Pulsed-gradient spin-echo H-1 and F-19 NMR ionic diffusion coefficient, viscosity, and ionic conductivity of non-chloroaluminate room-temperature ionic liquids

Citation
A. Noda et al., Pulsed-gradient spin-echo H-1 and F-19 NMR ionic diffusion coefficient, viscosity, and ionic conductivity of non-chloroaluminate room-temperature ionic liquids, J PHYS CH B, 105(20), 2001, pp. 4603-4610
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
20
Year of publication
2001
Pages
4603 - 4610
Database
ISI
SICI code
1520-6106(20010524)105:20<4603:PSHAFN>2.0.ZU;2-N
Abstract
Room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluorobora te (EMIBF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-butylpyridinium tetrafluoroborate (BPBF4), and 1-butylpyridini um bis(trifluoromethylsulfonyl)imide (BPTFSI), were prepared and characteri zed. The thermal property, density, self-diffusion coefficient of the anion s and cations, viscosity, and ionic conductivity were measured for these io nic liquids in wide temperature ranges. A pulsed-gradient spin-echo NMR met hod was used to independently measure self-diffusion coefficients of the an ions (F-19 NMR) and the cations (H-1 NMR). The results indicate that the ca tions diffuse almost equally to the anion in EMIBF4 and BPBF4, whereas they diffuse faster than the anion in EMITFSI and BPTFSI. The summation of the cationic and anionic diffusion coefficients for each ionic liquid follows t he order EMITFSI > EMIBF4 > BPTFSI > BPBF4, under an isothermal condition. The order of the magnitude of the diffusion coefficient well contrasts with that of the viscosity for each ionic liquid. The temperature dependencies of the self-diffusion coefficient, viscosity, and ionic conductivity obey t he Vogel-Tamman-Fulcher (VTF) equation, and the VTF parameters were present ed. Relationships among the self-diffusion coefficient, viscosity, and mola r conductivity were analyzed in terms of the Stokes-Einstein equation and t he Nernst-Einstein equation. The most interesting feature of the relationsh ips is that the ratios of the molar conductivity, determined by complex imp edance measurements, to that calculated from the NMR diffusion coefficients , range from 0.6 to 0.8 for EMIBF4 and BPBF4, whereas the ratios range from 0.3 to 0.5 for EMITFSI and BPTFSI. This difference could be understood by taking the ionic association into consideration for EMITFSI and BPTFSI.