Resiliency among United States Air Force personnel: The direct and interactive influence of cognitive fitness and confidence in social connections.

The United States (U.S.) military has focused on increasing service members' (SM) mental and social fitness to bolster resiliency (successful role performance). The Resiliency Model of Role Performance posits that individual assets and social connections account for SM's differential success in meeting military demands and personal obligations. We used a U.S. Air Force (AF) active-duty dataset to test for a direct, positive relationship between cognitive fitness and both formal and informal social connections, and the impact on successful role performance. We also tested for potential moderating influences of formal and informal social connections on role performance among SMs with low vs. high cognitive fitness. Data were collected from a non-probability purposive sample of AF SMs and civilians (N = 59,094) who completed the Support and Resiliency Inventory between November 4, 2011 and January 7, 2014. We focused on the married active-duty subsample (n = 29,387). We employed multivariate hierarchical regression analysis across three models to explore the direct and interactive influence of cognitive and social fitness on resiliency. Controlling for military demographic characteristics, we found a positive linear relationship between cognitive fitness and resiliency and between informal and formal support and resiliency. Informal social support moderated the association between cognitive fitness and resiliency, compensating for resiliency among SMs with lower cognitive fitness. Study findings support current military resilience-building initiatives and underline the importance of prioritizing informal social support in U.S. military settings.

Does [Tf2N]- slither? Equivalence of cation and anion self-diffusion activation volumes in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

New high-pressure self-diffusion data are reported for the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][Tf2N]) at pressures up to 363 MPa in the temperature range 288-348 K. The cation and anion activation volumes derived from these are found to be equal at a fixed temperature, within experimental error, in contradiction to a report in the literature that they differ significantly. Self-diffusion activation volumes derived from our earlier high-pressure diffusion studies also show equality for the respective cations and anions of bis(trifluoromethylsulfonyl)amide, tetrafluoroborate and hexafluorophosphate salts with various cations. Stokes-Einstein-Sutherland analysis and density scaling are applied to the [EMIM][Tf2N] self-diffusion measurements and support the conclusion that pressure effects both cation and anion mass (and hence charge) transport in the same way. The density scaling parameters are consistent with the theoretical predictions of Knudsen et al. and agree with that for the viscosity, as for other ionic liquids.

A volumetric and intra-diffusion study of solutions of AlCl3 in two ionic liquids - [C2TMEDA][Tf2N] and [C4mpyr][Tf2N].

Intra-diffusion coefficients (DSi) have been measured for the ionic liquid constituent ions and aluminium-containing species in aluminium chloride (AlCl3) solutions in the ionic liquids 1-(2-dimethyl-aminoethyl)-dimethylethylammonium bis(trifluoromethylsulfonyl)amide ([C2TMEDA][Tf2N]) and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([C4mpyr][Tf2N]), to investigate whether spectroscopically detected interactions between the ions and AlCl3 affect these properties. Such electrolyte solutions are of interest for the electrowinning of aluminium. The temperature, composition and molar volume dependences are investigated. Apparent (Vϕ,1) and partial molar (V1) volumes for AlCl3 have been calculated from solution densities. For [C2TMEDA][Tf2N] solutions, Vϕ,1 increases with increasing solute concentration; for [C4mpyr][Tf2N] solutions, it decreases. In pure [C2TMEDA][Tf2N], the cation diffuses more quickly than the anion, but this changes as the AlCl3 concentration increases. In the [C4mpyr][Tf2N] solutions, the intra-diffusion coefficient ratio remains equal to that for the pure ionic liquid and the aluminium species diffuses at approximately the same rate as the anion at each composition. The intra-diffusion coefficients can be fitted to the Ertl-Dullien free volume power law by superposing the iso-concentration curves with concentration dependent, but temperature independent, molar volume offsets. This suggests that they are primarily dependent on the molar volume and secondarily on a colligative thermodynamic factor due to dilution by AlCl3. AlCl3 complexation by [Tf2N]- and [C2TMEDA]+, confirmed by 27Al, 15N and 19F NMR spectroscopy, seems to play a minor role. Our results indicate that the application of free volume theories might be fruitful in the study of the transport properties of ionic liquid solutions and mixtures.

