Ultrafast ultrasonic imaging coupled to rheometry: Principle and illustration

Abstract

We describe a technique coupling standard rheology and ultrasonic imaging with promising applications to characterization of soft materials under shear. Plane wave imaging using an ultrafast scanner allows to follow the local dynamics of fluids sheared between two concentric cylinders with frame rates as high as 10 000 images per second, while simultaneously monitoring the shear rate, shear stress, and viscosity as a function of time. The capacities of this "rheo-ultrasound" instrument are illustrated on two examples: (i) the classical case of the Taylor-Couette instability in a simple viscous fluid and (ii) the unstable shear-banded flow of a non-Newtonian wormlike micellar solution.

Simultaneous Concentration and Velocity Maps in Particle Suspensions under Shear from Rheo-Ultrasonic Imaging

“…The experimental setup used in the present study has already been described at length in Gallot et al [13] and…”

“…These difficulties probably explain why applications of ultrasonic imaging to study the local particle concentration in suspensions have remained very scarce until recent years [41][42][43]. In the following, we shall build upon a previous rheo-ultrasonic setup designed for local velocimetry of complex fluid flows within a concentric cylinder (Taylor-Couette, TC) geometry [13] to perform local volume fraction measurements. Multiple scattering is minimized by using a small-gap TC cell.…”

“…UIV and its derivatives have proved successful not only for blood flow measurements [28,29] but also for applications to hydrodynamics [30], to rheology [13,31] or to industrial situations involving optically opaque suspensions [32,33]. These velocimetry techniques rely upon the measurement of local displacements through cross-correlation of successive speckle signals received after successive pulses are sent through the scattering material.…”

“…[13], that allows one to go from the raw ultrasonic speckle signal p(r, z) to the beam-formed image pBF(r, z).…”

“…We extend a recently developed rheo-ultrasonic setup [13] to access the concentration field in non-Brownian suspensions subject to both homogeneous and heterogeneous flows. In Section II, we briefly review previous work on acoustic characterization of suspensions and recall the technical specifications of our ultrasonic scanner.…”