Motion transition of active filaments: rotation without hydrodynamic interactions

We investigate the dynamics of an active semiflexible filament in a bead–rod model involving dynamically the hydrodynamic interaction (HI), active force, filament flexibility and viscous drag. We find that the filament can show three distinct types of motion, namely, translation, snaking and rotation, with the variation of the rigidity or active force. The transition from translation to snaking is continuous and mainly due to transverse instability, while the snaking–rotation transition is first-order like and shown to result from a type of symmetry breaking associated with the shape kinematics. Of particular interest, we find that HI is not necessary for the rotation or snaking motion, but can enlarge remarkably the parameter regions in which they can occur. Combining with local collisions, we show that, for the parameter region where HI is essential for the maintenance of rotation curvature of a single filament, HI is also essential for the emergence of collective vortexes. Thus, our findings provide new insights into the subtle role of HI in the formation of collective structures in active systems