Ultrasonic method to characterize shear wave propagation in micellar fluids.

Viscoelastic micellar fluid characteristics have been measured with mechanically generated shear waves and showed good agreement to shear oscillatory methods. In this paper, shear waves in wormlike micellar fluids using ultrasound were successfully generated and detected. Micellar fluids of different concentrations (100, 200, 300, and 400 mM) were studied with ultrasound-based and conventional rheology methods. The measured micellar fluid complex modulus from oscillatory shear tests between 0.001 and 15.91 Hz was characterized with an extended Maxwell fluid model. The elastic and viscous parameters found using rheological testing were used to estimate shear wave phase velocity over a frequency range from 100 to 500 Hz, and compared to shear wave velocity measured with ultrasound-based methods with a mean absolute error 0.02 m/s. The shear wave frequency content was studied and an increase in shear wave center frequency was found as a function of micellar fluid concentration. Moreover, the bias found in the shear wave group velocity with respect to rheological measurement is attributed to the micellar fluid viscous component. Finally, the shear wave phase velocity evaluated at the center frequency agreed well with the rheological measurements.