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New measurements of the viscosity of 1-butyl-3-methylimidazolium triflate ([BMIM][OTf]) and 1-hexyl-3-methyl-imidazolium triflate ([HMIM][OTf]) have been carried out at high pressures, using a vibrating-wire technique operated in the forced mode of oscillation. The measurements for [BMIM][OTf] have been performed along six isotherms from 298 to 358 K at pressures up to 50 MPa. The viscosity measurements for [HMIM][OTf] have been carried out along five isotherms from 303 to 358 K at pressures up to 50 MPa. The estimated uncertainty of the measurements is less than U(η) = 0.02•η for viscosities up to 68 mPa•s and less than U(η) = 0.026•η for higher viscosities, with a confidence level of 0.95 (k = 2). For both ionic liquids, complementary density measurements have been performed using an Anton Paar HP densimeter in the same temperature and pressure ranges as those used for the viscosity measurements. The density results have an uncertainty smaller than U(ρ) = 0.002•ρ with a confidence level of 0.95 (k = 2). The viscosity results were correlated with the density data using a previously described hard-sphere-based technique. The individual correlations are able to describe the viscosity results for each liquid with an uncertainty smaller than the estimated uncertainty of the experimental data. The effect of alkyl substituents on the viscosity and the density of these ionic liquids has been analyzed. For this purpose, previously published results for the viscosity and density of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) have been considered in addition to the data obtained in the present work for [BMIM][OTf] and [HMIM][OTf].

New measurements for the viscosity and density of poly(ethyleneglycol) 200 [PEG 200] and of poly(ethyleneglycol) 600 [PEG 600], at pressures up to 50 MPa, are presented. The temperature range of the measurements performed for PEG 200 was from 293 to 348 K and for PEG 600 was from 303 to 348 K. A vibrating wire viscometer operated in the steady-state mode was used to carry out the measurements with an estimated overall uncertainty less than U(η) = 0.02·η, for viscosities up to 68 mPa s, and less than U(η) = 0.026·η, for higher viscosities with a confidence level of 0.95 (k = 2). Complementary density measurements for both PEGs were performed in the same ranges of temperature and pressure as for the viscosity measurements, using an Anton Paar HP vibrating tube densimeter, with an estimated overall uncertainty of about U(ρ) = 0.002·ρ with a confidence level of 0.95 (k = 2). Moreover, pressure–viscosity coefficients were obtained for both PEGs. A method based on a dense hard-sphere fluid theory was used to correlate the viscosity data with the density, for both PEGs, with a deviation of the experimental results less than 1%. A modified Tait equation was used to correlate the density results with temperature and pressure.

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