The density, refractive index, interfacial tension, and viscosity of ionic liquids (ILs) [EMIM][EtSO 4] (1-ethyl-3-methylimidazolium ethylsulfate), [EMIM][NTf 2] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), [EMIM][N(CN) 2] (1-ethyl-3-methylimidazolium dicyanimide), and [OMA][NTf 2] (trioctylmethylammonium bis(trifluoromethylsulfonyl)imide) were studied in dependence on temperature at atmospheric pressure both by conventional techniques and by surface light scattering (SLS). A vibrating tube densimeter was used for the measurement of density at temperatures from (273.15 to 363.15) K and the results have an expanded uncertainty ( k = 2) of +/-0.02%. Using an Abbe refractometer, the refractive index was measured for temperatures between (283.15 and 313.15) K with an expanded uncertainty ( k = 2) of about +/-0.0005. The interfacial tension was obtained from the pendant drop technique at a temperature of 293.15 K with an expanded uncertainty ( k = 2) of +/-1%. For higher and lower temperatures, the interfacial tension was estimated by an adequate prediction scheme based on the datum at 293.15 K and the temperature dependence of density. For the ILs studied within this work, at a first order approximation, the quantity directly accessible by the SLS technique was the ratio of surface tension to dynamic viscosity. By combining the experimental results of the SLS technique with density and interfacial tension from conventional techniques, the dynamic viscosity could be obtained for temperatures between (273.15 and 333.15) K with an estimated expanded uncertainty ( k = 2) of less than +/-3%. The measured density, refractive index, and viscosity are represented by interpolating expressions with differences between the experimental and calculated values that are comparable with but always smaller than the expanded uncertainties ( k = 2). Besides a comparison with the literature, the influence of structural variations on the thermophysical properties of the ILs is discussed in detail. The viscosities mostly agree with values reported in the literature within the combined estimated expanded uncertainties ( k = 2) of the measurements while our density and interfacial tension data differ by more than +/-1% and +/-5%.

Within this work, viscosity and interfacial tension of selected ionic liquid cosolvent mixtures, [EMIM][EtOSO3] (1-ethyl-3-methyl-immidazolium ethyl sulfate) with water and ethanol, were studied as a function of composition by surface light scattering (SLS) and the pendant drop method in a consistent manner, allowing a close insight into the nature of interactions. Here, we show that the viscosity behavior clearly reflects the bulk structure of the ionic liquid cosolvent mixtures and correlates to the fluid structure at the phase boundary. In contrast to former work, we found the viscosity of ionic liquid [EMIM][EtOSO3] to be decreasing the stronger by small amounts of the cosolvents and the lower their dielectric constant. Furthermore, two distinct trends for the dependence of the viscosity on the cosolvent concentration were resolved. These were assigned to ion-dipole interactions dominating in the salt-rich region and to dipole-dipole interactions in the diluted one. A crossover between both regions is reflected by the interfacial tension data, where it seems that up to a "critical" concentration almost no cosolvent is present at the phase boundary.

This work presents a comprehensive experimental study of various thermophysical properties of an azeotropic refrigerant mixture of 65 mass% R365mfc (1,1,1,3,3-pentafluorobutane) and 35 mass% Galden HT 55 (perfluoropolyether). Light scattering from bulk fluids has been applied for measuring both the thermal diffusivity and the speed of sound in the liquid and vapor phases under saturation conditions, between 293 K and the liquid-vapor critical point at 450.7 K. Furthermore, the speed of sound has been measured for the superheated-vapor phase along nine isotherms, between 393 and 523 K and up to a maximum pressure of about 2.5 MPa. For temperatures between 253 and 413 K, light scattering by surface waves on a horizontal liquid-vapor interface has been used for simultaneous determination of the surface tension and kinematic viscosity of the liquid phase. With light scattering techniques, uncertainties of less than ±2.0%, ±0.5%, ±1.5%, and ±1.5% have been achieved for the thermal diffusivity, sound speed, kinematic viscosity, and surface tension, respectively. In addition to vapor-pressure measurements between 304 and 448 K, the density was measured between 273 and 443 K using a vibrating-tube method. Here, measurements have been performed in the compressed-and saturated-liquid phases with uncertainties of ±0.3% and ±0.1%, respectively, as well as for the superheated vapor up to a maximum pressure of about 3 MPa with an uncertainty between ±0.3% and ±3%. Critical-point parameters were derived by combining the data obtained by different techniques. 449 0195-928X/07/0400-0449/0 © 2007 Springer Science+Business Media, LLC 450 Fröba, Kremer, Leipertz, Flohr, and Meurer

No abstract

Dynamic light scattering (DLS) has been used for the measurement of several thermophysical properties of a quaternary refrigerant mixture R-125/143a/32/134a in its liquid phase under saturation conditions. The thermal diffusivity and sound speed have been obtained by light scattering from bulk fluids over a temperature range from about 293 K up to the liquid-vapor critical point. By applying the method of DLS to a liquid-vapor interface, also called surface light scattering (SLS), the saturated liquid kinematic viscosity and surface tension can be determined simultaneously. These properties have been measured from about 243 to 343 K. The results are discussed in comparison with literature data and with a simple prediction method based on the mass-weighted properties of the pure components, expressed as functions of the reduced temperature. Once again, the simple prediction method was shown to be applicable for the calculation of different transport and other thermophysical properties of multicomponent refrigerant mixtures and this with sufficiently high accuracy for technical practice. Moreover, the input data for the simple prediction scheme can be reduced without loss of accuracy by treating binary or ternary mixtures as a subset of the multicomponent mixture.