Mind the gap: a new kind of fingering instability in colloidal rollers by Michelle Driscoll
Host: Prof. Lisa Manning/ Contact: Yudaisy Salomón Sargentón, 315-443-5960
202 Physics Bldg.
Refreshments at 3:30 and the talk starting at 3:45pm
When colloidal particles are rotated adjacent to nearby floor, strong advective flows are generated around them, even quite far away. When a group of these microrollers is driven, the strong hydrodynamic coupling between particles leads to formation of new, emergent structures: an initially uniform front of microrollers evolves first into a shock, which then quickly becomes unstable, emitting fingers of a well-defined wavelength. Our experiments and simulations confirm that this instability is very different than typical fingering instabilities, where size scale selection is a consequence of competing stresses. In this case, the instability arises only due to hydrodynamic interactions, and it is controlled by a single geometric parameter: the particle-floor gap. We have developed a simplified continuum model that reproduces the instability behavior. This model confirms that instability we observe in the experiments is indeed a direct consequence of the inward flows created by the interactions between the particles and the nearby solid surface.