The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of square root(rho eta) approximately 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained these 12 all had a Newtonian response. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods the pure ionic liquids had the largest difference of approximately 10%. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, with concentration varied using methanol, was tested and also found to provide a Newtonian response. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimiclazolium trifluoromethylsulfonate (), were measured. Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. McHale, Glen Hardacre, Chris Ge, Rile Doy, Nicola Allen, Ray W K MacInnes, Jordan M Bown, Mark R Newton, Michael I Density-viscosity product of small-volume ionic liquid samples using quartz crystal impedance analysis.
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