Brown School of Engineering Ph.D. student Jack-William Barotta received the Emerging Soft Matter Excellence (ESME) award, conferred by the American Physical Society Division of Soft Matter (DSOFT) at the 2026 American Physical Society Global Physics Summit, held in Denver.
Barotta is a fifth-year Ph.D. candidate who works in Associate Professor Dan Harris’ lab and studies self-propulsion and collective motion of objects at a vibrating fluid interface. In the last few years, wave-propelled particles at an air-fluid interface have been shown to exhibit a host of both static and dynamic collective states, with even the two-body problem admitting multiple modes of interaction. The interaction between such particles is governed by a combination of a static capillary attractive force, colloquially known as the “Cheerios Effect” and a dynamic wave-mediated force that oscillates from attractive to repulsive over a length scale set by the wavelength.
Barotta’s work, “Wave-mediated capillary assembly on a fluid interface,” demonstrates the simple problem of the dynamics of interacting “point sources” (small superhydrophobic spheres) that sit atop a vibrating fluid interface. The spheres admit multiple stable equilibria, quantized by the wavelength, with the existence and stability of the equilibria being a function of driving and fluid parameters. A previously established quasi-potential model, which provides predictions for both the wavefield and the resulting wave-mediated force law, is compared with experimental results, allowing for direct verification of the stable equilibrium spacing as a function of system parameters. With an understanding of the pairwise interaction, stable assemblies of objects are formed, with lattice constants and structure capable of being dynamically manipulated by the driving parameters of the forcing itself.