Settling dynamics of Brownian elastic filaments in centrifuge systems*

The settling dynamics of filaments in viscous fluids is a fundamental problem in fluid mechanics with important implications in different fields of industry and science. For instance, the ultracentrifuge technique has been widely used to separate DNA filaments based on their length. In the present study, we investigate the dynamics of a single Brownian elastic filament in centrifuge systems. For the numerical scheme, we discretized the filament in the bead-spring fashion. We implement the Brownian Dynamics method accounting for hydrodynamic interactions to evolve the beads' positions in time and capture the dynamics of the filament. We show that as one increases the centrifuge rotational velocity, the filament's configuration tends to collapse into dense structures leading to higher sedimentation factors. For strong centrifuge forces, the filament tends to acquire a stable configuration composed of a condensed head with a trailing stretched tail. The intense drag at the tail induces the reduction of sedimentation. We find that the stability of such a configuration is due to the field-induced knot-tightening mechanism caused by the tension introduced by the drag difference between the tail and head structures. Also, we find hydrodynamically induced super-diffusive-like dynamics of the filament in the plane perpendicular to the settling direction.