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Title: Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids

Abstract

The unique properties of ionic liquids (ILs) have made them promising candidates for electrochemical applications. Polymerization of the corresponding ILs results in a new class of materials called polymerized ionic liquids (PolyILs). Though PolyILs offer the possibility to combine the high conductivity of ILs and the high mechanical strength of polymers, their conductivities are typically much lower than that of the corresponding small molecule ILs. In this study, seven PolyILs were synthesized having degrees of polymerization ranging from 1 to 333, corresponding to molecular weights (MW) from 482 to 160 400 g/mol. Depolarized dynamic light scattering, broadband dielectric spectroscopy, rheology, and differential scanning calorimetry were employed to systematically study the influence of MW on the mechanism of ionic transport and segmental dynamics in these materials. Finally, the modified Walden plot analysis reveals that the ion conductivity transforms from being closely coupled with structural relaxation to being strongly decoupled from it as MW increases.

Authors:
 [1];  [2];  [1];  [1];  [2];  [1];  [1];  [2];  [1];  [3];  [4]
  1. Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Tennessee, Knoxville, TN (United States) ; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Univ. of Tennessee, Knoxville, TN (United States) ; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Temperature Materials Lab. (HTML)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1271895
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 49; Journal Issue: 12; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Fan, Fei, Wang, Weiyu, Holt, Adam P., Feng, Hongbo, Uhrig, David, Lu, Xinyi, Hong, Tao, Wang, Yangyang, Kang, Nam-Goo, Mays, Jimmy, and Sokolov, Alexei P.. Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids. United States: N. p., 2016. Web. doi:10.1021/acs.macromol.6b00714.
Fan, Fei, Wang, Weiyu, Holt, Adam P., Feng, Hongbo, Uhrig, David, Lu, Xinyi, Hong, Tao, Wang, Yangyang, Kang, Nam-Goo, Mays, Jimmy, & Sokolov, Alexei P.. Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids. United States. doi:10.1021/acs.macromol.6b00714.
Fan, Fei, Wang, Weiyu, Holt, Adam P., Feng, Hongbo, Uhrig, David, Lu, Xinyi, Hong, Tao, Wang, Yangyang, Kang, Nam-Goo, Mays, Jimmy, and Sokolov, Alexei P.. Tue . "Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids". United States. doi:10.1021/acs.macromol.6b00714. https://www.osti.gov/servlets/purl/1271895.
@article{osti_1271895,
title = {Effect of Molecular Weight on the Ion Transport Mechanism in Polymerized Ionic Liquids},
author = {Fan, Fei and Wang, Weiyu and Holt, Adam P. and Feng, Hongbo and Uhrig, David and Lu, Xinyi and Hong, Tao and Wang, Yangyang and Kang, Nam-Goo and Mays, Jimmy and Sokolov, Alexei P.},
abstractNote = {The unique properties of ionic liquids (ILs) have made them promising candidates for electrochemical applications. Polymerization of the corresponding ILs results in a new class of materials called polymerized ionic liquids (PolyILs). Though PolyILs offer the possibility to combine the high conductivity of ILs and the high mechanical strength of polymers, their conductivities are typically much lower than that of the corresponding small molecule ILs. In this study, seven PolyILs were synthesized having degrees of polymerization ranging from 1 to 333, corresponding to molecular weights (MW) from 482 to 160 400 g/mol. Depolarized dynamic light scattering, broadband dielectric spectroscopy, rheology, and differential scanning calorimetry were employed to systematically study the influence of MW on the mechanism of ionic transport and segmental dynamics in these materials. Finally, the modified Walden plot analysis reveals that the ion conductivity transforms from being closely coupled with structural relaxation to being strongly decoupled from it as MW increases.},
doi = {10.1021/acs.macromol.6b00714},
journal = {Macromolecules},
number = 12,
volume = 49,
place = {United States},
year = {Tue Jun 07 00:00:00 EDT 2016},
month = {Tue Jun 07 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 18works
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  • Polymerized ionic liquids (polyILs), composed mostly of organic ions covalently bonded to the polymer backbone and free counterions, are considered as an ideal electrolytes for various electrochemical devices, including fuel cells, supercapacitors and batteries. Despite large structural diversity of these systems, all of them reveal a universal but poorly understood feature - a charge transport faster than the segmental dynamics. Here, to address this issue, we have studied three novel polymer electrolyte membrane for fuel cells as well as four single-ion conductors including highly conductive siloxane-based polyIL. Our ambient and high pressure studies revealed fundamental differences in the conducting propertiesmore » of the examined systems. Finally, we demonstrate that the proposed methodology is a powerful tool to identify the charge transport mechanism in polyILs in general and thereby contribute to unraveling the microscopic nature of the decoupling phenomenon in these materials.« less