Thermodynamic or density scaling of the electrical conductivity of molten salts.

Thermodynamic or density scaling of high-pressure conductivities and molar conductivities of the high-temperature molten salts NaOH, and the alkali chlorides, bromides, and nitrates, from Na to Cs, taken from the literature, is found to be consistent with the simulations of Knudsen, Niss, and Bailey (KNB). They used a simple model fluid of point particles interacting through an interionic potential with a repulsive inverse power law part varying as r-9 and an attractive Coulombic part. This yields values between the limits 0.33-3 for the scaling parameter, γ. The Coulombic potential reduces the scaling parameter to values much lower than are normally found for molecular liquids, and KNB used this to explain the low values typically found for ionic liquids. Here, it is shown that the high-temperature molten salts examined behave similarly.

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

Correction for 'Self-diffusion, velocity cross-correlation, distinct diffusion and resistance coefficients of the ionic liquid [BMIM][Tf2N] at high pressure' by Kenneth R. Harris et al., Phys. Chem. Chem. Phys., 2015, 17, 23977-23993, DOI: 10.1039/C5CP04277A.

Thermodynamic or density scaling of the thermal conductivity of liquids.

Thermodynamic or density scaling is applied to thermal conductivity (λ) data from the literature for the model Lennard-Jones (12-6) fluid; the noble gases neon to xenon; nitrogen, ethene, and carbon dioxide as examples of linear molecules; the quasi-spherical molecules methane and carbon tetrachloride; the flexible chain molecules n-hexane and n-octane; the planar toluene and m-xylene; the cyclic methylcyclohexane; the polar R132a and chlorobenzene; and ammonia and methanol as H-bonded fluids. Only data expressed as Rosenfeld reduced properties could be scaled successfully. Two different methods were used to obtain the scaling parameter γ, one based on polynomial fits to the group (TVγ) and the other based on the Avramov equation. The two methods agree well, except for λ of CCl4. γ for the thermal conductivity is similar to those for the viscosity and self-diffusion coefficient for the smaller molecules. It is significantly larger for the Lennard-Jones fluid, possibly due to a different dependence on packing fraction, and much larger for polyatomic molecules where heat transfer through internal modes may have an additional effect. Methanol and ammonia, where energy can be transmitted through intermolecular hydrogen bonding, could not be scaled. This work is intended as a practical attempt to examine thermodynamic scaling of the thermal conductivity of real fluids. The divergence of the scaling parameters for different properties is unexpected, suggesting that refinement of theory is required to rationalize this result. For the Lennard-Jones fluid, the Ohtori-Iishi version of the Stokes-Einstein-Sutherland relation applies at high densities in the liquid and supercritical region.

Correction: Comment on "Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?" by M. Gouverneur, F. Schmidt and M. Schönhoff, Phys. Chem. Chem. Phys., 2018, 20, 7470.

Correction for 'Comment on "Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?" by M. Gouverneur, F. Schmidt and M. Schönhoff, Phys. Chem. Chem. Phys., 2018, 20, 7470' by Kenneth R. Harris, Phys. Chem. Chem. Phys., 2018, 20, 30041-30045.

Comment on "Negative effective Li transference numbers in Li salt/ionic liquid mixtures: does Li drift in the "Wrong" direction?" by M. Gouverneur, F. Schmidt and M. Schönhoff, Phys. Chem. Chem. Phys., 2018, 20, 7470.

