and the brush forms of PNIPAM in contact with liquid water, as well as in highly humid environments, and, recently, these ultrathin films have been preliminarily shown to exhibit temperature responses even under low-humidity, ambient conditions. In this work, the thicknesses of ultrathin PNIPAM films in a temperature/moisture-controlled sample stage were monitored continuously using multichannel X-ray reflectometry. At room temperature, the sample thickness showed an unexpected increase after thermal treatment at 70 °C for 3 h. In the temperature cycle between 15 and 60 °C, heating and cooling resulted in some clear differences. During cooling, initially, the thickness was almost constant but began to increase when the temperature exceeded 33 °C, which corresponds to the lower critical solution temperature (LCST). This observation indicates that the PNIPAM ultrathin film is sensitive to the small amounts of water contained in the air, even under ambient, low-humidity conditions. On the other hand, during heating run from 15 to 60 °C, the humidity dependence was monotonic, and no specific changes in the PNIPAM films were observed at around the LCST. By studying the humidity dependence, we found that the hydrophilic and hydrophobic states of the PNIPAM ultrathin film exhibit different temperature dependence behaviors. In addition, we found that swelling takes place even under low-moisture conditions. To understand the difference in the thickness changes observed on cooling and heating further, some models considering the effect of the boundary conditions in the polymer ultrathin film system were considered. In the case of the ultrathin film, the hydrophilic/hydrophobic switching property occurred only in the surface layer, which dominated the absorption of water molecules from air. In contrast, the interface layer was time-stable and provided an escape route for water molecules during heating.
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Affiliation(s)
- Yuwei Liu
- University
of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-0006, Japan
- National
Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047, Japan
| | - Kenji Sakurai
- University
of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-0006, Japan
- National
Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047, Japan
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McKenzie I, Chai Y, Cortie DL, Forrest JA, Fujimoto D, Karner VL, Kiefl RF, Levy CDP, MacFarlane WA, McFadden RML, Morris GD, Pearson MR, Zhu S. Direct measurements of the temperature, depth and processing dependence of phenyl ring dynamics in polystyrene thin films by β-detected NMR. SOFT MATTER 2018; 14:7324-7334. [PMID: 29796450 DOI: 10.1039/c8sm00812d] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
There is indirect evidence that the dynamics of a polymer near a free surface are enhanced compared with the bulk but there are few studies of how dynamics varies with depth. β-Detected nuclear spin relaxation of implanted 8Li+ has been used to directly probe the temperature and depth dependence of the γ-relaxation mode, which is due to phenyl rings undergoing restricted rotation, in thin films of atactic deuterated polystyrene (PS-d8) and determine how the depth dependence of dynamics is affected by sample processing, such as annealing, floating on water and the inclusion of a surfactant, and by the presence of a buried interface. The activation energy for the γ-relaxation process is lower near the free surface. Annealing the PS-d8 films and then immersing in water to mimic the floating procedure used to transfer films had negligible effects on the thickness of the region near the free surface with enhanced mobility. Measurements on a bilayer film indicate enhanced phenyl ring dynamics near the buried interface compared with a single film at the same depth. PS-d8 films annealed with the surfactant sodium dodecyl sulfate (SDS) deposited on the surface show enhanced dynamics in the bulk compared with a pure PS-d8 film and a PS-d8 film where the SDS was washed away. There is less contrast between the surface and bulk in the SDS-treated sample, which could account for the elimination of the Tg confinement effect observed in films containing SDS [Chen and Torkelson, Polymer, 2016, 87, 226].
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Zhang W, Douglas JF, Starr FW. Effects of a “bound” substrate layer on the dynamics of supported polymer films. J Chem Phys 2017; 147:044901. [DOI: 10.1063/1.4994064] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Affiliation(s)
- Wengang Zhang
- Department of Physics, Wesleyan University, Middletown, Connecticut 06459-0155, USA
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - Francis W. Starr
- Department of Physics, Wesleyan University, Middletown, Connecticut 06459-0155, USA
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Jin K, Torkelson JM. T g -confinement effects in strongly miscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) and polystyrene: Roles of bulk fragility and chain segregation. POLYMER 2017. [DOI: 10.1016/j.polymer.2017.04.069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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10
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Askar S, Wei T, Tan AW, Torkelson JM. Molecular weight dependence of the intrinsic size effect on T g in AAO template-supported polymer nanorods: A DSC study. J Chem Phys 2017; 146:203323. [PMID: 28571378 DOI: 10.1063/1.4978574] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many studies have established a major effect of nanoscale confinement on the glass transition temperature (Tg) of polystyrene (PS), most commonly in thin films with one or two free surfaces. Here, we characterize smaller yet significant intrinsic size effects (in the absence of free surfaces or significant attractive polymer-substrate interactions) on the Tg and fragility of PS. Melt infiltration of various molecular weights (MWs) of PS into anodic aluminum oxide (AAO) templates is used to create nanorods supported on AAO with rod diameter (d) ranging from 24 to 210 nm. The Tg (both as Tg,onset and fictive temperature) and fragility values are characterized by differential scanning calorimetry. No intrinsic size effect is observed for 30 kg/mol PS in template-supported nanorods with d = 24 nm. However, effects on Tg are present for PS nanorods with Mn and Mw ≥ ∼175 kg/mol, with effects increasing in magnitude with increasing MW. For example, in 24-nm-diameter template-supported nanorods, Tg, rod - Tg, bulk = -2.0 to -2.5 °C for PS with Mn = 175 kg/mol and Mw = 182 kg/mol, and Tg, rod - Tg, bulk = ∼-8 °C for PS with Mn = 929 kg/mol and Mw = 1420 kg/mol. In general, reductions in Tg occur when d ≤ ∼2Rg, where Rg is the bulk polymer radius of gyration. Thus, intrinsic size effects are significant when the rod diameter is smaller than the diameter (2Rg) associated with the spherical volume pervaded by coils in bulk. We hypothesize that the Tg reduction occurs when chain segment packing frustration is sufficiently perturbed by confinement in the nanorods. This explanation is supported by observed reductions in fragility with the increasing extent of confinement. We also explain why these small intrinsic size effects do not contradict reports that the Tg-confinement effect in supported PS films with one free surface exhibits little or no MW dependence.
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Affiliation(s)
- Shadid Askar
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Tong Wei
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - Anthony W Tan
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
| | - John M Torkelson
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, USA
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11
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Jin K, Torkelson JM. Enhanced Tg-Confinement Effect in Cross-Linked Polystyrene Compared to Its Linear Precursor: Roles of Fragility and Chain Architecture. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01042] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Kailong Jin
- Department of Chemical and Biological
Engineering and ‡Department of Materials Science
and Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - John M. Torkelson
- Department of Chemical and Biological
Engineering and ‡Department of Materials Science
and Engineering, Northwestern University, Evanston, Illinois 60208, United States
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12
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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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