  • Conductivity in polymer electrolytes has been generally discussed with the assumption that the segmental motions control charge transport. However, much less attention has been paid to the mechanism of ion conductivity where the motions of ions are less dependent (decoupled) on segmental dynamics. We present that this phenomenon is observed in ionic materials as they approach their glass transition temperature and becomes essential for design and development of highly conducting solid polymer electrolytes. In this paper, we study the effect of chain rigidity on the decoupling of ion transport from segmental motion in three polymerized ionic liquids (polyILs) containing themore » same cation–anion pair but differing in flexibility of the polymer backbones and side groups. Analysis of dielectric and rheology data reveals that decoupling is strong in vinyl-based rigid polymers while almost negligible in novel siloxane-based flexible polyILs. To explain this behavior, we investigated ion and chain dynamics at ambient and elevated pressure. Our results suggest that decoupling has a direct relationship to the frustration in chain packing and free volume. Finally, these conclusions are also supported by coarse-grained molecular dynamics simulations.« less
  • Conductivity in polymer electrolytes has been generally discussed with the assumption that the segmental motions control charge transport. However, much less attention has been paid to the mechanism of ion conductivity where the motions of ions are less dependent (decoupled) on segmental dynamics. We present that this phenomenon is observed in ionic materials as they approach their glass transition temperature and becomes essential for design and development of highly conducting solid polymer electrolytes. In this paper, we study the effect of chain rigidity on the decoupling of ion transport from segmental motion in three polymerized ionic liquids (polyILs) containing themore » same cation–anion pair but differing in flexibility of the polymer backbones and side groups. Analysis of dielectric and rheology data reveals that decoupling is strong in vinyl-based rigid polymers while almost negligible in novel siloxane-based flexible polyILs. To explain this behavior, we investigated ion and chain dynamics at ambient and elevated pressure. Our results suggest that decoupling has a direct relationship to the frustration in chain packing and free volume. Finally, these conclusions are also supported by coarse-grained molecular dynamics simulations.« less
  • Polymerized ionic liquids (PolyILs) are promising candidates for energy storage and electrochemical devices applications. Understanding their ionic transport mechanism is the key for designing highly conductive PolyILs. By using broadband dielectric spectroscopy (BDS), rheology, and differential scanning calorimetry (DSC), a systematic study has been carried out to provide a better understanding of the ionic transport mechanism in PolyILs with different pendant groups. The variation of pendant groups results in different dielectric, mechanical, and thermal properties of these PolyILs. The Walden plot analysis shows that the data points for all these PolyILs fall above the ideal Walden line, and the deviationmore » from the ideal line increases upon approaching the glass transition temperature (T g). Moreover, the conductivity for these PolyILs at their Tgs are much higher than the usually reported value 10 15 S/cm for polymer electrolytes, in which the ionic transport is closely coupled to the segmental dynamics. These results indicate a decoupling of ionic conductivity from the segmental relaxation in these materials. The degree of decoupling increases with the increase of the fragility of polymer segmental relaxation. Finally, we relate this observation to a decrease in polymer packing efficiency with an increase in fragility.« less
  • The binary phase behavior of a series of imidazolium-based ionic liquids (ILs) has been investigated. In particular, the effect of two structural modifications of the imidazolium cation, alkyl chain length, and the introduction of a polymerizable acryloyl group at the alkyl chain terminus, has been studied using small angle X-ray scattering. Upon increasing water content, the non-polymerizable IL, 1-decyl-3-methylimidazolium chloride, adopts mesophase structures of predominately two-dimensional (2D) hexagonal symmetry, including structures intermediate in character between lamellae and 2D hexagonal micelles. Introduction of a photopolymerizable acryloyl functional group to form 1-(10-(acryloyloxy)decyl)-3-methylimidazolium chloride produces a rod-coil IL cation that yields self-assembled mesophasesmore » in which the formation of tetragonal morphologies is favored. Covalent linking of the IL cations by UV-induced polymerization converts the lyotropic mesophase into three-dimensional biocontinuous chemical gels. Reducing the alkyl chain length, as in the polymerizable IL cation 1-(8-(acryloyloxy)octyl)-3-methylimidazolium chloride, severely reduces the self-assembled mesophase order, and triggers the formation of only weakly ordered one-dimensional lamellar structures.« less