Direct visualization of shear waves in viscoelastic fluid using microspheres

Wormlike micellar fluids, being viscoelastic, support shear waves. Shear waves in 500 mM CTAB-NaSal micellar fluid were visualized by seeding the fluid with 212-250 μm diameter polyethylene microspheres. This method was compared to visualization through birefringence induced by shear stress in the fluid. Measured shear wave speeds were 733 and 722 mm/s, respectively, for each technique. Particle displacement was a sinusoidal function of time and displacement amplitude decreased quadratically with distance from the source. This supports the possibility of using particle amplitude measurements as a measure of attenuation even at low fluid concentration where birefringence visualization techniques fail.