Gouverneur et al. have recently reported "effective transport numbers" for mixtures of lithium and 1-ethyl-3-methylimidazolium salts with common (fluorinated) anions using 7Li, 1H and 19F and electrophoretic NMR to determine the electrophoretic mobilities of all three ionic species. The "effective transport number" for lithium is small, but negative. From this they deduce that the Li+ ions are each associated with two or more anions to form negatively charged complexes. However this interpretation may be incorrect: only a single independent transport number can be measured in such a system as the three ion fluxes are not independent. One ion flow must define the reference frame and then the transport numbers for the other two ions must sum to unity. Electrophoretic NMR appears to produce what are called "external" ion mobilities and transport numbers in the notation used by Klemm and Haase for molten salts. These are defined in the laboratory frame of reference and can depend on the boundary conditions of the experiment. Simple relations exist for their conversion to "internal" transport numbers where ion mobilities for two ions are given relative to that of the third, analogous to the more familiar Hittorf transport numbers of ions in electrolyte solutions which are given in the "solvent-fixed" frame of reference, i.e. relative to the flow of solvent. It is not unusual for a cation external transport number to be negative in molten salt mixtures, e.g. (LiNO3 + AgNO3) in a Hittorf experiment employing nitrate electrodes whereas true ion association would produce negative internal transport numbers. In the examples studied by Gouverneur et al. the cation internal transport numbers are both positive. Those for Li+ are also very small, and close to zero within experimental error. This may simply reflect that the mixtures employed are dilute in lithium ions.

The importance of transport property studies for battery electrolytes: revisiting the transport properties of lithium-N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide mixtures.

Transport properties are examined in some detail for samples of the low temperature molten salt N-propyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide [Pyr13][FSI] from two different commercial suppliers. A similar set of data is presented for two different concentrations of binary lithium-[Pyr13][FSI] salt mixtures from one supplier. A new and significantly different production process is used for the synthesis of Li[FSI] as well as the [Pyr13]+ salt used in the mixtures. Results for the viscosity, conductivity, and self-diffusion coefficients, together with the density and expansivity and apparent molar volume, are reported over the temperature range of (0 to 80) °C. The data for neat [Pyr13][FSI] are discussed in the context of velocity cross correlation (VCC or fij) and Laity resistance (rij) coefficients. Unusually, f+- ∼ f++ < f--. The three resistance coefficients are of similar magnitude indicating all three ion-ion interactions contribute to the transport properties, not just the cation-anion interaction. The composition dependence of the transport properties is compared to previously reported data for the same and related compounds: in contrast to high-temperature molten salt mixtures, this is an exponential dependence. The Nernst-Einstein parameter Δ, which contains information on the correlations of the ionic velocities and is determined by differences in the VCC for the various ion-ion combinations, was calculated for both the neat ionic liquid and its binary mixture. It increases with increasing lithium concentration. The new data set also allows some conclusions with regards to the lithium-[FSI]- coordination environment.

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

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.

Viscosity scaling of the self-diffusion and velocity cross-correlation coefficients of two functionalised ionic liquids and of their non-functionalized analogues.

