Decoupling charge transport from the structural dynamics in room temperature ionic liquids

Philip Griffin; Alexander L. Agapov; Alexander Kisliuk; Xiao Guang Sun; Sheng Dai; Vladimir N. Novikov; Alexei P. Sokolov

doi:10.1063/1.3638269

Decoupling charge transport from the structural dynamics in room temperature ionic liquids

Philip Griffin, Alexander L. Agapov, Alexander Kisliuk, Xiao Guang Sun, Sheng Dai, Vladimir N. Novikov, Alexei P. Sokolov

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66 Scopus citations

Abstract

Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) C4mimNTf2 in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward T_g. The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in C4mimNTf2 to be T_c ∼ 225 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.

Original language	English
Article number	114509
Journal	Journal of Chemical Physics
Volume	135
Issue number	11
DOIs	https://doi.org/10.1063/1.3638269
State	Published - Sep 21 2011

Funding

P.G. thanks National Science Foundation (NSF) for the financial support (Grant No. DMR-1059562). A.P.S., A.K., X.G.S., and S.D. acknowledge the support from the Division of Materials Sciences and Engineering, (U.S.) Department of Energy (DOE) Office of Basic Energy Sciences, and V.N.N. acknowledges the financial support from the LDRD Program (LOIS 5843) of ORNL, managed by UT-Battelle, LLC for DOE, and from the Russian Federation for Basic Research (RFBR) (Grant No. 09-02-01297a).

Funders	Funder number
National Science Foundation	DMR-1059562
Basic Energy Sciences
Oak Ridge National Laboratory
Laboratory Directed Research and Development
Division of Materials Sciences and Engineering
Russian Foundation for Basic Research	09-02-01297a

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title = "Decoupling charge transport from the structural dynamics in room temperature ionic liquids",

abstract = "Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) C4mimNTf2 in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward Tg. The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in C4mimNTf2 to be Tc ∼ 225 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.",

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AU - Griffin, Philip

AU - Agapov, Alexander L.

AU - Kisliuk, Alexander

AU - Sun, Xiao Guang

AU - Dai, Sheng

AU - Novikov, Vladimir N.

AU - Sokolov, Alexei P.

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N2 - Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) C4mimNTf2 in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward Tg. The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in C4mimNTf2 to be Tc ∼ 225 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.

AB - Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) C4mimNTf2 in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward Tg. The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in C4mimNTf2 to be Tc ∼ 225 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.

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Decoupling charge transport from the structural dynamics in room temperature ionic liquids

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