Transport Properties of N-Butyl-N-methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide

The viscosities (η) and ion self-diffusion coefficients ( D i ) of the ionic liquid N -butyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Pyr 14 ][Tf 2 N] or [C 4 mpyr][Tf 2 N]) are reported between (0 and 90) °C and at pressures to 103 MPa and between (25 and 80) °C to 250 MPa, respectively. A falling-body high-pressure viscometer was employed, supplemented by a Stabinger rotating-cylinder viscometer for atmospheric pressure. Self-diffusion coefficients were measured by the steady-gradient spin–echo NMR technique. The overall uncertainties are ± 2 % and ± 3 %, respectively. Conductivities (κ) and densities obtained between (0 and 90) °C at 0.1 MPa are reported. Ion self-diffusion coefficients and densities at 0.1 MPa are included for N -methyl- N -propyl-3-azabicyclo[3.2.2]nonaneium bis(trifluoromethylsulfonyl)amide ([3-ABN 13 ][Tf 2 N]). The transport properties are examined using the fractional Stokes–Einstein and Nernst–Einstein relations, velocity correlation coefficients, and density scaling. For [Pyr 14 ][Tf 2 N], the fractional Stokes–Einstein exponents are (0.93 ± 0.05). There is very good consistency between the diffusion and molar conductivity (Λ) data, with a slope of (0.99 ± 0.05) for a plot of ln( TΛ ) against ln( D + + D – ). The Nernst–Einstein deviation parameter, Δ, is (0.313 ± 0.013): it is consistent with the relation f +- > ( f ++ + f –- )/2 for the ion–ion velocity cross-correlation coefficients, f ij . Density scaling to the temperature-volume function ( TV γ ) has been applied to both unreduced and reduced viscosities and self-diffusion coefficients for [Pyr 14 ][Tf 2 N]. Consistent scaling parameters γ are obtained for each of η, D +, and D – with both the Casalini-Roland model and a simple polynomial fit in ( TV γ ), and for the reduced quantities, η̃, D̃ +, and D̃ – . At a fixed temperature, the self-diffusion coefficients for the series [BMIM][Tf 2 N], [Pyr 14 ][Tf 2 N], and [3-ABN 13 ][Tf 2 N] decrease with increasing salt molar volume, but the ratio of D (cation) to D (anion) changes from values greater than unity to less than unity, in common with what is generally observed for ionic liquid families.