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Stanković I, Dašić M, Jovanović M, Martini A. Effects of Water Content on the Transport and Thermodynamic Properties of Phosphonium Ionic Liquids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:9049-9058. [PMID: 38641549 DOI: 10.1021/acs.langmuir.4c00372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/21/2024]
Abstract
We present a numerical investigation of the influence of water content on the dynamic properties of a family of phosphonium-based room-temperature ionic liquids. The study presents a compelling correlation between structural changes in water-ionic liquid solutions and thermodynamic and transport properties across diverse systems. The results for phosphonium ionic liquids are compared with 1-butyl-3-methylimidazolium hexaphosphate ([bmim]PF6) as a reference. Through this approach, phosphonium cation structure-related characteristics can be identified and placed within the broader context of ionic liquids. These insights are underpinned by observed changes in interaction energy, boiling point, diffusion rate, and viscosity, highlighting the crucial role of water molecules in weakening the strength of interactions between ions within the ionic liquid. The investigation also explains temperature-dependent trends in phosphonium cations, showing that alkyl group length and molecular symmetry are important tuning parameters for the strength of Coulomb interactions. These results contribute to a refined understanding of phosphonium ionic liquid behavior in the presence of water, offering valuable insights for optimizing their use in diverse fields.
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Affiliation(s)
- Igor Stanković
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Miljan Dašić
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Mateja Jovanović
- Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, Belgrade 11080, Serbia
| | - Ashlie Martini
- Department of Mechanical Engineering, University of California, Merced, California 95343, United States
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2
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Dorenbos G. How fork-length asymmetry affects solvent connectivity and diffusion in grafted polymeric model membranes. J Chem Phys 2024; 160:064901. [PMID: 38341779 DOI: 10.1063/5.0193120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 01/15/2024] [Indexed: 02/13/2024] Open
Abstract
The hydrophilic pore morphology and solvent diffusion within model (amphiphilic) polymer membranes are simulated by dissipative particle dynamics (DPD). The polymers are composed of a backbone of 18 covalently bonded A beads to which at regular intervals side chains are attached. The side chains are composed of linear Ap chains (i.e., -A1-A2…Ap) from which two branches, [AsC] and [ArC], split off (s ≤ r). C beads serve as functionalized hydrophilic pendent sites. The branch lengths (s + 1 and r + 1) are varied. Five repeat unit designs (with general formula A3[Ap[AsC][ArC]]) are considered: A2[A3C][A3C] (symmetric branching), A2[A2C][A4C], A2[AC][A5C], A2[C][A6C] (highly asymmetric branching), and A4[AC][A3C]. The distribution of water (W) and W diffusion through nanophase segregated hydrophilic pores is studied. For similar primary length p, an increase in side chain symmetry favors hydrophilic pore connectivity and long-range water transport. C beads located on the longer [ArC] branches reveal the highest C bead mobility and are more strongly associated with water than the C beads on the shorter [AsC] branches. The connectivity of hydrophilic (W and W + C) phases through mapped replica of selected snapshots obtained from Monte Carlo tracer diffusion simulations is in line with trends found from the W bead diffusivities during DPD simulations. The diffusive pathways for protons (H+) in proton exchange membranes and for hydronium (OH-) in anion exchange membranes are the same as for solvents. Therefore, control of the side chain architecture is an interesting design parameter for optimizing membrane conductivities.
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Affiliation(s)
- G Dorenbos
- Private research, Sano 1107-2, Belle Crea 502, 410-1118 Susono, Japan
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3
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Stine JM, Ruland KL, Beardslee LA, Levy JA, Abianeh H, Botasini S, Pasricha PJ, Ghodssi R. Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H 2 S in the Gastrointestinal Tract. Adv Healthc Mater 2024; 13:e2302897. [PMID: 38035728 DOI: 10.1002/adhm.202302897] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 11/20/2023] [Indexed: 12/02/2023]
Abstract
Hydrogen sulfide (H2 S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H2 S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H2 S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H2 S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H2 S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H2 S concentration ranging from 0.21 to 4.5 ppm (R2 = 0.954) with a normalized sensitivity of 12.4% ppm-1 when evaluated in a benchtop setting. The sensor proves highly selective toward H2 S in the presence of known interferent gases, such as hydrogen (H2 ), with a selectivity ratio of H2 S:H2 = 1340, as well as toward methane (CH4 ) and carbon dioxide (CO2 ). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H2 S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H2 S.
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Affiliation(s)
- Justin M Stine
- Department of Electrical and Computer Engineering, University of Maryland, College Park, MD, 20742, USA
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
- Fischell Institute for Biomedical Devices, University of Maryland, College Park, MD, 20742, USA
| | - Katie L Ruland
- Department of Electrical and Computer Engineering, University of Maryland, College Park, MD, 20742, USA
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
- Fischell Institute for Biomedical Devices, University of Maryland, College Park, MD, 20742, USA
| | - Luke A Beardslee
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
| | - Joshua A Levy
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
- Fischell Institute for Biomedical Devices, University of Maryland, College Park, MD, 20742, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA
| | - Hossein Abianeh
- Department of Electrical and Computer Engineering, University of Maryland, College Park, MD, 20742, USA
| | - Santiago Botasini
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
| | - Pankaj J Pasricha
- Department of Internal Medicine, Mayo Clinic Hospital, Phoenix, AZ, 85054, USA
| | - Reza Ghodssi
- Department of Electrical and Computer Engineering, University of Maryland, College Park, MD, 20742, USA
- Institute for Systems Research, University of Maryland, College Park, MD, 20742, USA
- Fischell Institute for Biomedical Devices, University of Maryland, College Park, MD, 20742, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA
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4
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Hemmasi E, Tohidian M, Makki H. Morphology and Transport Study of Acid-Base Blend Proton Exchange Membranes by Molecular Simulations: Case of Chitosan/Nafion. J Phys Chem B 2023; 127:10624-10635. [PMID: 38037344 PMCID: PMC10726362 DOI: 10.1021/acs.jpcb.3c05332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 10/28/2023] [Accepted: 11/20/2023] [Indexed: 12/02/2023]
Abstract
Blending a basic polymer (e.g., chitosan) with Nafion can modify some membrane properties in direct methanol fuel cell applications, e.g., controlling methanol crossover, by regulating the morphology of hydrophilic channels. Unraveling the mechanisms by which the channel morphology is modified is essential to formulate design strategies for acid-base blend membrane development. Thus, we use molecular simulations to analyze the morphological features of a blend membrane (at 75/25 chitosan/Nafion wt %), i.e., (i) water/polymer phase organizations, (ii) number and size of water clusters, and (iii) quantitative morphological measures of hydrophilic channels, and compare them to the pure Nafion in a wide range of water contents. It is found that the affinity of water to different hydrophilic groups in the blend membrane can result in more distorted and dispersed hydrophilic phase and fewer bulk water-like features compared to pure Nafion. Also, the width of the hydrophilic network bottleneck, i.e., pore limiting diameter (PLD), is found to be almost five times smaller for the blend membrane compared to Nafion at their maximum water contents. Moreover, by changing the chitosan/Nafion weight ratio from 75/25 to 0/100, we show that as Nafion content increases, all channel morphological characteristics alter monotonically except PLD. This is mainly due to the strong acid-base interactions between Nafion and chitosan, which hinder the monotonic growth of PLD. Interestingly, water and methanol diffusion coefficients are strongly correlated with PLD, suggesting that PLD can be used as a single parameter for tailoring the blending ratio for achieving the desired diffusion properties of acid-base membranes.
