Acoustically Trapping Nanoparticles

Micrometer-sized particles can be trapped in place against a flow using acoustic waves. But smaller nano-sized particles feel less radiation pressure from acoustic waves, and so keep moving in the flow. But new work shows that it is possible to trap those nanoparticles with some additional help.

In this case, researchers seeded their flow with microparticles that were held in place by acoustic waves against the background flow. When nanoparticles were added to the mix, they remained trapped in the wells between microparticles due to a combination of acoustic forcing and the hydrodynamic shielding of the nearby large particles. (Image credit: P. Czerwinski; research credit: A. Pavlič and T. Baasch; via APS)

#acousticTrapping #acoustics #fluidDynamics #microfluidics #particleSuspension #physics #science

Bigger Particles Slide Farther

Mudslides and avalanches typically carry debris of many shapes and sizes. To understand how debris size affects flows like these, researchers use simplified, laboratory-scale experiments like this one. Here, researchers mix a slurry of silicone oil and glass particles of roughly two sizes. The red particles are larger; the blue ones smaller. Sitting in a cup, the mixture tends to separate, with red particles sinking faster to form the bottom layer and smaller blue particles collecting on top. And what happens when such a mixture flows down an incline? The smaller blue particles tend to settle out sooner, leaving the larger red particles in suspension as they flow downstream. (Video and image credit: S. Burnett et al.)

#2024gofm #flowVisualization #fluidDynamics #gravityCurrent #particleSuspension #physics #science #suspension #viscousFlow

Quick-Drying, Fast-Cracking

Water droplets filled with nanoparticles leave behind deposits as they evaporate. Like a coffee ring, particles in the evaporating droplet tend to gather at the drop’s edge (left). As the water evaporates, the deposit grows inward (center) and cracks start to form radially. After just a couple minutes, the solid deposit covers the entire area of the original droplet and is shot through with cracks (right).

Researchers found that the cracks’ patterns and propagation are predictable through a model that balances the local elastic energy and and the energy cost of fracture. They also found that the spacing between radial cracks depends on the deposit’s local thickness. Besides explaining the patterns seen here, these cracking models could help analyze old paintings, where cracks could hide information about the artist’s methods and the artwork’s condition. (Image and research credit: P. Lilit et al.; via Physics Today)

#art #cracking #deposition #droplets #drying #evaporation #fluidDynamics #particleSuspension #physics #science

“There is a crack in everything…”

When millimeter-sized drops of water infused with nanoparticles dry, they leave behind complex and beautiful residues. As water continues evaporating, the residues warp, bend, and crack. In this video, researchers set their science to the music of Leonard Cohen. The results resemble blooming flowers and flying water fowl. If you’d like to learn more about the science behind the art, check out the two open-access papers linked below. (Video and image credit: P. Lilin and I. Bischofberger; submitted by Irmgard B.; see also P. Lilin and I. Bischofberger and P. Lilin et al.)

#coffeeRings #cracking #droplets #drying #evaporation #fluidDynamics #fluidsAsArt #granularMaterial #particleSuspension #physics #science