Ion self-diffusion coefficients have been measured for ionic liquids based on the cations N-acetoxyethyl-N,N-dimethyl-N-ethylammonium ([N(112,2OCO1)](+)) and its non-functionalised analogue, N,N-dimethyl-N-ethyl-N-pentylammonium ([N1125](+)), and N,N-dimethyl-N-ethyl-N-methoxyethoxyethylammonium ([N(112,2O2O1)](+)), and its analogue, N,N-dimethyl-N-ethyl-N-heptylammonium ([N1127](+)) and the bis(trifluoromethanesulfonyl)amide anion. The functionalised chain on an ammonium cation has the same length, in terms of the number of atoms, as the non-functionalised chain of the corresponding analogue. For [N(112,2OCO1)][Tf2N] and [N1127][Tf2N], the cation and anion self-diffusion coefficients are equal, within experimental error, whereas for [N1125][Tf2N], the cation diffuses more quickly, and for [N(112,2O2O1)][Tf2N], it is the anion that diffuses more quickly than the ether-functionalised cation. But these differences are relatively small, just beyond experimental error. The data are used to calculate velocity cross-correlation coefficients (VCC or f(ij)) and distinct diffusion coefficients (D(ij)(d)). Both the self-diffusion and distinct diffusion coefficients are analysed in terms of (fractional) Stokes-Einstein-Sutherland equations. Though the self-diffusion coefficients, as with the conductivity and viscosity, show marked differences in absolute terms between the functionalised and non-functionalised forms, being higher for the ethoxy-substituted IL and lower for the acetoxy-substituted IL, these are largely removed by scaling with the viscosity. Thus the transport properties are better understood as functions of the viscosity rather than the temperature and density, per se. The presence of the alkoxy-substituted side chains is known to change the local mesoscopic liquid structure, but it appears once this is done, the transport properties scale correspondingly. In the case of the acetoxy-substituted IL, this is also largely the case, but the Nernst-Einstein deviation parameter, Δ, which depends on the difference between the anion-cation VCC and the mean of the cation-cation and anion-anion VCCs, is smaller than that of its analogue salt, and also temperature dependent.

Effect of Relative Mass on Ion Velocity Cross-Correlations in Ionic Liquids and Molten Salts: Different Perspectives in Different Reference Frames.

In electrolytes, the self- and interdiffusion coefficients, transport numbers, and electrical conductivity can be used to determine velocity cross-correlation coefficients (VCC) that are also accessible through molecular dynamics simulations. In an ionic liquid or molten salt, there are only three, corresponding to correlations between the velocities of distinct ion pairs (cation-anion, cation-cation, and anion-anion) averaged over both the ensemble and time, calculable from experimental ion self-diffusion coefficients and the electrolyte conductivity. Most usually, the mass-fixed frame of reference (with velocities relative to that of the center of mass of the system) is used to discuss the VCC and the distinct diffusion coefficients (DDC) derived from them. Recent work in the literature has suggested a dependence of the DDC on the ratio of the anion to cation mass. Here, we demonstrate, using our own and literature transport property data for a large number of ionic liquids and molten salts, that the trends observed depend on the particular choice of velocity reference frame, mass-, number-, or volume-fixed. The perception of ion-ion interactions may be distorted in the mass- and volume fixed frames when the co-ions have very different masses or volumes, particularly for systems containing light lithium ions.

Transport, electrochemical and thermophysical properties of two N-donor-functionalised ionic liquids.

Two N-donor-functionalised ionic liquids (ILs), 1-ethyl-1,4-dimethylpiperazinium bis(trifluoromethylsulfonyl)amide (1) and 1-(2-dimethylaminoethyl)-dimethylethylammonium bis(trifluoromethylsulfonyl)amide (2), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (3). Marked differences in thermal and electrochemical stability were observed between the two tertiary-amine-functionalised salts and the non-functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self-diffusion coefficients (Di ) and molar conductivities (Λ) are higher for the IL with an open-chain cation (2) than that with a cyclic cation (1), but less than that with a non-functionalised, heterocyclic cation (3). The viscosities (η) show the opposite behaviour. The Walden [Λ[proportionality](1/η)(t) ] and Stokes-Einstein [Di /T)[proportionality](1/η)(t) ] exponents, t, are very similar for the three salts, 0.93-0.98 (±0.05); that is, the self-diffusion coefficients and conductivity are set by η. The Di for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13% higher than that of 2. The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D+ +D- ). The Nernst-Einstein deviation parameters (Δ) are such that the mean of the two like-ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3, 1 and 2, respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order D(d)__ < D(d)++ < D(d)+_, as is common for [Tf2N](-) salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti-correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti-correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t~0.95.

On the density scaling of pVT data and transport properties for molecular and ionic liquids.

