# Applied Math Seminar (AMS)

#### Interactions of Passive and Active Capillary Disks

Speaker: Daniel Harris, Brown University (host: Ristroph)

Location: TBA

Date: Friday, March 26, 2021, 2:05 p.m.

Synopsis:

In this talk, I will introduce capillary disks - hydrophobic disks at the capillary scale whose weight is supported on the fluid interface by virtue of hydrostatics and capillarity.

I will begin by presenting direct measurements of the attractive force between two  capillary disks.  It is well known that objects at a fluid interface may interact due to the mutual deformation they induce on the free surface, however few direct measurements of such forces have been reported. In the present work, we characterize how the attraction force depends on the disk radius, mass, and relative spacing, and rationalize our findings with a scaling analysis.

When such disks are then deposited on a vibrating fluid bath, the relative vertical motion of the disk and the interface leads to the generation of outwardly propagating capillary waves. We demonstrate that when the rotational symmetry of an individual particle is broken, the particles can steadily self-propel along the interface and interact with each other via their collective wavefield, forming a myriad of cooperative dynamic states. Our discovery opens the door to further investigations of this active system with fluid-mediated interactions at intermediate Reynolds numbers.

Ongoing work and future directions will be discussed.