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Zorn R, Szymoniak P, Kolmangadi MA, Malpass-Evans R, McKeown NB, Jalarvo NH, Tyagi M, Böhning M, Schönhals A. Microscopic molecular mobility of high-performance polymers of intrinsic microporosity revealed by neutron scattering - bend fluctuations and signature of methyl group rotation. SOFT MATTER 2024; 20:5153-5163. [PMID: 38895763 DOI: 10.1039/d4sm00520a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
Polymers of intrinsic microporosity exhibit a combination of high gas permeability and reasonable permselectivity, which makes them attractive candidates for gas separation membrane materials. The diffusional selective gas transport properties are connected to the molecular mobility of these polymers in the condensed state. Incoherent quasielastic neutron scattering was carried out on two polymers of intrinsic microporosity, PIM-EA-TB(CH3) and its demethylated counterpart PIM-EA-TB(H2), which have high Brunauer-Emmett-Teller surface area values of 1030 m2 g-1 and 836 m2 g-1, respectively. As these two polymers only differ in the presence of two methyl groups at the ethanoanthracene unit, the effect of methyl group rotation can be investigated solely. To cover a broad dynamic range, neutron time-of-flight was combined with neutron backscattering. The demethylated PIM-EA-TB(H2) exhibits a relaxation process with a weak intensity at short times. As the backbone is rigid and stiff this process was assigned to bend-and-flex fluctuations. This process was also observed for the PIM-EA-TB(CH3). A further relaxation process is found for PIM-EA-TB(CH3), which is the methyl group rotation. It was analyzed by a jump-diffusion in a three-fold potential considering also the fact that only a fraction of the present hydrogens in PIM-EA-TB(CH3) participate in the methyl group rotation. This analysis can quantitatively describe the q dependence of the elastic incoherent structure factor. Furthermore, a relaxation time for the methyl group rotation can be extracted. A high activation energy of 35 kJ mol-1 was deduced. This high activation energy evidences a strong hindrance of the methyl group rotation in the bridged PIM-EA-TB(CH3) structure.
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Affiliation(s)
- Reiner Zorn
- Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science (JCNS-1) and Institute for Biological Information Processing (IBI-8), Jülich 52425, Germany
| | - Paulina Szymoniak
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, Berlin 12205, Germany.
| | - Mohamed A Kolmangadi
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, Berlin 12205, Germany.
| | - Richard Malpass-Evans
- EastChem, School of Chemistry, David Brewster Road, University of Edinburgh, Edinburgh, EH9 3FJ, UK
| | - Neil B McKeown
- EastChem, School of Chemistry, David Brewster Road, University of Edinburgh, Edinburgh, EH9 3FJ, UK
| | - Niina H Jalarvo
- Neutron Scattering Division, OAK RIDGE National Laboratory, One Bethel Valley Rd, Oak Ridge, TN 37831, USA
| | - Madhusudan Tyagi
- NIST Center for Neutron Research Gaithersburg MD 20899 and Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | - Martin Böhning
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, Berlin 12205, Germany.
| | - Andreas Schönhals
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, Berlin 12205, Germany.
- Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, Berlin 10623, Germany
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Thoms E, Song Z, Wang K, Napolitano S. Simple Model to Predict the Adsorption Rate of Polymer Melts. PHYSICAL REVIEW LETTERS 2024; 132:248101. [PMID: 38949357 DOI: 10.1103/physrevlett.132.248101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 02/16/2024] [Accepted: 05/16/2024] [Indexed: 07/02/2024]
Abstract
We determine the adsorption rate of polymer melts by means of measurements of molecular mobility. We show that the complex set of molecular rearrangements involved in the adsorption of polymers on flat surfaces can be modeled as an equilibration kinetics driven by the slow Arrhenius process (SAP), a recently discovered molecular mechanism. Our predictive model is based on the single hypothesis that the number of chains adsorbed per unit surface within the timescale of spontaneous fluctuations associated to the SAP is a temperature-invariant constant, not depending on the chemical structure of the polymer. Going beyond the qualitative arguments setting a correlation between equilibrium and nonequilibrium properties, we demonstrate that the rate at which an adsorbed layer grows does not depend on interfacial interactions. By considering simple physical arguments, we demonstrate that this quantity can be straightforwardly determined using the energy barrier of molecular motion as only input.
