Transient behavior of a Marangoni swimmer*

Camphor disk swimmers, one of many self-propelling active systems at the air-water interface, have been studied extensively, but some aspects of the system are yet to be explored. Although the flow field around a symmetric camphor disk swimmer has recently been studied using simulations, the structure of the flow field below such a swimmer has not been visualized experimentally. We have performed Particle Image Velocimetry (PIV) experiments on camphor disk swimmers (punched out of agarose gel sheets) self-propelling in a linear channel to visualize the flow field in the vertical plane passing through the swimmer and parallel to its swimming direction. The flow field shows a vortex structure just below the swimmer and a diverging flow behind the swimmer close to the interface. Comparing the flow fields of such a swimmer moving at constant speed with that of a swimmer changing its direction of motion shows a difference in the vortex structure of the flow field. We also study the effect of interfacial passive particles on the motion of these camphor disk swimmers to gain insight into how the swimmers behave in a complex environment.