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Affiliation(s)
- Ehsan Hemmasi
- Department
of Polymer and Color Engineering, Amirkabir
University of Technology, 424 Hafez Avenue, Tehran 59163-4311, Iran
| | - Mahdi Tohidian
- Department
of Polymer and Color Engineering, Amirkabir
University of Technology, 424 Hafez Avenue, Tehran 59163-4311, Iran
| | - Hesam Makki
- Department
of Chemistry and Materials Innovation Factory, University of Liverpool, Liverpool L69 7ZD, U.K.
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5
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Wickramasinghe S, Hoehn A, Wetthasinghe ST, Lin H, Wang Q, Jakowski J, Rassolov V, Tang C, Garashchuk S. Theoretical Examination of the Hydroxide Transport in Cobaltocenium-Containing Polyelectrolytes. J Phys Chem B 2023; 127:10129-10141. [PMID: 37972315 DOI: 10.1021/acs.jpcb.3c04118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
Polymers incorporating cobaltocenium groups have received attention as promising components of anion-exchange membranes (AEMs), exhibiting a good balance of chemical stability and high ionic conductivity. In this work, we analyze the hydroxide diffusion in the presence of cobaltocenium cations in an aqueous environment based on the molecular dynamics of model systems confined in one dimension to mimic the AEM channels. In order to describe the proton hopping mechanism, the forces are obtained from the electronic structure computed at the density-functional tight-binding level. We find that the hydroxide diffusion depends on the channel size, modulation of the electrostatic interactions by the solvation shell, and its rearrangement ability. Hydroxide diffusion proceeds via both the vehicular and structural diffusion mechanisms with the latter playing a larger role at low diffusion coefficients. The highest diffusion coefficient is observed under moderate water densities (around half the density of liquid water) when there are enough water molecules to form the solvation shell, reducing the electrostatic interaction between ions, yet there is enough space for the water rearrangements during the proton hopping. The effects of cobaltocenium separation, orientation, chemical modifications, and the role of nuclear quantum effects are also discussed.
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Affiliation(s)
- Sachith Wickramasinghe
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Alexandria Hoehn
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Shehani T Wetthasinghe
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Huina Lin
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Qi Wang
- Department of Mathematics, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Jacek Jakowski
- Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
| | - Vitaly Rassolov
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Chuanbing Tang
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Sophya Garashchuk
- Department of Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
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6
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Dorenbos G. Simulated and Experimental Trends Regarding Water Uptake in Polymeric Electrolyte Membranes. J Phys Chem B 2023; 127:9630-9641. [PMID: 37882051 DOI: 10.1021/acs.jpcb.3c05309] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2023]
Abstract
Polymeric membranes in an anion or a proton exchange membrane fuel cell need sufficient hydration in order to provide a high hydroxide ion or proton conductivity. The water uptake for six model ionomer membranes, all of the same ion exchange capacity, is modeled by dissipative particle dynamics. The architectures cover three types of families that are of potential interest in fuel cell membrane research. All architectures consist of connected hydrophobic backbone A beads, to which side chains are grafted. For the type I family, the hydrophilic (functional) C beads are pendent on (amphiphilic) [AxC] side chains. The type II architecture contains both hydrophobic [A4] and short hydrophilic [C] side chains. For type III, the C beads are embedded along various locations within the [AxCAy] side chains (x + y = constant). For similar equilibrium time, the membrane water volume fraction increases with side chain length x for type I, and for type III, it increases with the distance x that C beads are separated from the backbone. Among the architectures (types I and III) for which the number of covalent C-A bonds are the same, the water uptake increases with the average number of A-A and A-C bonds (dpd springs) between A beads and the nearest C bead. A picture emerges in which for similar ion exchange capacity model membranes water uptake increases as a function of ⟨Nbondphob-phyl⟩.
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Affiliation(s)
- G Dorenbos
- Private Researcher, Belle Crea 502, 1107-2 Susono 410-1118, Japan
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7
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Hager L, Hegelheimer M, Stonawski J, Freiberg ATS, Jaramillo-Hernández C, Abellán G, Hutzler A, Böhm T, Thiele S, Kerres J. Novel side chain functionalized polystyrene/O-PBI blends with high alkaline stability for anion exchange membrane water electrolysis (AEMWE). JOURNAL OF MATERIALS CHEMISTRY. A 2023; 11:22347-22359. [PMID: 38013811 PMCID: PMC10597322 DOI: 10.1039/d3ta02978f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 10/05/2023] [Indexed: 11/29/2023]
Abstract
We report the synthesis of a polystyrene-based anion exchange polymer bearing the cationic charge at a C6-spacer. The polymer is prepared by a functionalized monomer strategy. First, a copper halide catalyzed C-C coupling reaction between a styryl Grignard and 1,6-dibromohexane is applied, followed by quaternization with N-methylpiperidine and free radical polymerization. The novel polymer is blended with the polybenzimidazole O-PBI to yield mechanically stable blend membranes representing a new class of anion exchange membranes. In this regard, the ratio of the novel anion exchange polymer to O-PBI is varied to study the influence on water uptake and ionic conductivity. Blend membranes with IECs between 1.58 meq. OH- g-1 and 2.20 meq. OH- g-1 are prepared. The latter shows excellent performance in AEMWE, reaching 2.0 A cm-2 below 1.8 V in 1 M KOH at 70 °C, with a minor degradation rate from the start. The blend membranes show no conductivity loss after immersion in 1 M KOH at 85 °C for six weeks indicating high alkaline stability.
