Viscoelastic properties of low-viscosity liquids studied with thickness-shear mode resonators

The network analysis method was applied to AT cut quartz blanks (f(0) = 10 MHz), which were loaded with liquids of low and medium viscosity (water, methanol, ethanol, l-propanol, l-butanol, glycerol solutions). The shift of the resonance frequency Delta f could be separated into a term due to rigidly coupled mass Delta f(rig) and a term due to viscous damping Delta f - Delta f(rig). From the difference Delta f - Delta f(rig) and the broadening of the resonance curve, the complex shear modulus G = G' + i omega eta(L) was calculated. The viscosity coefficients eta(L) are in good agreement with literature data. As G' + 0, it can be concluded that the examined fluids also reveal elasticity at shear frequencies in the MHz range. For the low-viscosity liquids, elastic contributions resulting from collective interactions of molecules are measurable but small and neglectable in most applications. The medium viscous liquid glycerol (98%) begins to exhibit considerable elasticity, resulting from the relaxation of separate molecules.