Flagellated microswimmers: hydrodynamics in thin liquid films

The hydrodynamics of a flagellated microswimmer moving in thin films is discussed. The fully re- solved hydrodynamics is exploited by solving the Stokes equations for the actual geometry of the swimmer. Two different interfaces are used to confine the swimmer: a bottom solid wall and a top air-liquid inter- face, as appropriate for a thin film. The swimmer follows curved clockwise trajectories that can converge towards an asymptotically stable circular path or can result in a collision with one of the two interfaces. A bias towards the air-liquid interface emerges. Slight changes in the swimmer geometry and film thickness strongly affect the resulting dynamics suggesting that a very reach phenomenology occurs in the presence of confinement. Under specific conditions, the swimmer follows a “crown-like” path. Implications for the motion of bacteria close to an air bubble moving in a microchannel are discussed.