(572d) A Self-Propelling Marangoni Swimmer in a Dense Granular Mono-Layer

There are many self-propelling active systems including camphor disk swimmers. These systems have been extensively investigated, and some aspects of the system in a complex environment have yet to be explored in detail. Especially, it is not well understood how the active camphor swimmer interacts with passive particles at the air-water interface. We have performed a series of experiments on camphor disk swimmers (punched out of agarose gel sheets) self-propelling in an annular channel to characterize the interaction with passive particles (glass microspheres). Our experiments have shown that in an annular channel, the steady swimming velocity of the camphor disk decreases with increasing particle packing fraction on the interface. Moreover, there is a critical particle packing fraction where the motion of a camphor swimmer is stopped and reversed. We propose an increase in the surface viscous drag force on the swimmer and a decrease in the surface diffusion coefficient of camphor molecules in the presence of passive particles on the interface. These effects are modeled using a 1D reaction-diffusion equation for camphor and a force balance equation for the swimmer on the air-water interface.