title: Viscoelastic properties of room temperature ionic liquids.
abstract: The sound absorption coefficient alpha and sound velocity nu(S) have been measured for 1-alkyl-3-methylimidazolium hexafluorophosphate [Cn mim]PF(6), with n = 8,6,4 and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4 mim]TFSI, at the frequencies of 11.3, 34.9, and 57.7 MHz in the temperature range from 293 to 393 K. From the obtained alpha and available viscosity data, [Cn mim]PF(6) with large n proves to be no longer Newtonian liquids at room temperatures. Applying a Maxwell viscoelastic model with the elastic modulus G of a spring and the shear coefficient gamma of a dashpot to the experimental frequency dependence of alpha, one finds that G is insensitive to n, while the relaxation time tau(= gamma/G), which is on the order of nanoseconds, does depend on n.
authors.affiliation: Department of Physics, Kyoto University, 606-8502 Kyoto, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Makino
authors.forename: Ryoko
authors.initials: R
authors.lastname: Kishikawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Mizoshiri
authors.forename: Shinichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Makoto
authors.initials: M
authors.lastname: Yao