Bifurcation of Rotational Motion of Elliptical Camphor Coated Disk

Michiko Shimokawa, Associate Professor at Dep. Physics Nara Women's University, Nara, Japan

A camphor boat is one of the famous self-propelled particles, which moves spontaneously on the water due to the difference in surface tension around the boat. The collective motions of the camphor boats resemble traffic jams and the quorum sensing in living things, and the camphor boat has been studied as an example of an active matter in non-biological systems.  Furthermore, the camphor boat has been interesting topics as bifurcation phenomena, where the behavior changes drastically at a certain value of the parameter.

When an elliptical camphor disk, with the center of mass fixed at the axis of rotation, is placed on the surface of water, it rotates
spontaneously.  We found the appearance of the bifurcation from the stable state to the rotational state in the control of the water depth. The bifurcation type, which is subcritical bifurcation or supercritical bifurcation, depended on the aspect ratio of the elliptical camphor disk.  We discussed the important factor to determine the bifurcation type through the results of our experimental results and our phenomenological model.