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Cheng S, Patil S, Cheng S. Hydrogen Bonding Exchange and Supramolecular Dynamics of Monohydroxy Alcohols. PHYSICAL REVIEW LETTERS 2024; 132:058201. [PMID: 38364139 DOI: 10.1103/physrevlett.132.058201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 01/03/2024] [Indexed: 02/18/2024]
Abstract
We unravel hydrogen bonding dynamics and their relationship with supramolecular relaxations of monohydroxy alcohols (MAs) at intermediate times. The rheological modulus of MAs exhibits Rouse scaling relaxation of G(t)∼t^{-1/2} switching to G(t)∼t^{-1} at time τ_{m} before their terminal time. Meanwhile, dielectric spectroscopy reveals clear signatures of new supramolecular dynamics matching with τ_{m} from rheology. Interestingly, the characteristic time τ_{m} follows an Arrhenius-like temperature dependence over exceptionally wide temperatures and agrees well with the hydrogen bonding exchange time from nuclear magnetic resonance measurements. These observations demonstrate the presence of Rouse modes and active chain swapping of MAs at intermediate times. Moreover, detailed theoretical analyses point out explicitly that the hydrogen bonding exchange truncates the Rouse dynamics of the supramolecular chains and triggers the chain-swapping processes, supporting a recently proposed living polymer model.
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Affiliation(s)
- Shinian Cheng
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Shalin Patil
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
| | - Shiwang Cheng
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA
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Teng Y, Guo Y. Multiple relaxation dynamics under electric field enables tunable viscoelastic response of poly(methyl methacrylate) above glass transition temperature. J Chem Phys 2024; 160:044903. [PMID: 38258926 DOI: 10.1063/5.0186755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Accepted: 12/29/2023] [Indexed: 01/24/2024] Open
Abstract
Optimizing mechanical performance is crucial for the practical utilization of stimuli-responsive polymers, while complex viscous and elastic behavior hinders a deep understanding of functional polymers under external field excitation. Here, we demonstrate the in situ dynamic and static mechanical responses under electric stimuli of poly(methyl methacrylate) (PMMA) above glass transition temperature (Tg) by applying a direct current electric field vertically to the mechanical loading. The results show that the electro-mechanical response of PMMA is directly correlated to chain relaxation modes with different length scales: for local segments, polarization provides resistance for molecular motion, manifested by enhanced moduli, increased transient viscosity, and a wider linear viscoelastic range, whereas in a larger spatial range, polarization-induced conformation change causes faster relaxation, reduced elastic modulus, and a lowered modulus plateau. Moreover, flow viscosity is reduced because of weaker friction between chain segments under polarization. Our results suggest effective strategies for precisely tuning the viscoelastic behavior of polymers above Tg through electric stimuli.
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Affiliation(s)
- Yinuo Teng
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yunlong Guo
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
- School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
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Thoms E, Li C, Napolitano S. Tracing the slow Arrhenius process deep in the glassy state-quantitative evaluation of the dielectric relaxation of bulk samples and thin polymer films in the temperature domain. J Chem Phys 2024; 160:034901. [PMID: 38226828 DOI: 10.1063/5.0184382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Accepted: 12/25/2023] [Indexed: 01/17/2024] Open
Abstract
The slow Arrhenius process (SAP) is a dielectric mode connected to thermally activated equilibration mechanisms, allowing for a fast reduction in free energy in liquids and glasses. The SAP, however, is still poorly understood, and so far, this process has mainly been investigated at temperatures above the glass transition. By employing a combination of methods to analyze dielectric measurements under both isochronal and isothermal conditions, we were able to quantitatively reproduce the dielectric response of the SAP of different polymers and to expand the experimental regime over which this process can be observed down to lower temperatures, up to 70 K below the glass transition. Employing thin films of thicknesses varying between 10 and 800 nm, we further verified that the peak shape and activation energy of the SAP of poly(4-bromostyrene) are not sensitive to temperature, nor do they vary upon confinement at the nanoscale level. These observations confirm the preliminary trends reported for other polymers. We find that one single set of parameters-meaning the activation barrier and the pre-exponential factor, respectively, linked to the enthalpic and entropic components of the process-can describe the dynamics of the SAP in both the supercooled liquid and glassy states, in bulk and thin films. These results are discussed in terms of possible molecular origins of the slow Arrhenius process in polymers.
