Harris Lab entry wins American Physical Society’s Gallery of Soft Matter scientific visualization competition

The March Meeting of the American Physical Society was held March 5-10 in Las Vegas, where a Brown Engineering video entry into the Gallery of Soft Matter was awarded top honors. The Gallery of Soft Matter Physics is in its second year, and is a poster and video competition from the APS March Meeting that showcases the elegance and aesthetics of soft matter to highlight the work of the soft matter community to fellow researchers and the general public.

Submissions were judged on both striking visual qualities and scientific interest. The gallery contest was first established last year, inspired in part by the society’s hugely successful annual Gallery of Fluid Motion. There were five winners in total, three video entries and two posters, and all five will have the chance to present their work at next year’s March meeting in Minneapolis, Minnesota.

Alireza ("Navid") Hooshanginejad is a Hibbitt postdoctoral fellow in Professor Dan Harris’ laboratory who led the overall project, with help from fellow postdoc Robert Hunt, Ph.D. student Jack-William Barotta, researcher Giuseppe Pucci of the National Research Council of Italy (CNR), Wheeler School’s Victoria Spradlin, and Harris. Barotta also composed the music behind the video. 

Hooshanginejad and his lab mates built on the work by former undergraduate Ian Ho ’21 (now a graduate student at Stanford) who performed some of the first direct measurements of the so-called “Cheerios effect.” The weight of small objects like cereal, grains of pollen, or small coins floating in liquid are insufficient to break the surface tension, but enough to put a tiny dent in the surface. If sufficiently close, items will naturally drift toward each other. 

This group applied a  scaling law from those experiments relating the strength of the capillary attraction in the Cheerios effect to the mass, diameter, and spacing of the disks. By embedding each disk with a small magnet, they found that at a certain spacing between the disks the two opposing forces balance, and the disks settle into a standoff. They also noted that certain patterns formed under different conditions. For instance, repulsion is the dominant force when the density of particles is low, so the particles form a crystal lattice. Increase the density, and the attractive force gains sway because the particles are closer together. That’s when the particles form clusters. Increase the attractive force even more, and the clusters merge to form stripes.  Similar patterns have been previously observed in microscopic systems that are also governed by a competition between attractive and repulsive forces.