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Affiliation(s)
- Linus Hager
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Department of Chemical and Biological Engineering, Friedrich Alexander Universität Erlangen-Nürnberg Egerlandstr. 3 91058 Erlangen Germany
| | - Manuel Hegelheimer
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Department of Chemical and Biological Engineering, Friedrich Alexander Universität Erlangen-Nürnberg Egerlandstr. 3 91058 Erlangen Germany
| | - Julian Stonawski
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Department of Chemical and Biological Engineering, Friedrich Alexander Universität Erlangen-Nürnberg Egerlandstr. 3 91058 Erlangen Germany
| | - Anna T S Freiberg
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Department of Chemical and Biological Engineering, Friedrich Alexander Universität Erlangen-Nürnberg Egerlandstr. 3 91058 Erlangen Germany
| | | | - Gonzalo Abellán
- Institute of Molecular Science, University of Valencia c/ Catedrático José Beltrán 2 Paterna Spain
| | - Andreas Hutzler
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
| | - Thomas Böhm
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
| | - Simon Thiele
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Department of Chemical and Biological Engineering, Friedrich Alexander Universität Erlangen-Nürnberg Egerlandstr. 3 91058 Erlangen Germany
| | - Jochen Kerres
- Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11) Cauerstr. 1 91058 Erlangen Germany
- Chemical Resource Beneficiation Faculty of Natural Sciences, North-West University Potchefstroom 2520 South Africa
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8
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Cui R, Li S, Yu C, Zhou Y. The Evolution of Hydrogen Bond Network in Nafion via Molecular Dynamics Simulation. Macromolecules 2023. [DOI: 10.1021/acs.macromol.2c02106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Affiliation(s)
- Rui Cui
- School of Chemistry & Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Shanlong Li
- School of Chemistry & Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Chunyang Yu
- School of Chemistry & Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Yongfeng Zhou
- School of Chemistry & Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
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Zhu Z, Paddison SJ. Perspective: Morphology and ion transport in ion-containing polymers from multiscale modeling and simulations. Front Chem 2022; 10:981508. [PMID: 36059884 PMCID: PMC9437359 DOI: 10.3389/fchem.2022.981508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 07/14/2022] [Indexed: 11/20/2022] Open
Abstract
Ion-containing polymers are soft materials composed of polymeric chains and mobile ions. Over the past several decades they have been the focus of considerable research and development for their use as the electrolyte in energy conversion and storage devices. Recent and significant results obtained from multiscale simulations and modeling for proton exchange membranes (PEMs), anion exchange membranes (AEMs), and polymerized ionic liquids (polyILs) are reviewed. The interplay of morphology and ion transport is emphasized. We discuss the influences of polymer architecture, tethered ionic groups, rigidity of the backbone, solvents, and additives on both morphology and ion transport in terms of specific interactions. Novel design strategies are highlighted including precisely controlling molecular conformations to design highly ordered morphologies; tuning the solvation structure of hydronium or hydroxide ions in hydrated ion exchange membranes; turning negative ion-ion correlations to positive correlations to improve ionic conductivity in polyILs; and balancing the strength of noncovalent interactions. The design of single-ion conductors, well-defined supramolecular architectures with enhanced one-dimensional ion transport, and the understanding of the hierarchy of the specific interactions continue as challenges but promising goals for future research.
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Affiliation(s)
| | - Stephen J. Paddison
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, United States
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10
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Cui R, Li S, Yu C, Wang Y, Zhou Y. Understanding the mechanism of nitrogen transport in the perfluorinated sulfonic-acid hydrated membranes via molecular dynamics simulations. J Memb Sci 2022. [DOI: 10.1016/j.memsci.2022.120328] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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11
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Dubey V, Daschakraborty S. Translational Jump-Diffusion of Hydroxide Ion in Anion Exchange Membrane: Deciphering the Nature of Vehicular Diffusion. J Phys Chem B 2022; 126:2430-2440. [PMID: 35294202 DOI: 10.1021/acs.jpcb.2c00240] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Earlier, ab initio and reactive force-field-based molecular dynamics (MD) simulation studies suggested an overwhelming contribution of the vehicular diffusion in the total diffusion of hydroxide ions rather than structural diffusion. But does the vehicular diffusion occur via small-step displacement? This question is important to have an understanding of the real characteristics of vehicular diffusion. To answer this question, we perform a classical molecular dynamics simulation of a system containing a hydroxide ion exchange membrane polymer and hydroxide ion at different hydration levels and temperatures using the same molecular force field (Dubey, V. Chem. Phys. Lett. 2020, 755, 137802), which successfully captured the microscopic structure and dynamics of the system. We use the translational jump-diffusion approach, used previously in supercooled water for understanding the origin of breakdown of the Stokes-Einstein relation, to calculate the jump-diffusion coefficient of hydroxide ion and water in the anion exchange membrane. We have seen a significant role of hydration level and temperature in the mechanism of vehicular diffusion. In overhydrated membrane, both hydroxide ions and water molecules diffuse via both small- and large-step displacement. With decreasing hydration level and temperature, the diffusion is increasingly governed by the jump-diffusion mechanism. The larger contribution of jump-diffusion comes from the stronger caging of the diffusing species by the solvent at lower hydration levels and temperature. These results, therefore, suggest that the hydration level and temperature of the hydroxide ion exchange membrane determine the detailed mechanism of the vehicular diffusion of hydroxide ion, especially whether the diffusion follows hydrodynamics or not.
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Affiliation(s)
- Vikas Dubey
- Department of Chemistry, Indian Institute of Technology Patna, Bihar 801106, India
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12
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Jiménez-García JC, Olmos-Asar JA, Franceschini EA, Mariscal MM. Effect of Nafion content and hydration level on the electrochemical area of a Pt nanocatalyst in the triple-phase boundary. Phys Chem Chem Phys 2021; 23:27543-27551. [PMID: 34874379 DOI: 10.1039/d1cp03731e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Despite the great scientific effort, there are still some aspects of a polymeric membrane-based fuel cell (PEMFC) operation that are difficult to access experimentally. This is the case of the so-called triple-phase boundary (TPB), where the ionomer (commonly Nafion) interacts with the supported nanocatalyst (commonly Pt) and is key to the catalytic activity of the system. In this work, we use molecular dynamics simulations and electrochemical experiments on a Nafion/Pt/C system. We perform a systematic analysis, at an atomistic level, to evaluate the effect of several fundamental factors and their intercorrelation on the electrochemically active area (ECSA) of the catalysts. Our results reveal that at high Nafion contents, the catalyst utilization is affected due to the strong interaction between the sulfonic groups of the ionomer and the surface of the Pt nanoparticles (NPs). On the other hand, when the hydration level of the membrane decreases, the sulfonic groups have a greater occupation on the NP surface, covering the active area with hydrophobic Nafion chains and therefore increasing the inactive area. Voltammograms can corroborate our calculations. Overall, this investigation allows us to rationalize how the catalyst utilization is affected, which is an important step in establishing the relationship between the environment and the effectiveness and durability of the PEMFC system.
