Density−Viscosity Product of Small-Volume Ionic Liquid Samples Using Quartz Crystal Impedance Analysis

McHale, Glen, Hardacre, Christopher, Ge, Rile, Doy, Nicola, Allen, Ray, MacInnes, Jordan, Bown, Mark and Newton, Michael (2008) Density−Viscosity Product of Small-Volume Ionic Liquid Samples Using Quartz Crystal Impedance Analysis. Analytical Chemistry, 80 (15). pp. 5806-5811. ISSN 0003-2700

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Abstract

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, ρη. 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 ([C4mim][OTf]), were measured. 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. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. 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. 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 10%. 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 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 √(ρη) ≈ 18 kg m−2 s−1/2, but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Item Type:	Article
Subjects:	F100 Chemistry
Department:	Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User:	Ay Okpokam
Date Deposited:	01 Feb 2012 10:43
Last Modified:	12 Oct 2019 19:06
URI:	http://nrl.northumbria.ac.uk/id/eprint/5153

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