Hydrodynamic shock and instability in sedimenting colloidal suspensions along a surface

We combine experiments, large-scale simulations, and a continuum model to study the emergence of a coherent density profile in a suspension of passive particles sedimenting near an inclined plane. Sedimenting colloids form a shock when there are sharp density gradients in the suspension and agree well with a solution to a modified Burger's equation. We also observe the formation of an instability at the front of the shock that is different from the case of driven microrollers¹ and other fluid-like instabilities in that the amplitude does not grow exponentially. The instability is characterized by a wavelength controlled by the gravitational height, the typical height of the particles above the inclined plane.

1. Driscoll, Michelle, et al. "Unstable fronts and motile structures formed by microrollers." Nature Physics 13.4 (2017): 375.