Self-diffusion, velocity cross-correlation, distinct diffusion and resistance coefficients of the ionic liquid [BMIM][Tf₂N] at high pressure

Abstract

Ion self-diffusion coefficients (DSi) have been measured for the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BMIM][Tf2N] at pressures to 200 MPa between 25 and 75 °C and at 0.1 MPa between 10 and 90 °C. Self-diffusion coefficients are reported for 1-ethyl-, 1-hexyl- and 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide salts at 0.1 MPa, supplemented by viscosity, electrical conductivity and density measurements. Velocity cross-correlation (VCC, fij) and distinct diffusion coefficients (D) are calculated from the data. Both DSi and D are analysed in terms of (fractional) Stokes-Einstein-Sutherland (SES) equations. SES and Walden plots show almost identical slopes, with high-pressure isotherms and the atmospheric pressure isobar falling on common, single lines for each property for [BMIM][Tf2N]. SES plots for the anion self-diffusion coefficients for the [RMIM][Tf2N] (R = alkyl) series are coincident, whereas those for the cations depend on their alkyl substitution, as do the Walden plots. In common with other [Tf2N](-) salts, the VCC follow the order f-- < f++ < f+-. The Nernst-Einstein deviation parameter Δ for [BMIM][Tf2N] is independent of temperature and pressure. Those for the other [Tf2N](-) salts are independent of temperature. Δ increases in magnitude with increasing alkyl chain length on the cation. The transport properties of [BMIM][Tf2N] are re-examined in terms of density scaling using reduced conductivities and reduced molar conductivities for the first time. Identical scaling parameters (γ) are obtained for the several reduced transport properties. This result is supported by data for other ionic liquids. It is suggested that the γ for ionic liquids may depend on packing fraction.

Self-Diffusion Coefficients and Related Transport Properties for a Number of Fragile Ionic Liquids

“…77 Note that the r ii can be the difference between much larger terms, so the uncertainties can be somewhat greater than for the corresponding VCC. 5 We have found that the r ij increase with increasing viscosity, decreasing temperature, increasing pressure, and decreasing cation size for salts of the same anion. 5 The condition Table 6.…”

“…5 We have found that the r ij increase with increasing viscosity, decreasing temperature, increasing pressure, and decreasing cation size for salts of the same anion. 5 The condition Table 6. The higher conductivity for [EMIM][FAP] reflects the observation that the Nernst−Einstein deviation parameter, Δ, ∼ 0 for this salt (see Figure 7).…”

“…[2][3][4][5]9,21,22,24 This applied to mainly 1-methyl-3-alkylimidazolium salts, with n-butyl, n-hexyl, and noctyl side groups, but also N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ( (Figures 3 and 4). The data did not show any sharp discontinuity, but could not be fitted by eq 9, even when the exponent of T was not fixed.…”

“…In the examples studied to date, 2−5,9 |f +− | < |f ++ |, |f −− |; that is, the anticorrelation is smallest for the unlike ion interactions, and |f ++ | > |f −− |for [BF 4 ] − and [PF 6 ] − salts of 1-alkyl-3-methylimidazolium ions, 2,3 but |f ++ | < |f −− |for [Tf 2 N] − salts containing a range of cations with different structures. 4,5,9,16 The work described above has been summarized at a recent Faraday Discussion. 1 In that work, we also gave a preliminary report on what appeared to be a "dynamic crossover effect" in the viscosity and conductivity of SO 3 ].…”

Communication: Studies of the Lennard-Jones fluid in 2, 3, and 4 dimensions highlight the need for a liquid-state 1/d expansion

“…27 from 2014. After that paper was written, it became clear that Roskilde (R) simple systems [29][30][31][32][33][34][35][36][37][38][39][40][41][42] -those with R > 0.9-are characterized by approximately obeying the following condition:…”