Abstract
We describe how high-frequency ultrasound can be used to measure and follow velocity profiles in complex fluids sheared in the Couette geometry with a 0.5–1 mm gap. The technique provides a spatial resolution of 40 μ m and velocity profiles can be recorded every second typically. Such ultrasonic velocimetry is coupled to a standard rheometer. The resulting “ultrasonic rheo-velocimeter” is tested on various complex fluids that display both inhomogeneous velocity profiles and temporal fluctuations close to a shear-induced transition: a lamellar phase, a triblock copolymer, a concentrated emulsion, and an organogel.
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