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Affiliation(s)
- Juan C Jiménez-García
- Instituto de Investigaciones en Fisico-Química de Córdoba (INFIQC) - CONICET, Córdoba, Argentina. .,Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Jimena A Olmos-Asar
- Instituto de Investigaciones en Fisico-Química de Córdoba (INFIQC) - CONICET, Córdoba, Argentina. .,Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Esteban A Franceschini
- Instituto de Investigaciones en Fisico-Química de Córdoba (INFIQC) - CONICET, Córdoba, Argentina. .,Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Marcelo M Mariscal
- Instituto de Investigaciones en Fisico-Química de Córdoba (INFIQC) - CONICET, Córdoba, Argentina. .,Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
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13
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Okushima S, Hasegawa S, Kawakatsu T, Maekawa Y. Coarse-grained molecular dynamics simulation to reproduce phase-separated structures in graft-type polymer electrolyte membranes. POLYMER 2021. [DOI: 10.1016/j.polymer.2021.124036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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14
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Cheng RH, Cai H, Huang YR, Cui X, Chen Z, Chen HY, Ding S. A broad-range variable-temperature solid state NMR spectral and relaxation investigation of the water state in Nafion 117. Phys Chem Chem Phys 2021; 23:10899-10908. [PMID: 33908418 DOI: 10.1039/c9cp05978d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Understanding the water state in Nafion is not only crucial for operating a proton-exchange membrane (PEM)-based fuel cell, but also intimately related to the elucidation of the proton transport mechanism in a PEM. Although many studies have been published on this subject, some controversies and ambiguities remain unresolved. In this work, we design three different types of Nafion samples by substituting protons with lithium or sodium cations. We also pay special attention to the preparation of samples for carrying out broad-range variable temperature solid state NMR experiments so that no membrane dehydration occurs during the long experimental time at low temperatures. With these precautions and improvements, clear and largely straightforward information could be obtained to ensure minimal ambiguity and complexity in the interpretation of the experimental data. Our results show that about 40-60% of water remains unfrozen at -70 °C, depending on the type of the substituting cation. Both the 1H and 2H spectral and relaxation results indicate that water freezing starts from the center of the nanopores inside Nafion and increases gradually as the temperature decreases. The protons remain dissociated with sulfonate groups even at the lowest temperature we reached (-70 °C), whereas both lithium and sodium are associated with sulfonate groups at most temperatures below 0 °C. The experimental data also suggest that besides frozen and unfrozen water, there is broad distribution of water state and dynamics in Nafion as the temperature is lowered from above zero down to -70 °C. The effect of the size of the substituting cation significantly affects the properties of supercooled water by modifying the cation-water interaction and impeding the rotation of sulfonate groups. These novel results not only help us in establishing a better understanding of the water state in Nafion and its performance as a proton exchange mebrane, but also provide insights into water freezing, antifreeze and supercooling in other nanoscopic environments.
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Affiliation(s)
- Ren-Hao Cheng
- Department of Chemistry and Center for Nanoscience and Nanotechnology, National Sun Yat-sen University, 70 Lien-Hai Road, Kaohsiung, 80424, Taiwan.
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15
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Crosslinked Proton Exchange Membranes with a Wider Working Temperature Based on Phosphonic Acid Functionalized Siloxane and PPO. Macromol Res 2021. [DOI: 10.1007/s13233-021-9024-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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16
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Zhorov BS. Possible Mechanism of Ion Selectivity in Eukaryotic Voltage-Gated Sodium Channels. J Phys Chem B 2021; 125:2074-2088. [DOI: 10.1021/acs.jpcb.0c11181] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Boris S. Zhorov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8K 4K1, Canada
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg 194223, Russian Federation
- Almazov National Medical Research Centre, St. Petersburg 197341, Russian Federation
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17
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Kuo AT, Urata S, Nakabayashi K, Watabe H, Honmura S. Coarse-Grained Molecular Dynamics Simulation of Perfluorosulfonic Acid Polymer in Water–Ethanol Mixtures. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02364] [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)
- An-Tsung Kuo
- Innovative Technology Laboratories, AGC Inc., Yokohama 230-0045, Japan
| | - Shingo Urata
- Innovative Technology Laboratories, AGC Inc., Yokohama 230-0045, Japan
| | | | - Hiroyuki Watabe
- Materials Integration Laboratories, AGC Inc., Yokohama 230-0045, Japan
| | - Satoru Honmura
- Materials Integration Laboratories, AGC Inc., Yokohama 230-0045, Japan
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18
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Dubey V, Maiti A, Daschakraborty S. Predicting the solvation structure and vehicular diffusion of hydroxide ion in an anion exchange membrane using nonreactive molecular dynamics simulation. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137802] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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19
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Elton DC, Spencer PD, Riches JD, Williams ED. Exclusion Zone Phenomena in Water-A Critical Review of Experimental Findings and Theories. Int J Mol Sci 2020; 21:E5041. [PMID: 32708867 PMCID: PMC7404113 DOI: 10.3390/ijms21145041] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Revised: 06/27/2020] [Accepted: 07/13/2020] [Indexed: 12/29/2022] Open
Abstract
The existence of the exclusion zone (EZ), a layer of water in which plastic microspheres are repelled from hydrophilic surfaces, has now been independently demonstrated by several groups. A better understanding of the mechanisms which generate EZs would help with understanding the possible importance of EZs in biology and in engineering applications such as filtration and microfluidics. Here we review the experimental evidence for EZ phenomena in water and the major theories that have been proposed. We review experimental results from birefringence, neutron radiography, nuclear magnetic resonance, and other studies. Pollack theorizes that water in the EZ exists has a different structure than bulk water, and that this accounts for the EZ. We present several alternative explanations for EZs and argue that Schurr's theory based on diffusiophoresis presents a compelling alternative explanation for the core EZ phenomenon. Among other things, Schurr's theory makes predictions about the growth of the EZ with time which have been confirmed by Florea et al. and others. We also touch on several possible confounding factors that make experimentation on EZs difficult, such as charged surface groups, dissolved solutes, and adsorbed nanobubbles.