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Affiliation(s)
- Erik Thoms
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université Libre de Bruxelles (ULB), Brussels 1050, Belgium
| | - Chun Li
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université Libre de Bruxelles (ULB), Brussels 1050, Belgium
| | - Simone Napolitano
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université Libre de Bruxelles (ULB), Brussels 1050, Belgium
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Madhusudanan M, Chowdhury M. An entropy generation approach to the molecular recoiling stress relaxation in thin nonequilibrated polymer films. J Chem Phys 2024; 160:014904. [PMID: 38180259 DOI: 10.1063/5.0185728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Accepted: 12/18/2023] [Indexed: 01/06/2024] Open
Abstract
In polymers, the equilibrium state is achieved when the chains have access to the maximum number of conformational states, which allows them to explore a larger conformational space, leading to an increase in the entropy of the system. Preparation of thin polymer films using the spin-coating technique results in polymer chains being locked in a nonequilibrium state with lower entropy due to possible stretching of chains during the process. Allowing enough time for recovery results in the relaxation of the spin-coating-induced molecular recoiling stress. Annealing such a film generates entropy due to its inherent irreversibility. We employed the dewetting technique to determine the molecular recoiling stress relaxation time in poly-(tertbutyl styrene) thin films. Furthermore, we qualitatively differentiated the metastable states achieved by the polymer film using entropy generation in a relaxing polymer film as an effect of thermal entropy and associated it with the conformational entropy of polymer chains utilizing the molecular recoiling stress relaxation time. This enabled us to explain molecular recoiling stress relaxation using a rather simplistic approach involving segmental level molecular rearrangements in polymer chains by attaining transient metastable states through an entropically activated process driving toward equilibrium.
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Affiliation(s)
- Mithun Madhusudanan
- Lab of Soft Interfaces, Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Mithun Chowdhury
- Lab of Soft Interfaces, Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India
- Center for Research in Nano Technology and Science, Indian Institute of Technology Bombay, Mumbai 400076, India
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Caporaletti F, Napolitano S. The slow Arrhenius process in small organic molecules. Phys Chem Chem Phys 2024; 26:745-748. [PMID: 38053485 DOI: 10.1039/d3cp05044k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Equilibration, the complex set of molecular rearrangements leading to more stable states, is usually dominated by density fluctuations, occurring through the structural (α-)relaxation, whose timescale quickly increases upon cooling. Growing evidence shows, however, that equilibration can be reached also through an alternative pathway provided by the Slow Arrhenius process (SAP), a molecular mode slower than the structural processes in the liquid state and faster in glass. The SAP, widely observed in polymers, has not yet been reported in small molecules, probably because of the larger experimental difficulties in handling these systems. Here, we report the presence of the SAP in three different molecular glassformers, by investigating these systems in the thin film geometry via dielectric spectroscopy. These results reinforce the idea that the SAP is a universal feature of liquid and glassy dynamics.
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Affiliation(s)
- Federico Caporaletti
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université libre de Bruxelles (ULB), Brussels 1050, Belgium.
| | - Simone Napolitano
- Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université libre de Bruxelles (ULB), Brussels 1050, Belgium.
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