Transport Properties of the 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide–Trichloromethane Binary System: Indication of Trichloromethane Segregation

Saeva, David R.; Petenuci, João; Hoffmann, Markus M.

doi:10.1021/acs.jpcb.6b06974

Cited by 5 publications

(6 citation statements)

References 102 publications

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“…A similar observation of a maximum of r has recently been observed for the aggregation behavior of several imidazolium based ionic liquids in solvents of low polarity. − The maximum has been interpreted with a change in the transport mechanism. − Specifically, at low concentrations, mass transport is reflected by the movement of individual solute molecules and aggregates, while at high concentrations the movement by the large aggregates becomes negligibly small and mass transport is dominated by individual molecules and small aggregates moving from large aggregate to large aggregate. This viewpoint can be further illustrated considering that D C10E6 is the mole fraction weighted average of the self-diffusion coefficient of each present C 10 E 6 species as expressed in eq for the simplifying case of considering only unaggregated C 10 E 6 ( x free ) and aggregated C 10 E 6 ( x agg ): Using eq , eq can be re-expressed in terms of corresponding species radii as shown in eq . From eq , it can be seen that, as long as there is a significant concentration of unaggregated C 10 E 6 , the “free” C 10 E 6 term in eq will dominate for r agg ≫ r free .…”

Section: Resultssupporting

confidence: 63%

“…Unreasonably small solvent radii were also noted for the analysis of the aggregation behavior of an imidazolium based ionic liquid in chloroform by eq . This observation of unreasonably small solvent radii led us to attempt an evaluation of the average C 10 E 6 speciation radii using the self-diffusion coefficient of the cyclohexane as the internal standard with known radius of 2.90 Å according to eq . …”

Section: Resultsmentioning

confidence: 99%

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Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Hoffmann

Bothe²,

Gutmann³

et al. 2018

J. Phys. Chem. B

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The colligative property freezing point depression is evaluated as a means for estimating the extent of aggregation for solutions of poly(ethylene oxide) alcohol (CE) nonionic surfactant in cyclohexane. Combined with additional measurements of self-diffusion coefficients, it is shown that both unaggregated CE as well as reverse micelles are significantly present for the entire range of measured CE concentration (0.048-2.35 mol kg). A change in speciation near 0.2 mol kg is indicated by the results from both freezing point depression and self-diffusion coefficient measurements. It is shown that average reverse micelle radii and aggregation numbers obtained from the ratio of solvent and CE self-diffusion coefficients are consistent with prior reported results. However, unreasonably small radii for the reverse micelles as well as for the cyclohexane were obtained from analysis of the results by the Stokes-Einstein equation using additional measured solution viscosities. The concentration of reverse micelles and unaggregated CE was calculated from the freezing point depression results using the aggregation numbers obtained from ratio of self-diffusion coefficients. These concentrations indicate that the reverse micelles become smaller in average size and increase in number with increasing temperature without an increase in unaggregated CE.

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Section: Resultssupporting

confidence: 63%

Section: Resultsmentioning

confidence: 99%

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Hoffmann

Bothe²,

Gutmann³

et al. 2018

J. Phys. Chem. B

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“…However, it should be noted that other systems in the literature seem to deviate from Stokes-Einstein behavior. Hoffmann and coworkers measured the viscosity and diffusivity of [HMIm][Tf 2 N] and chloroform [73,74].…”

Section: Diffusivity Of [Hmim][tf 2 N] Saturated With Compressed R-13mentioning

confidence: 99%

Viscosity and self-diffusivity of ionic liquids with compressed hydrofluorocarbons: 1-Hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide and 1,1,1,2-tetrafluoroethane

Ahosseini

Wei

Weatherley

et al. 2017

Fluid Phase Equilibria

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The viscosity and self-diffusivity of mixtures of the ionic liquid, 1-hexyl-3methylimidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf 2 N]), and the compressed gas, 1,1,1,2-tetrafluoroethane (R-134a), were measured at three different temperatures (298.15 K, 323.15 K, 343.15 K) and pressures to 21 bar. The high-pressure vapor-liquid equilibrium (VLE) of the ionic liquids with R-134a was measured to calculate the composition of the liquid phase at the various pressures encountered in the viscosity and diffusivity measurements. The viscosity of the ionic liquid decreases significantly with increased composition of R-134a at VLE. The "excess" viscosity demonstrates positive values that are believed to represent relatively strong intermolecular forces of the polar R-134a and [HMIm][Tf 2 N]. The self-diffusivity of mixtures of [HMIm][Tf 2 N] and liquefied R-134a (298.15 K and 6.7 bar) was measured and increases significantly with increases in the composition of R-134a. The selfdiffusivity of [HMIm][Tf 2 N] in vapor-liquid equilibrium with compressed R-134a gas was measured and indicates similar increases in diffusivity with composition of R-134a. The diffusivity demonstrates close Stokes-Einstein behavior using the measured mixture viscosity data and ambient pressure self-diffusivity.

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“…Figure 22. Comparison of ion dissociation of [C 6 mim][Tf 2 N] in chloroform (CHCl 3 ) at 288.2 K (▲, red), 298.2K ( ◆ , blue), and 318.2 K ( ■ , green) calculated using the Stokes−Einstein approximation and PFG-NMR values (△, ◇ , □ ) from Hoffman et al197 …”

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confidence: 99%

Ion Dissociation in Ionic Liquids and Ionic Liquid Solutions

2020

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The extent to which cations and anions in ionic liquids (ILs) and ionic liquid solutions are dissociated is of both fundamental scientific interest and practical importance because ion dissociation has been shown to impact viscosity, density, surface tension, volatility, solubility, chemical reactivity, and many other important chemical and physical properties. When mixed with solvents, ionic liquids provide the unique opportunity to investigate ion dissociation from infinite dilution in the solvent to a completely solvent-free state, even at ambient conditions. The most common way to estimate ion dissociation in ILs and IL solutions is by comparing the molar conductivity determined from ionic conductivity measurements such as electrochemical impedance spectroscopy (EIS) (which measure the movement of only the charged, i.e., dissociated, ions) with the molar conductivity calculated from ion diffusivities measured by pulse field gradient nuclear magnetic resonance spectroscopy (PFG-NMR, which gives movement of all of the ions). Because the NMR measurements are time-consuming, the number of ILs and IL solutions investigated by this method is relatively limited. We have shown that use of the Stokes–Einstein equation with estimates of the effective ion Stokes radii allows ion dissociation to be calculated from easily measured density, viscosity, and ionic conductivity data (ρ, η, λ), which is readily available in the literature for a much larger number of pure ILs and IL solutions. Therefore, in this review, we present values of ion dissociation for ILs and IL solutions (aqueous and nonaqueous) determined by both the traditional molar conductivity/PFG-NMR method and the ρ, η, λ method. We explore the effect of cation and anion alkyl chain length, structure, and interaction motifs of the cation and anion, temperature, and the strength of the solvent in IL solutions.

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Transport Properties of the 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide–Trichloromethane Binary System: Indication of Trichloromethane Segregation

Cited by 5 publications

References 102 publications

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Viscosity and self-diffusivity of ionic liquids with compressed hydrofluorocarbons: 1-Hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide and 1,1,1,2-tetrafluoroethane

Ion Dissociation in Ionic Liquids and Ionic Liquid Solutions

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