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Affiliation(s)
- Daniel C Elton
- Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, MD 20892, USA
| | - Peter D Spencer
- School of Biomedical Sciences, Faculty of Health, Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, QLD 4059, Australia
| | - James D Riches
- School of Earth, Environmental and Biological Sciences, Science and Engineering Faculty, Institute for Future Environments, QUT, Brisbane, QLD 4000, Australia
| | - Elizabeth D Williams
- School of Biomedical Sciences, Faculty of Health, Institute of Health and Biomedical Innovation, QUT, Australian Prostate Cancer Research Centre-Queensland, Translational Research Institute, Brisbane, QLD 4059, Australia
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20
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Dissipative Particle Dynamics Modeling of Polyelectrolyte Membrane-Water Interfaces. Polymers (Basel) 2020; 12:polym12040907. [PMID: 32295222 PMCID: PMC7240515 DOI: 10.3390/polym12040907] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 04/10/2020] [Accepted: 04/11/2020] [Indexed: 12/03/2022] Open
Abstract
Previous experiments of water vapor penetration into polyelectrolyte membrane (PEM) thin films have indicated the influence of the water concentration gradient and polymer chemistry on the interface evolution, which will eventually affect the efficiency of the fuel cell operation. Moreover, PEMs of different side chains have shown differences in water cluster structure and diffusion. The evolution of the interface between water and polyelectrolyte membranes (PEMs), which are used in fuel cells and flow batteries, of three different side-chain lengths has been studied using dissipative particle dynamics (DPD) simulations. Higher and faster water uptake is usually beneficial in the operation of fuel cells and flow batteries. The simulated water uptake increased with the increasing side chain length. In addition, the water uptake was rapid initially and slowed down afterwards, which is in agreement with the experimental observations. The water cluster formation rate was also found to increase with the increasing side-chain length, whereas the water cluster shapes were unaffected. Water diffusion in the membranes, which affects proton mobility in the PEMs, increased with the side-chain length at all distances from the interface. In conclusion, side-chain length was found to have a strong influence on the interface water structure and water penetration rates, which can be harnessed for the better design of PEMs. Since the PEM can undergo cycles of dehydration and rehydration, faster water uptake increases the efficiency of these devices. We show that the longer side chains with backbone structure similar to Nafion should be more suitable for fuel cell/flow battery usage.
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21
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Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses. ENERGIES 2020. [DOI: 10.3390/en13020420] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Innovative renewable routes are potentially able to sustain the transition to a decarbonized energy economy. Green synthetic fuels, including hydrogen and natural gas, are considered viable alternatives to fossil fuels. Indeed, they play a fundamental role in those sectors that are difficult to electrify (e.g., road mobility or high-heat industrial processes), are capable of mitigating problems related to flexibility and instantaneous balance of the electric grid, are suitable for large-size and long-term storage and can be transported through the gas network. This article is an overview of the overall supply chain, including production, transport, storage and end uses. Available fuel conversion technologies use renewable energy for the catalytic conversion of non-fossil feedstocks into hydrogen and syngas. We will show how relevant technologies involve thermochemical, electrochemical and photochemical processes. The syngas quality can be improved by catalytic CO and CO2 methanation reactions for the generation of synthetic natural gas. Finally, the produced gaseous fuels could follow several pathways for transport and lead to different final uses. Therefore, storage alternatives and gas interchangeability requirements for the safe injection of green fuels in the natural gas network and fuel cells are outlined. Nevertheless, the effects of gas quality on combustion emissions and safety are considered.
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22
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Sengupta S, Lyulin AV. Molecular Modeling of Structure and Dynamics of Nafion Protonation States. J Phys Chem B 2019; 123:6882-6891. [PMID: 31306017 PMCID: PMC6691399 DOI: 10.1021/acs.jpcb.9b04534] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 07/08/2019] [Indexed: 11/29/2022]
Abstract
We present the results of the atomistic molecular dynamics modeling of different protonation states of Nafion at varying hydration levels. Previous experiments have shown that the degree of deprotonation (DDP) of the sulfonic acid groups in a Nafion membrane varies significantly upon hydration. Our goal is to provide insights into the effects of variable protonation states and water content on the internal structure and vehicular transport inside the Nafion membrane. The Nafion side chain lengths showed a weak increasing trend with increasing DDP at all hydration levels, exposing more of the sulfonic acid groups to the hydrophilic/water phase. The water-phase characteristic size/diameter decreased with increasing DDP, but, interestingly, the average number of water molecules per cluster increased. The probability of water-hydronium hydrogen bond formation decreased with increasing DDP, despite an increase in the total number of such hydrogen bonds. The water diffusion was largely unaffected by the state of deprotonation. In contrast to that, the hydronium ion diffusion slowed down with increasing DDP in the overall membrane. The hydronium ion residence times around the sulfonic acid group increased with increasing DDP. Our simulations show a strong connection between the morphology of the water domains and protonation states of Nafion. Such a connection can also be expected in polyelectrolyte membranes similar to Nafion.
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Affiliation(s)
- Soumyadipta Sengupta
- Theory
of Polymers and Soft Matter, Department of Applied Physics, and Center for Computational
Energy Research, Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands
| | - Alexey V. Lyulin
- Theory
of Polymers and Soft Matter, Department of Applied Physics, and Center for Computational
Energy Research, Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands
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23
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Coarse-grained study of the effect of hydrophobic side chain length on cluster size distributions and water diffusion in (amphiphilic-hydrophobic) multi-block co-polymer membranes. POLYMER 2019. [DOI: 10.1016/j.polymer.2019.04.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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24
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Akbari S, Hamed Mosavian MT, Moosavi F, Ahmadpour A. Elucidating the morphological aspects and proton dynamics in a hybrid perfluorosulfonic acid membrane for medium-temperature fuel cell applications. Phys Chem Chem Phys 2018; 20:29778-29789. [PMID: 30462118 DOI: 10.1039/c8cp05377d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
A perfluorosulfonic acid (PFSA) membrane, i.e. Nafion® 117, was doped with the heteropoly salts (HPS) Cs3PW12O40, Rb3PW12O40, and (NH4)3PW12O40. Also, composite membranes with CsxH3-xPW12O40 (x = 1, 2, and 3) as dopants were investigated, which were rendered insoluble by substituting protons with larger cations. Morphological assessment and a detailed analysis of the hopping events via SAXS measurement and analysis of the hydrogen bond networks were performed using classical and quantum hopping molecular dynamics simulation. The phase segregation decreased by increasing the extent proton substitution in HPA. HPS containing cations with a larger ionic radius induced smaller phase segregation in the membrane, as confirmed by the RDF plots. SAXS simulation revealed that the hydrophilic phase domains in the HPS-doped Nafion® membrane were spaced further apart than that in the HPA-doped membrane. Although there was a greater number of isolated clusters for the Cs3PW12O40-doped Nafion®, the average number of cluster decreased with an increase in the substitution cation/proton ratio and ionic radius of the cation. The analysis of the H-bond network stability revealed that the proton hops slower when the membrane contains HPS particles and the mean residence time of a proton on water molecules increases with an increase in the extent of proton substitution in H3PW12O40. Indeed, for the HPA-doped membrane, the diffusion of water molecules is lower than that in the HPS-doped system.
