Measurement of Dynamic Shear Impedance of Low Viscosity Liquids at Ultrasonic Frequencies

Abstract

An instrument is described for measuring shear mechanical properties of liquids with viscosities as low as 0.5 cP. Operation is based on an ultrasonic‐shear‐reflectance method previously used only for more viscous materials [W. P. Mason et al., Phys. Rev. 75, 936–946 (1949)]. In the present apparatus, the considerable increase in sensitivity has resulted primarily from use of an improved method of determining small changes in phase shift for ultrasonic waves reflecting from the solidliquidinterface of the instrument. Results at 40 Mc/sec for complex shear impedance and dynamic viscosity are presented for a number of pure liquids. Application to studies of polymer solutions is illustrated by data for a series of polystyrene di‐n‐butyl phthalate solutions. An ultrasonic method for crosschecking results is described in Appendix A.