High-frequency ultrasonic speckle velocimetry in sheared complex fluids
Abstract
High-frequency ultrasonic pulses at 36 MHz are used to measure velocity profiles in a complex fluid sheared in the Couette geometry. Our technique is based on time-domain cross-correlation of ultrasonic speckle signals backscattered by the moving medium. Post-processing of acoustic data allows us to record a velocity profile in 0.02--2 s with a spatial resolution of 40 m over 1 mm. After a careful calibration using a Newtonian suspension, the technique is applied to a sheared lyotropic lamellar phase seeded with polystyrene spheres of diameter 3--10 m. Time-averaged velocity profiles reveal the existence of inhomogeneous flows, with both wall slip and shear bands, in the vicinity of a shear-induced ``layering'' transition. Slow transient regimes and/or temporal fluctuations can also be resolved and exhibit complex spatio-temporal flow behaviors with sometimes more than two shear bands.
Cite
@article{arxiv.cond-mat/0311072,
title = {High-frequency ultrasonic speckle velocimetry in sheared complex fluids},
author = {S. Manneville and L. Becu and A. Colin},
journal= {arXiv preprint arXiv:cond-mat/0311072},
year = {2009}
}
Comments
15 pages, 18 figures, submitted to Eur. Phys. J. AP