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Affiliation(s)
- Saeed Akbari
- Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran.
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25
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Extrusion of Nafion and Aquivion membranes: environmentally friendly procedure and good conductivities. Polym Bull (Berl) 2018. [DOI: 10.1007/s00289-018-2427-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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26
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Sengupta S, Lyulin AV. Molecular Dynamics Simulations of Substrate Hydrophilicity and Confinement Effects in Capped Nafion Films. J Phys Chem B 2018; 122:6107-6119. [PMID: 29757641 PMCID: PMC5994720 DOI: 10.1021/acs.jpcb.8b03257] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 05/14/2018] [Indexed: 01/25/2023]
Abstract
Nafion nanocomposites for energy-related applications are being used extensively because of the attractive properties such as enhanced water retention, low unwanted crossover of electrolytes, and high proton conductivity. We present the results of the molecular dynamics modeling of Nafion films confined between two walls (substrates) of different polymer-wall interaction strengths and of different separation distances to model Nafion nanocomposites. Our goal is to provide insights into the effects of varying hydrophilicity and volume fraction of fillers/nanoparticles on the internal structure and water transport inside the Nafion membrane. The sulfur-sulfur radial distribution function first peak distance and the sulfur-oxygen (water) coordination number in the first hydration shell were negligibly affected by the wall (substrate) hydrophilicity or the film thickness. The Nafion side chains were found to bend toward the substrates with high hydrophilicity which is in qualitative agreement with existing experiments. The amount of bending was observed to reduce with increasing film thickness. However, the side-chain length did not show any noticeable variation with wall (substrate) hydrophilicity or film thickness. The water clusters became smaller and more isolated clusters emerged for highly hydrophilic substrates. In addition, the water cluster sizes showed a decreasing trend with decreasing film thickness in the case of hydrophilic substrates, which has also been observed in experiments of supported Nafion films. The in-plane water diffusion was enhanced considerably for hydrophilic substrates, and this mechanism has also been proposed previously in experiments. The in-plane water diffusion was also found to be a strong function of the substrate selectivity toward the hydrophilic phase. Our simulations can help provide more insights to experimentalists for choosing or modifying nanoparticles for Nafion nanocomposites.
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Affiliation(s)
- Soumyadipta Sengupta
- Theory
of Polymers and Soft Matter, Department of Applied Physics, and Center for Computational
Energy Research, Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands
| | - Alexey V. Lyulin
- Theory
of Polymers and Soft Matter, Department of Applied Physics, and Center for Computational
Energy Research, Department of Applied Physics, Eindhoven University of Technology, Eindhoven 5600 MB, The Netherlands
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27
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Exploring the effect of pendent side chain length on the structural and mechanical properties of hydrated perfluorosulfonic acid polymer membranes by molecular dynamics simulation. POLYMER 2018. [DOI: 10.1016/j.polymer.2018.05.033] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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28
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Mabuchi T, Tokumasu T. Relationship between Proton Transport and Morphology of Perfluorosulfonic Acid Membranes: A Reactive Molecular Dynamics Approach. J Phys Chem B 2018; 122:5922-5932. [DOI: 10.1021/acs.jpcb.8b02318] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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29
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Okuwaki K, Mochizuki Y, Doi H, Kawada S, Ozawa T, Yasuoka K. Theoretical analyses on water cluster structures in polymer electrolyte membrane by using dissipative particle dynamics simulations with fragment molecular orbital based effective parameters. RSC Adv 2018; 8:34582-34595. [PMID: 35548624 PMCID: PMC9086946 DOI: 10.1039/c8ra07428c] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/01/2018] [Indexed: 12/04/2022] Open
Abstract
The mesoscopic structures of polymer electrolyte membrane (PEM) affect the performances of fuel cells. Nafion® with the Teflon® backbone has been the most widely used of all PEMs, but sulfonated poly-ether ether-ketone (SPEEK) having an aromatic backbone has drawn interest as an alternative to Nafion. In the present study, a series of dissipative particle dynamics (DPD) simulations were performed to compare Nafion and SPEEK. These PEM polymers were modeled by connected particles corresponding to the hydrophobic backbone and the hydrophilic moiety of sulfonic acid group. The water particle interacting with Nafion particles was prepared as well. The crucial interaction parameters among DPD particles were evaluated by a series of calculations based on the fragment molecular orbital (FMO) method in a non-empirical way (Okuwaki et al., J. Phys. Chem. B, 2018, 122, 338–347). Through the DPD simulations, the water and hydrophilic particles aggregated, forming cluster networks surrounded by the hydrophobic phase. The structural features of formed water clusters were investigated in detail. Furthermore, the differences in percolation behaviors between Nafion and SPEEK revealed much better connectivity among water clusters by Nafion. The present FMO-DPD simulation results were in good agreement with available experimental data. The mesoscopic structures of polymer electrolyte membrane (PEM) affect the performances of fuel cells.![]()
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Affiliation(s)
- Koji Okuwaki
- Department of Chemistry and Research Center for Smart Molecules
- Faculty of Science
- Rikkyo University
- Toshima-ku
- Japan
| | - Yuji Mochizuki
- Department of Chemistry and Research Center for Smart Molecules
- Faculty of Science
- Rikkyo University
- Toshima-ku
- Japan
| | - Hideo Doi
- Department of Chemistry and Research Center for Smart Molecules
- Faculty of Science
- Rikkyo University
- Toshima-ku
- Japan
| | - Shutaro Kawada
- Department of Chemistry and Research Center for Smart Molecules
- Faculty of Science
- Rikkyo University
- Toshima-ku
- Japan
| | | | - Kenji Yasuoka
- Department of Mechanical Engineering
- Keio University
- Yokohama 223-8522
- Japan
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30
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Abstract
An important limitation of standard classical molecular dynamics simulations is the inability to make or break chemical bonds. This restricts severely our ability to study processes that involve even the simplest of chemical reactions, the transfer of a proton. Existing approaches for allowing proton transfer in the context of classical mechanics are rather cumbersome and have not achieved widespread use and routine status. Here we reconsider the combination of molecular dynamics with periodic stochastic proton hops. To ensure computational efficiency, we propose a non-Boltzmann acceptance criterion that is heuristically adjusted to maintain the correct or desirable thermodynamic equilibria between different protonation states and proton transfer rates. Parameters are proposed for hydronium, Asp, Glu, and His. The algorithm is implemented in the program CHARMM and tested on proton diffusion in bulk water and carbon nanotubes and on proton conductance in the gramicidin A channel. Using hopping parameters determined from proton diffusion in bulk water, the model reproduces the enhanced proton diffusivity in carbon nanotubes and gives a reasonable estimate of the proton conductance in gramicidin A.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York/CUNY , 160 Convent Avenue, New York, New York 10031, United States.,Graduate Programs in Chemistry, Biochemistry & Physics, Graduate Center, City University of New York , 365 Fifth Ave, New York, New York 10016, United States
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics , Max-von-Laue Strasse 3, 60438 Frankfurt am Main, Germany
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31
