Confinement-induced intermittent motion of a camphor-infused paper disk.

Intermittent locomotion represents a significant area of research. This type of motion can be exhibited by individual species or groups of species, contingent upon their morphology, environmental factors, and physiological requirements. In some instances, this phenomenon contributes to the enhancement of group dynamics within a system. Intermittent motion is not limited to living systems but can also be observed in inanimate active systems. Previous research has extensively documented that camphor-based systems can generate intermittent motion characterized by irregular movements interspersed with periods of stasis. This particular type of motion has been observed in both single-camphor disk and multiple-disk systems. However, the underlying mechanisms responsible for the intermittent motion remain elusive. Here we address this question using the combination of experimental and theoretical modeling. We visualize the dissolved, local concentration of camphor released by the disk in the liquid. The concentration field shows interesting dynamic patterns as it is advected by the ambient liquid within a confinement. Intermittent motion results from formation and opening of dynamic traps that set up the evolving camphor cloud. Moreover, our findings indicate that the size of the confinement and the rate of camphor release are the key factors governing this behavior. To validate our findings, we present a mathematical model that captures the dynamics of the surrounding camphor cloud. This model successfully reproduces the ability of the disk to switch between two distinct states: the "burst" and "pause." The feedback mechanism between the surrounding camphor cloud and the disk plays a crucial role in governing these transitions.