TY - JOUR
T1 - Structure and dynamics of ionic liquids
T2 - Trimethylsilylpropyl-substituted cations and bis(sulfonyl)amide anions
AU - Wu, Boning
AU - Yamashita, Yuki
AU - Endo, Takatsugu
AU - Takahashi, Kenji
AU - Castner, Edward W.
N1 - Funding Information:
This work is supported by the NSF through Grant No. CHE-1362272 to Rutgers University. Work in Kanazawa was supported in part by the Advanced Low Carbon Technology Research and Development Program (ALCA) (Grant No. 2100040), the Cross-ministerial Strategic Innovation Promotion Program (SIP), and the Center of Innovation Program Construction of next-generation infrastructure using innovative materials: Realization of safe and secure society that can coexist with the Earth for centuries from Japan Science and Technology Agency. High-energy X-ray experiments used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank APS beamline scientists, Dr. Olaf J. Borkiewicz, Kevin A. Beyer, and Dr. Karena W. Chapman for their assistance in X-ray data collection. The authors thank Mr. Yuki Matsushita, Kanazawa University, for previous preparation of the Si-IL samples. We thank Professor Claudio J. Margulis and Dr. Juan Carlos Araque from the University of Iowa for helpful suggestions and access to computational resources. We thank Dr. Nagarajan Murali at Rutgers University for the assistance with the PG-SE NMR experiments.
Publisher Copyright:
© 2016 Author(s).
PY - 2016/12/28
Y1 - 2016/12/28
N2 - Ionic liquids with cationic organosilicon groups have been shown to have a number of useful properties, including reduced viscosities relative to the homologous cations with hydrocarbon substituents on the cations. We report structural and dynamical properties of four ionic liquids having a trimethylsilylpropyl functional group, including 1-methyl-3-trimethylsilylpropylimidazolium (Si-C3-mim+) cation paired with three anions: bis(fluorosulfonyl)imide (FSI−), bis(trifluoromethanesulfonyl)imide (NTf2−), and bis(pentafluoroethanesulfonyl)imide (BETI−), as well as the analogous N-methyl-N-trimethylsilylpropylpyrrolidinium (Si-C3-pyrr+) cation paired with NTf2−. This choice of ionic liquids permits us to systematically study how increasing the size and hydrophobicity of the anions affects the structural and transport properties of the liquid. Structure factors for the ionic liquids were measured using high energy X-ray diffraction and calculated from molecular dynamics simulations. The liquid structure factors reveal first sharp diffraction peaks (FSDPs) for each of the four ionic liquids studied. Interestingly, the domain size for Si-C3-mim+/NTf2− indicated by the maxima for these peaks is larger than for the more polar ionic liquid with a similar chain length, 1-pentamethyldisiloxymethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (SiOSi-mim+/NTf2−). For the series of Si-C3-mim+ ionic liquids, as the size of the anion increases, the position of FSDP indicates that the intermediate range order domains decrease in size, contrary to expectation. Diffusivities for the anions and cations are compared for a series of both hydrocarbon-substituted and silicon-substituted cations. All of the anions show the same scaling with temperature, size, and viscosity, while the cations show two distinct trends - one for hydrocarbon-substituted cations and another for organosilicon-substituted cations, with the latter displaying increased friction.
AB - Ionic liquids with cationic organosilicon groups have been shown to have a number of useful properties, including reduced viscosities relative to the homologous cations with hydrocarbon substituents on the cations. We report structural and dynamical properties of four ionic liquids having a trimethylsilylpropyl functional group, including 1-methyl-3-trimethylsilylpropylimidazolium (Si-C3-mim+) cation paired with three anions: bis(fluorosulfonyl)imide (FSI−), bis(trifluoromethanesulfonyl)imide (NTf2−), and bis(pentafluoroethanesulfonyl)imide (BETI−), as well as the analogous N-methyl-N-trimethylsilylpropylpyrrolidinium (Si-C3-pyrr+) cation paired with NTf2−. This choice of ionic liquids permits us to systematically study how increasing the size and hydrophobicity of the anions affects the structural and transport properties of the liquid. Structure factors for the ionic liquids were measured using high energy X-ray diffraction and calculated from molecular dynamics simulations. The liquid structure factors reveal first sharp diffraction peaks (FSDPs) for each of the four ionic liquids studied. Interestingly, the domain size for Si-C3-mim+/NTf2− indicated by the maxima for these peaks is larger than for the more polar ionic liquid with a similar chain length, 1-pentamethyldisiloxymethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (SiOSi-mim+/NTf2−). For the series of Si-C3-mim+ ionic liquids, as the size of the anion increases, the position of FSDP indicates that the intermediate range order domains decrease in size, contrary to expectation. Diffusivities for the anions and cations are compared for a series of both hydrocarbon-substituted and silicon-substituted cations. All of the anions show the same scaling with temperature, size, and viscosity, while the cations show two distinct trends - one for hydrocarbon-substituted cations and another for organosilicon-substituted cations, with the latter displaying increased friction.
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U2 - 10.1063/1.4972410
DO - 10.1063/1.4972410
M3 - Article
AN - SCOPUS:85008883803
VL - 145
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 24
M1 - 244506
ER -