Simultaneous concentration and velocity maps in particle suspensions under shear from rheo-ultrasonic imaging

We extend a previously developed ultrafast ultrasonic technique [Gallot et al., Rev. Sci. Instrum. 84, 045107 (2013)] to concentration field measurements in non-Brownian particle suspensions under shear. The technique provides access to time-resolved concentration maps within the gap of a Taylor-Couette cell simultaneously to local velocity measurements and standard rheological characterization. Benchmark experiments in homogeneous particle suspensions are used to calibrate the system. We then image heterogeneous concentration fields that result from centrifugation effects, from the classical Taylor-Couette instability and from sedimentation or shear-induced resuspension.