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Title: Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies

Abstract

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 the 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.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [1];  [2]; ORCiD logo [4];  [2];  [1]; ORCiD logo [1]; ORCiD logo [2];  [5]; ORCiD logo [6];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  2. Univ. of Tennessee, Knoxville, TN (United States). Department of Chemistry
  3. Univ. of Cincinnati, OH (United States). Department of Aerospace Engineering & Engineering Mechanics
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences and Computational Sciences & Engineering Division
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Univ. of Tennessee, Knoxville, TN (United States). Department of Chemistry
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Univ. of Tennessee, Knoxville, TN (United States). Department of Chemistry and Department of Physics and Astronomy
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1408579
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 50; Journal Issue: 17; 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

Wojnarowska, Zaneta, Feng, Hongbo, Fu, Yao, Cheng, Shiwang, Carroll, Bobby, Kumar, Rajeev, Novikov, Vladimir N., Kisliuk, Alexander M., Saito, Tomonori, Kang, Nam-Goo, Mays, Jimmy W., Sokolov, Alexei P., and Bocharova, Vera. Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies. United States: N. p., 2017. Web. doi:10.1021/acs.macromol.7b01217.
Wojnarowska, Zaneta, Feng, Hongbo, Fu, Yao, Cheng, Shiwang, Carroll, Bobby, Kumar, Rajeev, Novikov, Vladimir N., Kisliuk, Alexander M., Saito, Tomonori, Kang, Nam-Goo, Mays, Jimmy W., Sokolov, Alexei P., & Bocharova, Vera. Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies. United States. doi:10.1021/acs.macromol.7b01217.
Wojnarowska, Zaneta, Feng, Hongbo, Fu, Yao, Cheng, Shiwang, Carroll, Bobby, Kumar, Rajeev, Novikov, Vladimir N., Kisliuk, Alexander M., Saito, Tomonori, Kang, Nam-Goo, Mays, Jimmy W., Sokolov, Alexei P., and Bocharova, Vera. 2017. "Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies". United States. doi:10.1021/acs.macromol.7b01217.
@article{osti_1408579,
title = {Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies},
author = {Wojnarowska, Zaneta and Feng, Hongbo and Fu, Yao and Cheng, Shiwang and Carroll, Bobby and Kumar, Rajeev and Novikov, Vladimir N. and Kisliuk, Alexander M. and Saito, Tomonori and Kang, Nam-Goo and Mays, Jimmy W. and Sokolov, Alexei P. and Bocharova, Vera},
abstractNote = {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 the 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.},
doi = {10.1021/acs.macromol.7b01217},
journal = {Macromolecules},
number = 17,
volume = 50,
place = {United States},
year = 2017,
month = 8
}

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  • We present detailed studies of the relationship between ionic conductivity and segmental relaxation in polymer electrolytes. The analysis shows that the ionic conductivity can be decoupled from segmental dynamics and the strength of the decoupling correlates with the fragility but not with the glass transition temperature. These results call for a revision of the current picture of ionic transport in polymer electrolytes. We relate the observed decoupling phenomenon to frustration in packing of rigid polymers, where the loose local structure is also responsible for the increase in their fragility.
  • 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
  • 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
  • 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,more » 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.« less