In this work, a general equation of state (EOS) recently derived by Grzybowski et al. [Phys. Rev. E 83, 041505 (2011)] is applied to 51 molecular and ionic liquids in order to perform density scaling of pVT data employing the scaling exponent γ(EOS). It is found that the scaling is excellent in most cases examined. γ(EOS) values range from 6.1 for ammonia to 13.3 for the ionic liquid [C(4)C(1)im][BF(4)]. These γ(EOS) values are compared with results recently reported by us [E. R. López, A. S. Pensado, M. J. P. Comuñas, A. A. H. Pádua, J. Fernández, and K. R. Harris, J. Chem. Phys. 134, 144507 (2011)] for the scaling exponent γ obtained for several different transport properties, namely, the viscosity, self-diffusion coefficient, and electrical conductivity. For the majority of the compounds examined, γ(EOS) > γ, but for hexane, heptane, octane, cyclopentane, cyclohexane, CCl(4), dimethyl carbonate, m-xylene, and decalin, γ(EOS) < γ. In addition, we find that the γ(EOS) values are very much higher than those of γ for alcohols, pentaerythritol esters, and ionic liquids. For viscosities and the self-diffusion coefficient-temperature ratio, we have tested the relation linking EOS and dynamic scaling parameters, proposed by Paluch et al. [J. Phys. Chem. Lett. 1, 987-992 (2010)] and Grzybowski et al. [J. Chem. Phys. 133, 161101 (2010); Phys. Rev. E 82, 013501 (2010)], that is, γ = (γ(EOS)/φ) + γ(G), where φ is the stretching parameter of the modified Avramov relation for the density scaling of a transport property, and γ(G) is the Grüneisen constant. This relationship is based on data for structural relaxation times near the glass transition temperature for seven molecular liquids, including glass formers, and a single ionic liquid. For all the compounds examined in our much larger database the ratio (γ(EOS)/φ) is actually higher than γ, with the only exceptions of propylene carbonate and 1-methylnaphthalene. Therefore, it seems the relation proposed by Paluch et al. applies only in certain cases, and is really not generally applicable to liquid transport properties such as viscosities, self-diffusion coefficients or electrical conductivities when examined over broad ranges of temperature and pressure.

Density scaling of the transport properties of molecular and ionic liquids.

Casalini and Roland [Phys. Rev. E 69, 062501 (2004); J. Non-Cryst. Solids 353, 3936 (2007)] and other authors have found that both the dielectric relaxation times and the viscosity, η, of liquids can be expressed solely as functions of the group (TV (γ)), where T is the temperature, V is the molar volume, and γ a state-independent scaling exponent. Here we report scaling exponents γ, for the viscosities of 46 compounds, including 11 ionic liquids. A generalization of this thermodynamic scaling to other transport properties, namely, the self-diffusion coefficients for ionic and molecular liquids and the electrical conductivity for ionic liquids is examined. Scaling exponents, γ, for the electrical conductivities of six ionic liquids for which viscosity data are available, are found to be quite close to those obtained from viscosities. Using the scaling exponents obtained from viscosities it was possible to correlate molar conductivity over broad ranges of temperature and pressure. However, application of the same procedures to the self-diffusion coefficients, D, of six ionic and 13 molecular liquids leads to superpositioning of poorer quality, as the scaling yields different exponents from those obtained with viscosities and, in the case of the ionic liquids, slightly different values for the anion and the cation. This situation can be improved by using the ratio (D∕T), consistent with the Stokes-Einstein relation, yielding γ values closer to those of viscosity.

A lattice-hole theory for conductivity in ionic liquid mixtures: application to ionic liquid + water mixtures.

We derive a new expression for the conductivity of ionic liquid-solvent mixtures. The underlying theory is based on a lattice-hole model, which incorporates the concept of site availability in order to model decreasing mobility in the mixture, as the ionic liquid concentration increases. We compare with aqueous ionic liquid mixtures, as water is a solvent which best fulfills the approximations inherent in our theory. The conductivity expression is couched in terms of a single-fitting parameter and is able to reproduce a range of conductivity data with good accuracy.

