1. In Active Fluids
Generalised hydrodynamic theory can be employed to describe dynamics of active fluids that consist microscopically of elongated, self-propelled particles. Such `active polar fluids’ are intrinsically out of equilibrium and show rich, self-organized dynamics; for example in flocks of birds that form complex shapes. We are interested in a subset of these systems which exhibit elasticity as well as activity, such as systems consisting of connected self-propelled (active) colloids that model the motion of organelle filaments in motility assays.
Motivated by experimental actin assays, we study the emergent dynamics of this animated filament constrained to move in a plane. Geometric constraints along with the polarity of the colloids results in an active compressive force that tends to buckle the lament. We find that depending on the type of constraint at the fixed end (clamped,pivoted or torsional spring), oscillatory or divergent instability occurs for an initially straight filament. A flutter boundary is observed in the case of a torsionally clamped lament below which oscillatory instabilities are supported. Above the flutter limit, the filament displays divergent instability similar to a pivoted end. This work sets the stage for a more detailed exploration of the complex interplay between intrinsic activity, elasticity and response to extrinsic fields in low-Reynolds number swimmers.
13. Instabilities and Spatiotemporal Dynamics of Active Elastic Filaments, Journal of the Royal Society Interface, 17, 20190794, 2020.