Acoustic energy harnessed to soften shear-thickening fluids | 9/14/2016 | Staff
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Researchers are using ultrasonic waves to manipulate the viscosity of shear-thickening materials, turning solids to slush—and back again.

The study, "Using Acoustic Perturbations to Dynamically Tune Shear Thickening in Colloidal Suspensions," was published Sept. 17 in Physical Review Letters.

Fluids - Class - Materials - Liquid - Solidify

Shear-thickening fluids are a class of materials that flow like liquid but solidify when squeezed or sheared quickly, such as quicksand and Oobleck, the children's play slime. Technical applications for the material range from soft body armor and astronaut suits to 3-D printing metals and ceramics.

But the shear-thickening process can be uncooperative: The more you manipulate the material, the more it solidifies, which in the case of 3-D printing and the manufacture of concrete can lead to gunked-up nozzles and jammed hoppers.

Itai - Cohen - Professor - Paper - Author

Itai Cohen, professor of and the paper's co-senior author, previously found a way to manipulate—or "tune"—the material by breaking apart the rigid structures or force chains formed by the particles in these suspensions through perpendicular oscillation. But that method proved to be impractical. It isn't easy, after all, to shake and twist a factory pipe.

Cohen and Ph.D. student Meera Ramaswamy partnered with Brian Kirby, professor of engineering, and Ph.D. student Prateek Sehgal, who have been using acoustic transducers to manipulate micro- and nanoscale particles in Kirby's lab.

Sehgal - Device - Plate - Piezo—that - Waves

Sehgal developed a simple but effective device that consists of a bottom plate with an acoustic transducer—called a piezo—that generates ultrasonic waves.

"When you excite that piezo at a...
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