Evolution of a sedimenting colloidal sheet

A sedimenting 2D colloidal sheet shows curious stability and nonlinear behavior at small Re around 10^-3, which should be in the linear Stokes regime. Small-scale mechanical instabilities develop in the form of dynamic swirling of particles in transient clusters, which generate multiple critical points and highly entangled vortex lines. This nonlinearity results from the topological nature of the fluid flow. Spatial organization of swirling motions determines the overall shape. The observed phenomena may challenge our notion of a low Reynolds number hydrodynamic problem, and holds value for understanding other dissipative dynamical systems.