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Akbari S, Mosavian MTH, Ahmadpour A, Moosavi F. Water Dynamics and Proton-Transport Mechanisms of Nafion 117/Phosphotungstic Acid Composite Membrane: A Molecular Dynamics Study. Chemphyschem 2017; 18:3485-3497. [DOI: 10.1002/cphc.201700725] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 09/11/2017] [Indexed: 10/18/2022]
Affiliation(s)
- Saeed Akbari
- Chemical Engineering Department; Faculty of Engineering; Ferdowsi University of Mashhad; Iran
| | | | - Ali Ahmadpour
- Chemical Engineering Department; Faculty of Engineering; Ferdowsi University of Mashhad; Iran
| | - Fatemeh Moosavi
- Department of Chemistry; Faculty of Science, Ferdows; University of Mashhad Iran
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32
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Affiliation(s)
- Santanu Roy
- Physical Science Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
| | - Marcel D. Baer
- Physical Science Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
| | - Christopher J. Mundy
- Physical Science Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
| | - Gregory K. Schenter
- Physical Science Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States
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33
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Zhang W, van Duin ACT. Second-Generation ReaxFF Water Force Field: Improvements in the Description of Water Density and OH-Anion Diffusion. J Phys Chem B 2017; 121:6021-6032. [DOI: 10.1021/acs.jpcb.7b02548] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Weiwei Zhang
- Department of Mechanical
and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Adri C. T. van Duin
- Department of Mechanical
and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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34
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Tripathy M, Kumar PBS, Deshpande AP. Molecular Structuring and Percolation Transition in Hydrated Sulfonated Poly(ether ether ketone) Membranes. J Phys Chem B 2017; 121:4873-4884. [PMID: 28430444 DOI: 10.1021/acs.jpcb.7b01045] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The extent of phase separation and water percolation in sulfonated membranes are the key to their performance in fuel cells. Toward this, the effect of hydration on the morphology and transport characteristics of sulfonated poly(ether ether ketone), sPEEK, membrane is investigated using atomistic molecular dynamics simulation at various hydration levels(λ: number of water molecules per sulfonate group). The evolution of local morphology is investigated using structural correlations and minimum pair distances. Transport properties are probed using mean squared displacements and diffusion coefficients. The water-sulfonate interaction in sPEEK is found to be stronger than that in Nafion, as observed in experiments. Analyses indicate the presence of narrow connected path of water and hydronium at λ = 4 and large domains, spanning half the simulation box, at λ = 15. The behavior of membrane water remains far from bulk as indicated by its diffusion coefficient. The persistence of small isolated water clusters demonstrates the extent of phase separation in sPEEK to be lesser than that in Nafion. Analyses at molecular and collective levels suggest the occurrence of a percolation transition between λ = 8 and 10, which leads to a connected network of water channels in the membrane, thereby boosting the hydronium mobility.
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Affiliation(s)
- Madhusmita Tripathy
- Department of Physics, Indian Institute of Technology Madras , Chennai, Tamil Nadu, 600036, India
| | - P B Sunil Kumar
- Department of Physics, Indian Institute of Technology Madras , Chennai, Tamil Nadu, 600036, India
| | - Abhijit P Deshpande
- Department of Chemical Engineering, Indian Institute of Technology Madras , Chennai, Tamil Nadu, 600036, India
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35
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Thomaz JE, Lawler CM, Fayer MD. Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights. J Phys Chem B 2017; 121:4544-4553. [PMID: 28398064 DOI: 10.1021/acs.jpcb.7b01764] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.
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Affiliation(s)
- Joseph E Thomaz
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Christian M Lawler
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Michael D Fayer
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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36
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Lu J, Miller C, Molinero V. Parameterization of a coarse-grained model with short-ranged interactions for modeling fuel cell membranes with controlled water uptake. Phys Chem Chem Phys 2017; 19:17698-17707. [PMID: 28653074 DOI: 10.1039/c7cp02281f] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The coarse-grained model FFpvap reproduces the experimental activity coefficient of water in tetramethylammonium chloride solutions over a wide range of concentrations, with a hundred-fold gain in computing efficiency with respect to atomistic models.
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Affiliation(s)
- Jibao Lu
- Department of Chemistry
- The University of Utah
- Salt Lake City
- USA
| | - Chance Miller
- Department of Chemistry
- The University of Utah
- Salt Lake City
- USA
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37
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Lu J, Jacobson LC, Perez Sirkin YA, Molinero V. High-Resolution Coarse-Grained Model of Hydrated Anion-Exchange Membranes that Accounts for Hydrophobic and Ionic Interactions through Short-Ranged Potentials. J Chem Theory Comput 2016; 13:245-264. [PMID: 28068769 DOI: 10.1021/acs.jctc.6b00874] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Jibao Lu
- Department
of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - Liam C. Jacobson
- Department
of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States
| | - Yamila A. Perez Sirkin
- Departamento
de Química Inorgánica, Analítica y Química
Física, and INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina
| | - Valeria Molinero
- Department
of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States
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38
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Schalenbach M, Lueke W, Lehnert W, Stolten D. The influence of water channel geometry and proton mobility on the conductivity of Nafion®. Electrochim Acta 2016. [DOI: 10.1016/j.electacta.2016.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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39
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Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow. Sci Rep 2016; 6:29484. [PMID: 27388562 PMCID: PMC4937448 DOI: 10.1038/srep29484] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 06/16/2016] [Indexed: 12/23/2022] Open
Abstract
Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.
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40
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Dorenbos G. Water Diffusion Dependence on Amphiphilic Block Design in (Amphiphilic-Hydrophobic) Diblock Copolymer Membranes. J Phys Chem B 2016; 120:5634-45. [PMID: 27266679 DOI: 10.1021/acs.jpcb.6b03171] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polyelectrolyte membranes (PEMs) are applied in polyelectrolyte fuel cells (PEFC). The proton conductive pathways within PEMs are provided by nanometer-sized water containing pores. Large-scale application of PEFC requires the production of low-cost membranes with high proton conductivity and therefore good connected pore networks. Pore network formation within four alternative model diblock (hydrophobic_amphiphilic) copolymers in the presence of water is studied by dissipative particle dynamics. Each hydrophobic block contains 50 consecutively connected hydrophobic (A) fragments, and amphiphilic blocks contain 40 hydrophobic A beads and 10 hydrophilic C beads. For one amphiphilic block the C beads are distributed uniformly along the backbone. For the other architectures C beads are located at the end of the side chains attached at regular intervals along the backbone. Water diffusion through the pores is modeled by Monte Carlo tracer diffusion through mapped morphologies. Diffusion is highest for the grafted architectures and increases with increase of length of the side chains. A consistent picture emerges in which diffusion strongly increases with the value of ⟨Nbond⟩ within the amphiphilic block, where ⟨Nbond⟩ is the average number of bonds between hydrophobic A beads and the nearest C bead.
