A theoretical and experimental study on the unidirectional motion of a camphor disk

The self-sustaining motion of a camphor disk in an annular water channel was investigated. Unidirectional motion along the water channel is maintained after a local perturbation is applied to the system. Introduction of a partition into the channel changes the unidirectional motion into back-and-forth motion. To clarify the nature of the driving force that moves the settling camphor disk, the dependence of the velocity of the disk on the viscosity of the aqueous phase was measured. The experimental results are discussed in relation to the distribution of the camphor layer around the disk as the driving force. The nature of the self-motion is qualitatively reproduced by numerical computations using a mathematical model that incorporates the distribution of the camphor layer around the disk and the viscosity of the aqueous phase. Furthermore, the existence and stability of the unidirectional motion of the camphor disk depending on the viscosity of the aqueous phase are analyzed numerically. (C) 2004 Elsevier B.V. All rights reserved.