Communications: The fractional Stokes-Einstein equation: application to water.

Previously [K. R. Harris, J. Chem. Phys. 131, 054503 (2009)] it was shown that both real and model liquids fit the fractional form of the Stokes-Einstein relation [fractional Stokes-Einstein (FSE)] over extended ranges of temperature and density. For example, the self-diffusion coefficient and viscosity of the Lennard-Jones fluid fit the relation (D/T) = (1/eta)(t) with t = (0.921+/-0.003) and a range of molecular and ionic liquids for which high pressure data are available behave similarly, with t values between 0.79 and 1. At atmospheric pressure, normal and heavy water were also found to fit FSE from 238 to 363 K and from 242 to 328 K, respectively, but with distinct transitions in the supercooled region at about 258 and 265 K, respectively, from t = 0.94 (high temperature) to 0.67 (low temperature). Here the recent self-diffusion data of Yoshida et al. [J. Chem. Phys. 129, 214501 (2008)] for the saturation line are used to extend the high temperature fit to FSE to 623 K for both isotopomers. The FSE transition temperature in bulk water can be contrasted with much lower values reported in the literature for confined water.

The fractional Stokes-Einstein equation: application to Lennard-Jones, molecular, and ionic liquids.

The fractional Stokes-Einstein (FSE) relation, (D/T) proportional to eta(-t), is shown to well correlate the molecular dynamics results of Meier et al. [J. Chem. Phys. 121, 3671 (2004); ibid. 121, 9526 (2004)] for the viscosity (eta) and self-diffusion coefficient (D) of the Lennard-Jones fluid in the liquid and dense supercritical states, with the exponent t = (0.921+/-0.003). The Stokes-Einstein number n is viscosity dependent: ln n = const + (t - 1)ln eta. Molecular and ionic liquids for which high-pressure transport property data are available in the literature are shown to exhibit the same behavior with 0.79 < t < 1. Water is also shown to fit the FSE at atmospheric pressure, with a change in exponent t from 0.94 to 0.67 at about 258 K (265 K for D(2)O), but the FSE holds only approximately at high pressures. It sometimes argued that FSE in supercooled liquids near the glass transition is a diagnostic for dynamic heterogeneity, but this work shows that the FSE holds in normal liquids far from the glass transition. This result may provide a reference for complex liquids such as viscous glass formers that show a transition (dynamic crossover) in the temperature dependence of the viscosity and network-bonded liquids such as water.

On the Use of the Angell-Walden Equation To Determine the "Ionicity" of Molten Salts and Ionic Liquids.

In this work, the Angell analysis of Walden plots of the conductivity of ionic liquids and other electrolytes against viscosity is used to examine simple molten salts at high temperatures, a test that does not appear to have been made previously. It is found that many simple salts such as alkali metal fluorides and chlorides are predicted to be "superionic" as their Walden plots fall above the arbitrary reference line introduced by Angell, which passes through the datum point for 1 M aqueous KCl at 25 °C. This contradicts long-standing molecular dynamics evidence in the literature showing that these salts conduct simply by ion migration in an electric field. Zinc chloride is also predicted to be "ideal", whereas one would expect it to be "subionic" in Angell's terminology given that it is an associated salt. Results for certain protic ionic liquids are also contradictory. Therefore, Angell-Walden analyses of this type do not convey any useful information other than a qualitative ranking of the conductivity of similar ionic liquids at a given viscosity and their use for estimating "ionicity" is best discontinued. It cannot and should not be used for classifying the interactions in ionic liquids. Instead, it is argued that an examination of Laity resistance coefficients is more useful in any discussion of true association in molten salts and ionic liquids where known examples show negative like-ion resistance coefficients with NE deviation parameters close to unity. Such an approach could be more fruitful in understanding the transport properties of molten salts and ionic liquids rather than simple comparisons of viscosity and conductivity.