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Affiliation(s)
- Gert Dorenbos
- T410-1118, sano 1107-2, Belle Crea 502, Susono, Japan
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41
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Roy S, Skoff D, Perroni DV, Mondal J, Yethiraj A, Mahanthappa MK, Zanni MT, Skinner JL. Water Dynamics in Gyroid Phases of Self-Assembled Gemini Surfactants. J Am Chem Soc 2016; 138:2472-5. [DOI: 10.1021/jacs.5b12370] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Santanu Roy
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - David Skoff
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - Dominic V. Perroni
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - Jagannath Mondal
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - Arun Yethiraj
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - Mahesh K. Mahanthappa
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - Martin T. Zanni
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
| | - James L. Skinner
- Department of Chemistry, University of Wisconsin, 1101 University
Avenue, Madison, Wisconsin 53706, United States
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42
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Dorenbos G. Modelling linear and branched amphiphilic star polymer electrolyte membranes and verification of the bond counting method. RSC Adv 2016. [DOI: 10.1039/c5ra24172c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Water diffusion through hydrated amphiphilic star polymer membranes depends strongly on hydrophilic position within the linear and Y-shaped arms.
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43
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High temperature proton exchange membranes with enhanced proton conductivities at low humidity and high temperature based on polymer blends and block copolymers of poly(1,3-cyclohexadiene) and poly(ethylene glycol). POLYMER 2015. [DOI: 10.1016/j.polymer.2015.09.033] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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44
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Dorenbos G. Morphology and diffusion within model membranes: Application of bond counting method to architectures with bimodal side chain length distributions. Eur Polym J 2015. [DOI: 10.1016/j.eurpolymj.2015.05.028] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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45
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Dorenbos G. Searching for low percolation thresholds within amphiphilic polymer membranes: The effect of side chain branching. J Chem Phys 2015; 142:224902. [DOI: 10.1063/1.4922156] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
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46
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Dorenbos G. Water diffusion within hydrated model grafted polymeric membranes with bimodal side chain length distributions. SOFT MATTER 2015; 11:2794-2805. [PMID: 25703230 DOI: 10.1039/c5sm00016e] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The effect of bimodal side chain length distributions on pore morphology and solvent diffusion within hydrated amphiphilic polymeric membranes is predicted. Seven polymeric architectures are constructed from hydrophobic backbones from which at regular intervals side chains branch off that are alternatingly short (composed of p hydrophobic A fragments or beads) and long (q A fragments, q > p). The side chains are end-linked with a hydrophilic C fragment. Pore morphologies at a water volume fraction of 0.16 are calculated by dissipative particle dynamics (DPD). Water diffusion through the water containing pores is calculated by tracer diffusion calculations through 140 selected snapshots and from the water bead motions. Diffusion constants decrease with difference in side chain lengths, q - p. Overall, the distance between pores also decreases with q - p. The results are explained by counting for every architecture the average number of bonds 〈N(bond)〉 between an A and the nearest C fragment. These results are in line with a database that contains more than 60 architectures. Diffusion constants tend to increase linearly with 〈N(bond)〉|C|(-1)|A|, where |C| and |A| are the C and A bead fractions within the architecture. 〈N(bond)〉 is therefore expected to be an interesting design parameter for obtaining low percolation thresholds for solvent and/or proton diffusion.
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Affiliation(s)
- G Dorenbos
- 410-1118, 1107-2 sano, Belle Crea 502, Susono-shi, Shizuoka-ken, Japan.
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47
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Kumar M, Venkatnathan A. Quantum Chemistry Study of Proton Transport in Imidazole Chains. J Phys Chem B 2015; 119:3213-22. [DOI: 10.1021/jp508994c] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Milan Kumar
- Department
of Chemical Engineering, Rajiv Gandhi Institute of Petroleum Technology, Rae Bareli 229316, Uttar Pradesh, India
| | - Arun Venkatnathan
- Department
of Chemistry, Indian Institute of Science Education and Research, Pune 411008, Maharashtra, India
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48
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Berrod Q, Lyonnard S, Guillermo A, Ollivier J, Frick B, Gébel G. QENS investigation of proton confined motions in hydrated perfluorinated sulfonic membranes and self-assembled surfactants. EPJ WEB OF CONFERENCES 2015. [DOI: 10.1051/epjconf/20158302002] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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49
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Daly KB, Panagiotopoulos AZ, Debenedetti PG, Benziger JB. Viscosity of Nafion Oligomers as a Function of Hydration and Counterion Type: A Molecular Dynamics Study. J Phys Chem B 2014; 118:13981-91. [DOI: 10.1021/jp509061z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Kevin B. Daly
- Department
of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
| | | | - Pablo G. Debenedetti
- Department
of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
| | - Jay B. Benziger
- Department
of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States
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50
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Davis EM, Stafford CM, Page KA. Elucidating Water Transport Mechanisms in Nafion Thin Films. ACS Macro Lett 2014; 3:1029-1035. [PMID: 35610787 DOI: 10.1021/mz500515b] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Ion-exchange membranes are critical components of hydrogen fuel cells, where these ionomers can be confined to nanoscale thicknesses, altering the physical properties of these films from that of bulk membranes. Therefore, it is important to develop methods capable of measuring and elucidating the transport mechanisms under thin film confinement compared to bulk Nafion. In this study, water sorption and diffusion in a Nafion thin film were measured using time-resolved in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Interfacial mass transport limitations were confirmed to be minimal, while restricted water diffusion was observed, where the effective diffusion coefficient of water in the thin Nafion film was many orders of magnitude lower (between 4 and 5 orders of magnitude) than those reported for bulk membranes and was dependent on the initial hydration state of the Nafion. Furthermore, the response of the hydrophobic domains (Teflon backbone) to the swelling of the hydrophilic domains (ionic clusters) was shown to be orders of magnitude slower than that of bulk Nafion.
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Affiliation(s)
- Eric M. Davis
- Materials
Science and Engineering
Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Christopher M. Stafford
- Materials
Science and Engineering
Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Kirt A. Page
- Materials
Science and Engineering
Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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