A. Hooshanginejad et al., 2023
Scientific research often produces striking visuals. This year’s Soft Matter Physics Gallery winners are no exception. The award-winning video entry, selected at his March meeting of the American Physical Society in Las Vegas, Nevada last week, utilizes the Cheerios effect, the physics of clogs, and the physics behind tears of wine to create bubbles. It was characterized by longevity. Submissions were judged on both impressive visual quality and scientific interest. The gallery contest was first established last year, inspired by the association’s highly successful annual Gallery of Fluid Motion. All five of this year’s winners will have the opportunity to present their work at a conference in Minneapolis, Minnesota next March.
mermaid cereal
Mermaid Cereal: Exploring the ‘Cheerios Effect’.
As we previously reported, the “Cheerios effect” describes the physics behind why the last few delicious little “O’s” in cereal tend to clump together in a bowl. This effect can also be seen in pollen (or mosquito egg) grains floating on a pond, or small coins floating in a bowl of water. The culprit is a combination of buoyancy, surface tension and the so-called “meniscus effect”. It all comes down to a kind of capillary action. Essentially, the Cheerios mass is insufficient to break the surface tension of the milk. However, if the two Cheerios are close enough, it is enough to make small indentations on the surface of the milk in the bowl so that they naturally drift towards each other. The “dents” are united, and the “O” is united. Add another Cheerio of his to the mix and it too will drift towards its fellow ‘O’, following the curvature of the milk.
It’s roughly on the scale of a mosquito’s weight, so it’s difficult to measure the actual forces acting on such a small scale. Typically, this is done by placing sensors on the object, using the sensors to deflect its natural movement, and placing it floating in a container. But Cheerios is so small that this was not a viable approach. Her Alireza Hooshanginejad, a postdoc at Brown University, and cohorts used her two 3D-printed plastic discs, about the size of her Cheerio, and placed a small magnet in one of them. . The disks are then floated in a small aquarium surrounded by electric coils and drifted together (attraction). The coil then generates a magnetic field that pulls the magnetized disc away from its non-magnetized partner (repulsion).
hoshan guinea jard and others. were able to derive a scaling law from experiments relating the strength of capillary action in the Cheerios effect to the mass, diameter and spacing of the discs. For example, we found that at a certain spacing between the discs, the two opposing forces balance and the disc settles on the standoff. They also noted that specific patterns form under different conditions. For example, when the particle density is low, the repulsive force becomes the dominant force, so the particles form a crystal lattice. Increasing the density swings the attraction as the particles move closer together. That’s when particles form clusters. Further increasing the suction force causes the particles to become streaky.
